ORTHOPEDICS HYPERGUIDE MCQ 800-850

800. (2717) Q2-3212:

Which of the following statements concerning type II collagen in articular cartilage is false:

1) Type II collagen comprises 90% to 95% of the articular cartilage.

3) Type IX collagen regulates the type II fiber diameter.

2) The fibers are arranged parallel to the surface in the superficial or tangential zone.

5) The fibers are oriented in a perpendicular fashion in the deep or basal zone.

4) Normally, the collagen turnover is very slow.

The three types of collagen in articular cartilage are:

1. Type II

a. 90% to 95% of the total collagen

b. Highly cross-linked and interconnected

2. Type IX

a. Forms cross-links with type II

3. Type XI

a. Regulates the type II fibril diameter

In articular cartilage organization:

Cartilage layer Superficial or tangential Intermediate or transitional

Deep or basal

Collagen fiber arrangement

Parallel to the surface Oblique to the surface Perpendicular to the surface

In normal states, the collagen turnover is slow. In contrast, collagen and proteoglycan turnover can be rapid in disease states

(such as septic arthritis).

Correct Answer: Type IX collagen regulates the type II fiber diameter.

801. (2718) Q2-3213:

Which of the following articular cartilage collagens forms cross-links with type II collagen:

1) Type I

3) Type V

2) Type III

5) Type XI

4) Type IX

The three types of collagen in articular cartilage are:

1. Type II

a. 90% to 95% of the total collagen

b. Highly cross-linked and interconnected

2. Type IX

a. Forms cross-links with type II

3. Type XI

a. Regulates the type II fibril diameter

Correct Answer: Type IX

802. (2719) Q2-3214:

Which of the following factors has a chondroprotective (anabolic) function:

1) Transforming growth factor beta

3) Interleukin-1

2) Matrix metalloproteinases

5) C yclooxygenase (C OX-2)

4) Tumor necrosis factor alpha

I. C artilage Metabolism and Regulation

A. Nutrition through diffusion (low oxygen tension, 1% to 2%) B. Energy through glycolysis

C . Transforming growth factor beta (TGF-B)

1. C hondroprotective effect

2. Smad3 which is transcription factor activated by TGF-B also is chondroprotective

D. Insulin-like growth factor increases collagen and proteoglycan synthesis

E. Bone morphogenetic protein (BMP)-2 and BMP-7 increase proteoglycan synthesis and maintain chondrocyte phenotype

F. Interleukin-1

1. Inhibits proteoglycan synthesis

2. Stimulates metalloproteinase activity (catabolic enzymes) G. Tumor necrosis factor alpha

1. Inhibits collagen synthesis

2. Stimulates metalloproteinase activity (catabolic enzymes) H. Other catabolic enzymes

1. C yclooxygenase (C OX-2)

2. Nitric oxide synthetase

Chondroprotective (anabolic)

TGF-B Smad3

Insulin-like growth factor

BMP-2

BMP-7

Chondro-ablative (catabolic)

Interleukin-1

Tumor necrosis factor alpha

C OX-2

Nitric oxide synthetase

Correct Answer: Transforming growth factor beta

803. (2720) Q2-3215:

Which of the following has a catabolic effect on articular cartilage:

1) Bone morphogenetic protein (BMP)-2

3) Transforming growth factor beta

2) BMP-7

5) Smad3

4) Tumor necrosis factor alpha

I. C artilage Metabolism and Regulation

A. Nutrition through diffusion (low oxygen tension, 1% to 2%) B. Energy through glycolysis

C . Transforming growth factor beta (TGF-B)

1. C hondroprotective effect

2. Smad3 which is transcription factor activated by TGF-B also is chondroprotective

D. Insulin-like growth factor increases collagen and proteoglycan synthesis

E. Bone morphogenetic protein (BMP)-2 and BMP-7 increase proteoglycan synthesis and maintain chondrocyte phenotype

F. Interleukin-1

1. Inhibits proteoglycan synthesis

2. Stimulates metalloproteinase activity (catabolic enzymes) G. Tumor necrosis factor alpha

1. Inhibits collagen synthesis

2. Stimulates metalloproteinase activity (catabolic enzymes) H. Other catabolic enzymes

1. C yclooxygenase (C OX-2)

2. Nitric oxide synthetase

Chondroprotective (anabolic)

TGF-B Smad3

Insulin-like growth factor

BMP-2

BMP-7

Chondro-ablative (catabolic)

Interleukin-1

Tumor necrosis factor alpha

C OX-2

Nitric oxide synthetase

Metalloproteinase

Correct Answer: Tumor necrosis factor alpha

804. (2721) Q2-3216:

Which of the following has a catabolic effect on articular cartilage:

1) Bone morphogenetic protein (BMP)-2

3) Matrix metalloproteinases

2) BMP-7

5) Insulin-like growth factor 1

4) Transforming growth factor beta

I. C artilage Metabolism and Regulation

A. Nutrition through diffusion (low oxygen tension, 1% to 2%) B. Energy through glycolysis

C . Transforming growth factor beta (TGF-B)

