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Integumentary and Skeletal Systems—Orthopedics, Dermatology, Rheumatology

Questions

428. A newborn African American girl is resuscitated during delivery and found to have a very small chest with deformed ribs, multiple rib and shoulder girdle fractures occurring during delivery, short limbs, and bluishgray sclerae (whites of the eyes). A diagnosis is suspected and a skin biopsy is taken before death so that the responsible protein can be examined for amino acid changes. Which of the following indicates the protein, disease, and the mutated 3-amino acid motif most likely to cause severe disease?

a. Fibrillin, Marfan syndrome, Pro-X-Y mutated to Gly-X-Y in one repeat

b. Collagen, osteogenesis imperfecta, Ala-X-Y mutated to Leu-X-Y in one repeat

c. Fibrillin, Marfan syndrome, Ala-X-Y mutated to Gly-X-Y in one repeat

d. Collagen, osteogenesis imperfecta, Gly-X-Y mutated to Ala-X-Y in one repeat

e. Collagen, osteogenesis imperfecta, Gly-X-Y mutated to Pro-X-Y in one repeat

429. A 15-year-old Caucasian adolescent presents with chest pain on exertion. He is noted to be very tall and thin, with lax joints that enable him to do tricks for his friends. His chest is very concave (pectus excavatum), and he has flat feet. His physician suspects Marfan syndrome (MIM*154700) and orders DNA testing for fibrillin, the gene that causes Marfan syndrome. The physician explains that fibrillin gene testing is not very sensitive, because it is a large gene with many variations, and each Marfan family tends to have a different type of mutation. Which of the following amino acid changes (derived from the DNA sequence) would be most likely to represent a pathogenetic mutation rather than benign variation (polymorphism)?

a. gly-ser-ala to gly-ser-ser

b. gly-ser-ala to gly-ser-arg

c. gly-ser-ala to gly-ser-gly

d. gly-ser-ala to gly-ser-tyr

e. gly-ser-ala to gly-ser-val

430. A 3-year-old Asian boy presents with multiple blisters over his extremities, first in response to scrapes or bruises, but then appearing regularly with illnesses or at contact sites for clothes, etc. The group of heritable diseases called epidermolysis bullosa (blistering skin—eg, MIM*131900) is suspected, and the diagnosis is confirmed by DNA testing with a mutation in the gene encoding type 5 keratin. The keratins are notable for their high content of which of the following?

a. Tyrosine

b. Proline

c. Cystine

d. Melanin

e. Serine

431. During synthesis of mature collagen fibers, which of the following steps occurs within the fibroblast?

a. Hydrolysis of procollagen to form collagen

b. Glycosylation of proline residues

c. Formation of a triple helix

d. Formation of covalent cross-links between molecules

e. Assembly of the collagen fiber

432. A 1-year-old Hispanic boy is removed from parental care because of his second femoral fracture, both from falls that seemed insufficient to cause a severe break