1. C hondroprotective effect

2. Smad3 which is transcription factor activated by TGF-B also is chondroprotective

D. Insulin-like growth factor increases collagen and proteoglycan synthesis

E. Bone morphogenetic protein (BMP)-2 and BMP-7 increase proteoglycan synthesis and maintain chondrocyte phenotype

F. Interleukin-1

1. Inhibits proteoglycan synthesis

2. Stimulates metalloproteinase activity (catabolic enzymes) G. Tumor necrosis factor alpha

1. Inhibits collagen synthesis

2. Stimulates metalloproteinase activity (catabolic enzymes) H. Other catabolic enzymes

1. C yclooxygenase (C OX-2)

2. Nitric oxide synthetase

Chondroprotective (anabolic)

TGF-B Smad3

Insulin-like growth factor

BMP-2

BMP-7

Chondro-ablative (catabolic)

Interleukin-1

Tumor necrosis factor alpha

C OX-2

Nitric oxide synthetase

Metalloproteinase

Correct Answer: Matrix metalloproteinases

805. (2722) Q2-3217:

Which of the following has a catabolic effect on articular cartilage:

1) Bone morphogenetic protein (BMP)-2

3) Smad3

2) BMP-7

5) C yclooxygenase (C OX-2)

4) Insulin-like growth factor 1

I. C artilage Metabolism and Regulation

A. Nutrition through diffusion (low oxygen tension, 1% to 2%) B. Energy through glycolysis

C . Transforming growth factor beta (TGF-B)

1. C hondroprotective effect

2. Smad3 which is transcription factor activated by TGF-B also is chondroprotective

D. Insulin-like growth factor increases collagen and proteoglycan synthesis

E. Bone morphogenetic protein (BMP)-2 and BMP-7 increase proteoglycan synthesis and maintain chondrocyte phenotype

F. Interleukin-1

1. Inhibits proteoglycan synthesis

2. Stimulates metalloproteinase activity (catabolic enzymes) G. Tumor necrosis factor alpha

1. Inhibits collagen synthesis

2. Stimulates metalloproteinase activity (catabolic enzymes) H. Other catabolic enzymes

1. C yclooxygenase (C OX-2)

2. Nitric oxide synthetase

Chondroprotective (anabolic)

TGF-B Smad3

Insulin-like growth factor

BMP-2

BMP-7

Chondro-ablative (catabolic)

Interleukin-1

Tumor necrosis factor alpha

C OX-2

Nitric oxide synthetase

Metalloproteinase

Correct Answer: C yclooxygenase (C OX-2)

806. (2723) Q2-3218:

Which of the following muscle groups comprises the mobile wad of the forearm:

1) Brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevisq

3) Brachioradialis, extensor carpi radialis brevis, extensor pollicis brevis

2) Brachioradialis, extensor pollicis brevis, extensor digitorum communis

5) Extensor carpi ulnaris, extensor pollicis brevis, extensor digitorum communis

4) Brachioradialis, extensor carpi radialis brevis, extensor digitorum communis

The forearm contains the anterior, dorsal, and mobile wad. The following muscles are located in each compartment: Mobile wad

Brachioradialis

Extensor carpi radialis brevis

Extensor carpi radialis longus

Volar compartment

Flexor carpi ulnaris

Flexor digitorum profundus Flexor digitorum superficialis Palmaris longus

Flexor carpi radialis

Flexor pollicis longus

Correct Answer: Brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevisq

807. (2724) Q2-3219:

Which of the following muscles must be detached from the tibia when decompressing the deep posterior compartment of the leg:

1) Posterior tibialis

3) Medial gastrocnemius

2) Flexor hallucis longus

5) Flexor digitorum longus

4) Soleus

Of the four compartments, the deep posterior compartment is the most difficult to release. The surgeon must release the soleus muscle from the tibia to decompress the deep posterior compartment.

The tibialis posterior muscle often has its own fascial sheath in the deep posterior compartment. When a surgeon releases the deep posterior compartment, this fascial sheath (if present) should be released.

Correct Answer: Soleus

808. (2725) Q2-3220:

Which of the following leg muscles often has its own fascial envelope (separate compartment):

1) Anterior tibialis muscle

3) Peroneus longus muscle

2) Posterior tibialis muscle

5) Flexor hallucis longus muscle

4) Flexor digitorum longus muscle

Of the four compartments, the deep posterior compartment is the most difficult to release. The surgeon must release the soleus muscle from the tibia to decompress the deep posterior compartment.

The tibialis posterior muscle often has its own fascial sheath in the deep posterior compartment. When a surgeon releases the deep posterior compartment, this fascial sheath (if present) should be released.

Correct Answer: Posterior tibialis muscle

809. (2726) Q2-3221:

In patients with a tibia fracture, which of the following compartments are most prone to develop a compartment syndrome:

1) Anterior and lateral

3) Lateral and superficial posterior

2) Anterior and deep posterior

5) Superficial and deep posterior

4) Lateral and deep posterior

In a study by Heckman and colleagues, the level of the fracture site is the region with the highest tissue pressure. This was found to be true in all four components. The highest pressures are located in the anterior and deep posterior components.Correct Answer: Anterior and deep posterior

810. (2727) Q2-3222:

The approximate incidence of compartment syndrome following a tibia fracture is:

1) 1% to 2%

3) 10% to 20%

2) 5% to 10%

5) 30% to 40%

4) 20% to 30%

C ompartment syndromes occur in approximately 5% to 10% of tibia fractures. Patients with tibia fractures have the highest risk of all fracture patients.

Adult fracture patients at risk for compartment syndrome include (in descending order): Tibia shaft fractures

Femoral shaft fractures

Both bone forearm fractures

Distal radius fractures

C hildren with fractures who are at risk include (in descending order): Tibial shaft fractures

Supracondylar humerus fractures

Both bone forearm fractures

Correct Answer: 5% to 10%

811. (2728) Q2-3223:

In patients with a closed tibia fracture and suspected compartment syndrome, the region of the leg that will most likely have the highest tissue pressure measurement is:

1) The middle of the leg

3) At the level of the fracture

2) 5 cm proximal to the fracture site

5) The proximal one-third of the leg

4) 5 cm distal to the fracture site

In a study by Heckman and colleagues, the level of the fracture site is the region with the highest tissue pressure. This was found to be true in all four components. The highest pressures are located in the anterior and deep posterior components.

Correct Answer: At the level of the fracture

812. (2729) Q2-3224:

Which of the following may be beneficial in decreasing the deleterious effects of total muscle ischemia in a patient who has a compartment syndrome:

1) Systemic steroids

3) Elevation of the extremity above the heart

2) Hypothermia

5) Anticoagulant therapy

4) Antihypertensive therapy

Aside from performing a fasciotomy, little can be done for patients with a compartment syndrome. Hypothermia, systemic corticosteroids, and anticoagulation therapy may increase muscle tolerance to ischemia.

Steroids and anticoagulation are not reasonable options because there is an impaired blood supply to the muscle (ie, these agents cannot enter the muscle). Hypothermia can be used to gain some time if immediate fasciotomy cannot be performed.

Correct Answer: Hypothermia

813. (2730) Q2-3225:

Which of the following is the most sensitive finding in patients who are at risk for compartment syndrome before total muscle and nerve ischemia occurs:

1) Paresthesia

3) Pain on passive stretch of muscle

2) Loss of peripheral pulses

5) Loss of motor function

4) Delayed capillary refill

C ompartment syndromes are difficult to diagnose. It is important to diagnosis compartment syndrome before irreversible muscle and nerve damage occurs.

Pain out of proportion to the injury and pain with passive stretch are the most important subjective and objective findings before a compartment syndrome has fully developed. Pain will subside after a prolonged period of ischemia. The muscle and nerves in the compartment are no longer viable, and the pain will diminish.

Correct Answer: Pain on passive stretch of muscle

814. (2731) Q2-3226:

Which of the following is the normal resting pressure in skeletal muscle:

1) 0 mm Hg to 8 mm Hg

3) 18 mm Hg to 24 mm Hg

2) 10 mm Hg to 16 mm Hg

5) 30 mm Hg to 36 mm Hg

4) 24 mm Hg to 30 mm Hg

Normal resting muscle tissue pressure is between 0 mm Hg and 8 mm Hg. Remember, if one squeezes the muscle or pushes on it, then the compartment pressure increases.

Normal tissues have adequate tissue perfusion with increases in compartment pressure to within 10 mm Hg of the diastolic pressure. In damaged tissue (eg, tibia fracture), perfusion can be impaired when the diastolic pressure reaches within 20 mm Hg of the diastolic pressure.

One should remember that hypotensive patients with extremity injuries are prone to compartment syndromes. Correct Answer: 0 mm Hg to 8 mm Hg

815. (2732) Q2-3227:

In injured tissues, ischemia begins when the tissue pressure within the compartment comes within mm Hg of the diastolic pressure.

1) 10

3) 30

2) 20

5) 50

4) 40

Normal tissues have adequate tissue perfusion with increases in compartment pressure to within 10 mm Hg of the diastolic pressure. In damaged tissue (eg, tibia fracture), perfusion can be impaired when the diastolic pressure reaches within 20 mm Hg of the diastolic pressure.

One should remember that hypotensive patients with extremity injuries are prone to compartment syndromes. Correct Answer: 20

816. (2733) Q2-3229:

C omplete ischemia of a peripheral nerve results in irreversible damage after hours.

1) 1 to 2 hours

3) 4 to 6 hours

2) 2 to 4 hours

5) 8 to 10 hours

4) 6 to 8 hours

Loss of nerve electrical conduction begins after 2 hours of complete ischemia. Peripheral nerves can tolerate up to 4 hours of complete ischemia. A neurapraxic (loss of conduction capability) injury usually recovers. After 8 hours of complete ischemia, nerves cannot recover.

Patients will lose the sense of pain in a compartment with total ischemia after 2 to 8 hours because there is no conduction to the nerve. One can expect little recovery once this painless state has occurred.

Correct Answer: 8 to 10 hours

817. (2734) Q2-3230:

C omplete muscle ischemia that leads to irreversible muscle damage occurs after which of the following time periods:

1) 1 to 2 hours

3) 4 to 6 hours

2) 2 to 4 hours

5) 8 to 10 hours

4) 6 to 8 hours

Skeletal muscle tolerates periods of complete muscle ischemia for 3 to 4 hours without irreversible damage. Variable recovery occurs with ischemia for 6 to 8 hours. When the period of ischemia is more than 8 hours, there is irreversible muscle damage. After 8 hours, the muscle cells degenerate and, grossly, the muscle contracts as the muscle cells are replaced with scar tissue and contracture may result.

Remember to let a tourniquet down after 2 hours of ischemia. One does not want to enter the tolerance period of 3 to 4 hours. Correct Answer: 8 to 10 hours

818. (2735) Q2-3231:

Skeletal muscle may remain viable (electrically responsive) following a period of total ischemia. Which of the following is the correct time interval for the tolerance to total muscle ischemia (complete recovery can be expected):

1) 3 to 4 hours

3) 6 to 8 hours

2) 4 to 6 hours

5) 10 to 12 hours

4) 8 to 10 hours

Skeletal muscle tolerates periods of complete muscle ischemia for 3 to 4 hours without irreversible damage. Variable recovery occurs with ischemia for 6 to 8 hours. When the period of ischemia is more than 8 hours, there is irreversible muscle damage. After 8 hours, the muscle cells degenerate and, grossly, the muscle contracts as the muscle cells are replaced with scar tissue and contracture may result.

Remember to let a tourniquet down after 2 hours of ischemia. One does not want to enter the tolerance period of 3 to 4 hours. Correct Answer: 3 to 4 hours

819. (2779) Q2-3277:

Which of the following statements concerning locking plates is true:

1) The pullout strength of a locked unicortical screw is only 30% of a standard bicortical screw.

3) Locked bicortical screws have greater toggle than standard bicortical screws.

2) Toggle between the screws and plate is greater than standard plating.

5) Locked plating is biomechanically similar to external fixation with a lower moment arm.

4) Friction between the plate and cortical bone is greater in locked plating compared to standard plating.

Locking plates have become a popular, effective method of stabilizing metaphyseal/epiphyseal fractures with comminution and short articular fragments.

Important biomechanical features of locking plates include1 :

Locked screws can function as individual blade plates in the distal fragment.

Locking plates can effectively serve as bridge plates, providing excellent fixation in short distal articular fragments. C ompression of the plate against the bone is less than that of conventional plating, resulting in less devascularization of the underlying cortex.

There is no toggling between the locked screws and the plate.

The pullout strength of a locked unicortical screw is approximately 60% of a standard bicortical screw. Locking plates are similar biomechanically to an external fixator.

Moment arms are less because the plate is closer to the bone's neutral axis than the connecting bar of the external fixator.

Correct Answer: Locked plating is biomechanically similar to external fixation with a lower moment arm.

820. (2780) Q2-3278:

Which of the following statements concerning locking plates is true:

1) The pullout strength of a locked unicortical screw is only 60% of a standard bicortical screw.

3) Locked bicortical screws have greater toggle than standard bicortical screws.

2) Toggle between the screws and plate is greater than standard plating.

5) Locked plating is not biomechanically similar to external fixation with a lower moment arm.

4) Friction between the plate and cortical bone is greater in locked plating compared to standard plating.

Locking plates have become a popular and effective method of stabilizing metaphyseal/epiphyseal fractures with comminution and short articular fragments.

Important biomechanical features of locking plates include:

locked screws can function as individual blade plates in the distal fragment locking plates can effective serve as bridge plates

excellent fixation in short distal articular fragments

compression of the plate against the bone is less than that of conventional plating less devascularization of the underlying cortex

there is no toggling between the locked screws and the plate

pullout strength of a locked unicortical screw is approximately 60% a standard bicortical screw

locking plates are similar biomechanically to an external fixator moment arms are less because the plate is closer to the bone's neutral axis than the connecting bar of the external fixator

Correct Answer: The pullout strength of a locked unicortical screw is only 60% of a standard bicortical screw.

821. (2781) Q2-3279:

Which of the following describes the inheritance pattern of hemophilia A:

1) Autosomal dominant inheritance

3) Sex-linked dominant

2) Autosomal recessive inheritance

5) Sporadic

4) Sex-linked recessive

Hemophilia A is transmitted by a sex-linked recessive inheritance pattern. Important points to remember:

Hemophilia A (classic hemophilia) Factor VIII deficiency

Sex-linked recessive trait

Incidence - 1/5000 live male births

25% of cases are sporadic (no family history) Hemophilia B (C hristmas disease)

Factor IX deficiency

Sex-linked recessive trait

Incidence - 1/30,000 live male births

Correct Answer: Sex-linked recessive

822. (2782) Q2-3280:

Which of the following is the most important pathophysiology factor in hemophilic arthropathy:

1) Viral joint infection

3) Hemosiderin depositionq

2) Bacterial joint infection

5) Neuropathic damage

4) Subchondral bone microfractures

Hemosiderin deposition leads to synovial hypertrophy, bone erosions, recurrent bleeding, and eventual destruction of the articular surfaces and arthrofibrosis.

Synovial A cells (surface layer phagocytic cells) ingest hemosiderin

Mixed inflammatory cell population

Lymphocytes Plasma cells Histiocytes

Leads to bone erosion from the thickened synovium

Correct Answer: Hemosiderin depositionq

823. (2965) Q2-3471:

The âbystander effectâ in cancer gene therapy is:

1) Resistance to gene therapy by neighbor tumor cells after irradiation.

3) The death of neighbor untargeted tumor cells during cell-targeted suicide.

2) The secretion of tumor suppressor cytokines by neighbor cells.

5) None of the above.

4) Anaphylaxis-like side effects seen during tumor gene therapy.

The âbystander effectâ is the death of neighbor untargeted tumor cells during cell-targeted suicide, whereby HSV thymine kinase gene targeted cells commit suicide by absorbing gancyclovir, a prodrug that is turned intracellularly into a toxic metabolite by the targeting gene through phosphorylation.Correct Answer: The death of neighbor untargeted tumor cells during cell-targeted suicide.

824. (2991) Q2-3497:

Which of the following is associated with cleidocranial dysplasia:

1) Type X collagen

3) C artilage oligomeric protein

2) C arbonic anhydrase type II, proton pump

5) C ore binding factor alpha 1 (C bfa1)

4) Fibrillin

The defect in cleidocranial dysplasia involves C bfa1.

C bfa1 is a transcription factor (coded by the C bfa1 gene) that is necessary and sufficient for differentiation of cells into osteoblasts and facilitates chondrocyte differentiation during enchondral bone formation.

The other responses refer to:

Metaphyseal chondrodysplasia (Schmid type): Type X collagen Osteopetrosis: C arbonic anhydrase type II, proton pump Metaphyseal epiphyseal dysplasia: C artilage oligomeric protein Marfan's syndrome: Fibrillin

Correct Answer: C ore binding factor alpha 1 (C bfa1)

825. (2992) Q2-3498:

Which of the following is associated with achondroplasia:

1) Type X collagen

3) Fibrillin

2) Sulfate transporter gene

5) Type I collagen (C ol 1A1, 1A2)

4) Fibroblast growth factor 3 (FGF-3) (receptor)

Achondroplasia is caused by a defect in FGF-3 receptor, resulting in an inhibition of chondrocyte proliferation in the proliferative zone of the physis. One possible theory is that this mutation results in a receptor that is active even without binding of the fibroblast growth factor ligand, thereby causing an overactive receptor. This is a gain of function mutation (Dietz).

The other responses refer to:

Metaphyseal chondrodysplasia (Schmid type): Type X collagen

Diastrophic dysplasia: Sulfate transporter gene Osteogenesis imperfecta: Type I collagen (C ol 1A1, 1A2) Marfanâs syndrome: Fibrillin

Correct Answer: Fibroblast growth factor 3 (FGF-3) (receptor)

826. (2993) Q2-3499:

Which of the following defects occurs in Albright hereditary osteodystrophy (pseudohypoparathyroidism):

1) Type X collagen

3) Beta glucosidase

2) Sulfate transporter gene

5) C arbonic anhydrase type II, proton pump

4) Galpha S (GNAS1)

Pseudohypoparathyroidism (PHP) (Albright Hereditary Osteodystrophy [AHO]) - end organ insensitivity; in AHO, germline mutation that leads to loss of function of Galpha S (GNAS1); causes end-organ resistance to PTH (Zaleske).

1. PHP - short stature, short metacarpals (4th and 5th), rounded facies a. Mental retardation, tetany

b. Sex-linked dominant

2. Laboratory features a. Hypocalcemia

b. Hyperphopshatemia c. Normal PTH

3. Other features

The other responses refer to:

Metaphyseal chondrodysplasia (Schmid type): Type X collagen

Diastrophic dysplasia: Sulfate transporter gene

Gaucher's disease: Beta glucosidase

Osteopetrosis: C arbonic anhydrase type II, proton pump

Correct Answer: Galpha S (GNAS1)

827. (2994) Q2-3500:

Which of the following is associated with Marfan's syndrome:

1) Sulfate transporter gene

3) C arbonic anhydrase type II, proton pump

2) Fibroblast growth factor 3 (FGF-3) (receptor)

5) Fibrillin

4) C ore binding factor alpha 1 (C bfa1)

The defective gene (located on chromosome 15) in Marfan's syndrome encodes for fibrillin. Fibrillin is a structural component of elastin and contains microfibrils (Dietz).

Features of Marfan's syndrome include: Long, thin limbs (dolichostenomelia)

Pectus excavatum, carinatum

Scoliosis

High and narrow palate

Ectopia lentis

Dilation of the ascending aorta

Dural ectasia

The other responses refer to:

Achondroplasia: FGF-3 receptor

Diastrophic dysplasia: Sulfate transporter gene

C leidocranial dysplasia: C bfa1

Osteopetrosis: C arbonic anhydrase type II, proton pump

Correct Answer: Fibrillin

828. (3003) Q2-3509:

Which of the following proteins binds to osteoclast precursor cells and positively effects their final differentiation into osteoclasts:

1) Receptor activator of nuclear factor-kB (RANK)

3) Bone morphogenetic protein-7

2) Osteoprotegerin

5) Parathyroid hormone related protein (PTHrP)

4) C ore binding factor alpha 1 (C bfa1)

Four proteins that regulate osteoclast activation have been discovered:

1. RANK binds to a receptor on osteoclast precursor cells and positively effects their final differentiation into osteoclasts.

2. Osteoprotegerin is a soluble decoy receptor that resembles RANK and inhibits osteoclasts.

3. Tumor necrosis factor-related activation induced cytokine (TRANC E)

4. Osteoclast differentiation factor

Note:

C bfa1 is a transcription factor (coded by the C bfa1 gene) that is necessary and sufficient for differentiation of cells into osteoblasts and facilitates chondrocyte differentiation during enchondral bone formation.

Correct Answer: Receptor activator of nuclear factor-kB (RANK)

829. (3004) Q2-3510:

Which of the following proteins negatively affects osteoclast precursor cells:

1) Receptor activator of nuclear factor-kB (RANK)

3) Bone morphogenetic protein-7

2) Osteoprotegerin

5) Parathyroid hormone related protein (PTHrP)

4) C ore binding factor alpha 1 (C bfa1)

Four proteins that regulate osteoclast activation have been discovered:

1. RANK binds to a receptor on osteoclast precursor cells and positively effects their final differentiation into osteoclasts.

2. Osteoprotegerin is a soluble decoy receptor that resembles RANK and inhibits osteoclasts.

3. Tumor necrosis factor-related activation induced cytokine (TRANC E)

4. Osteoclast differentiation factor

Note:

C bfa1 is a transcription factor (coded by the C bfa1 gene) that is necessary and sufficient for differentiation of cells into osteoblasts and facilitates chondrocyte differentiation during enchondral bone formation.

Correct Answer: Osteoprotegerin

830. (3005) Q2-3511:

Which of the following proteins or genes is necessary for bone formation and induces osteocalcin:

1) Sox-9 gene

3) Tumor necrosis factor-related activation induced cytokine

2) Receptor activator of nuclear factor-kB protein

5) C ore binding factor alpha 1 (Cbfa1) gene

4) Osteoprotegerin

C ore binding factor alpha 1 (C bfa1) and its gene (Cbfa1) have been described as anabolic regulators of bone. C bfa1 is a transcription factor and is responsible for the differentiation of precursor cells into osteoblasts. It also enhances differentiation of chondrocytes during enchondral bone formation. When there is deficiency of C bfa1, there can be abnormal bone development as in cleidocranial dysplasia.

Correct Answer: C ore binding factor alpha 1 (Cbfa1) gene

831. (3006) Q2-3512:

The human genome is comprised of approximately how many genes:

1) 1,000

3) 10,000

2) 5,000

5) 100,000

4) 30,000

The human genome is composed of 30,000 unique genes. Each gene is composed of a promotor or regulator region, and a transcriptional or coding region. Regulatory proteins or transcription factors bind to the promoter region of the gene to signal the beginning of transcription of the DNA into RNA or repress the expression of the gene. The coding region contains both introns and exons. Exon sequences of the gene directly code for the proteins, and the introns are spacers. The intron sequences are enzymatically removed from the newly transcribed messenger RNA by a splicing mechanism.

Correct Answer: 30,000

832. (3007) Q2-3513:

Which of the following portions of a gene directly codes for the messenger RNA for eventual translation into proteins on the ribosome:

1) Promoter region

3) Exon

2) Intron

5) Activator or repressor binding site

4) C oding region

The human genome is composed of 30,000 unique genes. Each gene is composed of a promotor or regulator region, and a transcriptional or coding region. Regulatory proteins or transcription factors bind to the promoter region of the gene to signal the beginning of transcription of the DNA into RNA or repress the expression of the gene. The coding region contains both introns and exons. Exon sequences of the gene directly code for the proteins, and the introns are spacers. The intron sequences are enzymatically removed from the newly transcribed messenger RNA by a splicing mechanism.

Correct Answer: Exon

833. (3008) Q2-3514:

Which of the following describes the inheritance pattern of achondroplasia:

1) X-linked recessive

3) Autosomal dominant

2) Sporadic

5) X-linked dominant

4) Autosomal recessive

Structural defects are usually transmitted by an autosomal-dominant pattern. In contrast, with metabolic or enzyme deficiencies, the condition is usually transmitted in an autosomal-recessive pattern.

Remember the major autosomal-dominant conditions:

Achondroplasia Spondyloepiphyseal dysplasia Multiple epiphyseal dysplasia Marfan's syndrome

Ehlers-Danlos syndrome Osteogenesis imperfecta (I, IV) Multiple hereditary exostosis Polydactyly

Correct Answer: Autosomal dominant

834. (3009) Q2-3515:

Which of the following describes the inheritance pattern of Marfanâs syndrome:

1) Autosomal recessive

3) X-linked recessive

2) Autosomal dominant

5) Sporadic

4) X-linked dominant

Structural defects are usually transmitted by an autosomal-dominant pattern. In contrast, with metabolic or enzyme deficiencies, the condition is usually transmitted in an autosomal-recessive pattern.

Remember the major autosomal-dominant conditions: Achondroplasia

Spondyloepiphyseal dysplasia

Multiple epiphyseal dysplasia

Marfan's syndrome Ehlers-Danlos syndrome Osteogenesis imperfecta (I, IV) Multiple hereditary exostosis Polydactyly

Correct Answer: Autosomal dominant

835. (3010) Q2-3516:

Which of the following describes the inheritance pattern of Ehlers-Danlos syndrome:

1) Autosomal recessive

3) X-linked recessive

2) Autosomal dominant

5) Sporadic

4) X-linked dominant

Structural defects are usually transmitted by an autosomal-dominant pattern. In contrast, with metabolic or enzyme deficiencies, the condition is usually transmitted in an autosomal-recessive pattern.

Remember the major autosomal-dominant conditions: Achondroplasia

Spondyloepiphyseal dysplasia

Multiple epiphyseal dysplasia

Marfan's syndrome

Ehlers-Danlos syndrome Osteogenesis imperfecta (I, IV) Multiple hereditary exostosis Polydactyly

Correct Answer: Autosomal dominant

836. (3011) Q2-3517:

Which of the following describes the inheritance pattern of multiple hereditary exostoses:

1) Autosomal dominant

3) X-linked dominant

2) Autosomal recessive

5) Sporadic

4) X-linked recessive

Structural defects are usually transmitted by an autosomal-dominant pattern. In contrast, with metabolic or enzyme deficiencies, the condition is usually transmitted in an autosomal-recessive pattern.

Remember the major autosomal-dominant conditions: Achondroplasia

Spondyloepiphyseal dysplasia

Multiple epiphyseal dysplasia

Marfan's syndrome Ehlers-Danlos syndrome Osteogenesis imperfecta (I, IV) Multiple hereditary exostosis Polydactyly

Correct Answer: Autosomal dominant

837. (3012) Q2-3518:

Which of the following describes the inheritance pattern of polydactyly:

1) Autosomal recessive

3) X-linked recessive

2) Autosomal dominant

5) Sporadic

4) X-linked dominant

Structural defects are usually transmitted by an autosomal-dominant pattern. In contrast, with metabolic or enzyme deficiencies, the condition is usually transmitted in an autosomal-recessive pattern.

Remember the major autosomal-dominant conditions: Achondroplasia

Spondyloepiphyseal dysplasia

Multiple epiphyseal dysplasia

Marfan's syndrome Ehlers-Danlos syndrome Osteogenesis imperfecta (I, IV) Multiple hereditary exostosis Polydactyly

Correct Answer: Autosomal dominant

838. (3013) Q2-3519:

Which of the following describes the inheritance pattern of hypophosphatasia:

1) Austosomal dominant

3) X-linked dominant

2) Austosomal recessive

5) Sporadic

4) X-linked recessive

Structural defects are usually transmitted by an autosomal-dominant pattern. In contrast, with metabolic or enzyme deficiencies, the condition is usually transmitted in an autosomal-recessive pattern.

Remember the major autosomal-recessive conditions: Sickle cell disease

Osteogenesis imperfecta (Types II, III)

Hypophosphatasia Homocystinuria Gaucher's disease

Correct Answer: Austosomal recessive

839. (3014) Q2-3520:

Which of the following describes the inheritance pattern of sickle cell disease:

1) Autosomal dominant

3) X-linked dominant

2) Autosomal recessive

5) Sporadic

4) X-linked recessive

Structural defects are usually transmitted by an autosomal-dominant pattern. In contrast, with metabolic or enzyme deficiencies, the condition is usually transmitted in an autosomal-recessive pattern.

Remember the major autosomal-recessive conditions:

Sickle cell disease

Osteogenesis imperfecta (Types II, III) Hypophosphatasia

Homocystinuria

Gaucher's disease

Correct Answer: Autosomal recessive

840. (3015) Q2-3521:

Which of the following describes the inheritance pattern of Gaucher's disease:

1) Autosomal dominant

3) X-linked dominant

2) Autosomal recessive

5) Sporadic

4) X-linked recessive

Structural defects are usually transmitted by an autosomal-dominant pattern. In contrast, with metabolic or enzyme deficiencies, the condition is usually transmitted in an autosomal-recessive pattern.

Remember the major autosomal-recessive conditions: Sickle cell disease

Osteogenesis imperfecta (Types II, III)

Hypophosphatasia Homocystinuria Gaucher's disease

Correct Answer: Autosomal recessive

841. (3016) Q2-3522:

Which of the following describes the inheritance pattern of homocystinuria:

1) Autosomal recessive

3) X-linked recessive

2) Autosomal dominant

5) Sporadic

4) X-linked dominant

Structural defects are usually transmitted by an autosomal-dominant pattern. In contrast, with metabolic or enzyme deficiencies, the condition is usually transmitted in an autosomal-recessive pattern.

Remember the major autosomal-recessive conditions: Sickle cell disease

Osteogenesis imperfecta (Types II, III)

Hypophosphatasia Homocystinuria Gaucher's disease

Correct Answer: Autosomal recessive

842. (3017) Q2-3523:

Which of the following describes the inheritance pattern for hypophosphatemic rickets:

1) Autosomal dominant

3) X-linked dominant

2) Autosomal recessive

5) Sporadic

4) X-linked recessive

C ommon inheritance patterns that should be known for examinations:

Autosomal dominant

Autosomal recessive

X-linked dominant

X-linked recessive

Achondroplasia Sickle cell Hypophosphatemic rickets Hemophilia (A, B)

SED (congenital) OI (II, III) Duchennes muscular dystrophy

MED Hypophosphatasia Hunters syndrome

Marfanâs syndrome Homocystinuria SED (tarda)

Ehlers-Danlos syndrome Gaucherâs disease Beckerâs muscular dystrophy

Abbreviations: OI (I,IV)=Osteogenesis imperfecta, SED=Spondyloepiphyseal dysplasia, MED=Multiple epiphyseal dysplasia, MHE=Multiple hereditary exostosis

Correct Answer: X-linked dominant

843. (3018) Q2-3524:

Which of the following describes the inheritance pattern for hemophilia A:

1) Autosomal dominant

3) X-linked dominant

2) Autosomal recessive

5) Sporadic

4) X-linked recessive

C ommon inheritance patterns are shown in the Table below:

Autosomal dominant

Autosomal recessive

X-linked dominant

X-linked recessive

Achondroplasia Sickle cell Hypophosphatemic rickets Hemophilia (A, B)

SED (congenital) OI (II, III) Duchennes muscular dystrophy

MED Hypophosphatasia Hunters syndrome

Marfanâs syndrome Homocystinuria SED (tarda)

Ehlers-Danlos syndrome Gaucherâs disease Beckerâs muscular dystrophy

Abbreviations: OI (I,IV)=Osteogenesis imperfecta, SED=Spondyloepiphyseal dysplasia, MED=Multiple epiphyseal dysplasia, MHE=Multiple hereditary exostosis

Correct Answer: X-linked recessive

844. (3019) Q2-3525:

Which of the following describes the inheritance pattern of Duchennes muscular dystrophy:

1) Autosomal dominant

3) X-linked dominant

2) Autosomal recessive

5) Sporadic

4) X-linked recessive

C ommon inheritance patterns that should be known for examinations:

Autosomal dominant

Autosomal recessive

X-linked dominant

X-linked recessive

Achondroplasia Sickle cell Hypophosphatemic rickets Hemophilia (A, B)

SED (congenital) OI (II, III) Duchennes muscular dystrophy

MED Hypophosphatasia Hunters syndrome

Marfanâs syndrome Homocystinuria SED (tarda)

Ehlers-Danlos syndrome Gaucherâs disease Beckerâs muscular dystrophy

Abbreviations: OI (I,IV)=Osteogenesis imperfecta, SED=Spondyloepiphyseal dysplasia, MED=Multiple epiphyseal dysplasia, MHE=Multiple hereditary exostosis

Correct Answer: X-linked recessive

845. (3020) Q2-3526:

Which of the following describes the inheritance pattern of Becker's muscular dystrophy:

1) Autosomal dominant

3) X-linked dominant

2) Autosomal recessive

5) Sporadic

4) X-linked recessive

C ommon inheritance patterns that should be known for examinations:

Autosomal dominant

Autosomal recessive

X-linked dominant

X-linked recessive

Achondroplasia Sickle cell Hypophosphatemic rickets Hemophilia (A, B)

SED (congenital) OI (II, III) Duchennes muscular dystrophy

MED Hypophosphatasia Hunters syndrome

Marfanâs syndrome Homocystinuria SED (tarda)

Ehlers-Danlos syndrome Gaucherâs disease Beckerâs muscular dystrophy

Abbreviations: OI (I,IV)=Osteogenesis imperfecta, SED=Spondyloepiphyseal dysplasia, MED=Multiple epiphyseal dysplasia, MHE=Multiple hereditary exostosis

Correct Answer: X-linked recessive

846. (3021) Q2-3527:

Which of the following conditions is transmitted by an X-linked dominant inheritance pattern:

1) Hemophilia A

3) Duchennes muscular dystrophy

2) Hypophosphatemic rickets

5) Hypophosphatasia

4) Achondroplasia

There is only one condition that must be remembered for examinations that is transmitted through an X-linked dominant pattern - hypophosphatemic rickets.

Remember: the conditions which are x-linked recessive

Hemophilia A, B - X-linked recessive

Duchennes muscular dystrophy - X-linked recessive Achondroplasia - Autosomal dominant Hypophosphatasia - Autosomal recessive

Correct Answer: Hypophosphatemic rickets

847. (3022) Q2-3528:

Which of the following conditions is transmitted by an autosomal-dominant pattern:

1) Hemophilia A

3) Hypophosphatemic rickets

2) Achondroplasia

5) Hypophosphatasia

4) Duchennes muscular dystrophy

Achondroplasia has an autosomal-dominant pattern of inheritance. Structural problems are usually transmitted via autosomal- dominant pattern.

If an affected individual is married to an unaffected person, then the chance of transmission to the children is 50%. The other conditions have the following transmission pattern:

Hemophilia A, B - X-linked recessive

Duchennes muscular dystrophy - X-linked recessive Achondroplasia - Autosomal dominant Hypophosphatasia - Autosomal recessive

Correct Answer: Achondroplasia

848. (3023) Q2-3529:

A man with an autosomal-dominant condition married a woman without the condition. What is the probability that one of the offspring will be affected:

1) 0%

3) 50%

2) 25%

5) 100%

4) 75%

For autosomal dominant, if one parent is a heterozygote and the other is normal, then the risk of transmission is to 50% of the offspring. Because of the dominance of the allele, heterozygotes manifest the condition.

For autosomal recessive, parents are usually not affected because they are heterozygotes. The risk of transmission is to 25% of the offspring. The children must have both recessive alleles to be affected.

Correct Answer: 50%

849. (3024) Q2-3530:

A man with a single autosomal-recessive gene marries a woman who does not carry the recessive gene. The chance of one of the children expressing the phenotype of the recessive gene is:

1) 0%

3) 50%

2) 25%

5) 100%

4) 75%

For autosomal dominant, if one parent is a heterozygote and the other is normal, then the risk of transmission is to 50% of the offspring. Because of the dominance of the allele, heterozygotes manifest the condition.

For autosomal recessive, parents are usually not affected because they are heterozygotes. The risk of transmission is to 25% of the offspring. The children must have both recessive alleles to be affected.

Because only one parent contains the gene, none of the children will be affected, although 25% of the children will carry the recessive gene.

Correct Answer: 0%

850. (3025) Q2-3531:

A man with a single autosomal-recessive gene marries a woman who does not carry the recessive gene. The chance of one of the children carrying the recessive gene is:

1) 0%

3) 50%

2) 25%

5) 100%

4) 75%

For autosomal dominant, if one parent is a heterozygote and the other is normal, then the risk of transmission is to 50% of the offspring. Because of the dominance of the allele, heterozygotes manifest the condition.

For autosomal recessive, parents are usually not affected because they are heterozygotes. The risk of transmission is to 25% of the offspring. The children must have both recessive alleles to be affected.

Because only one parent contains the gene, none of the children will be affected, although 25% of the children will carry the recessive gene.

Correct Answer: 25%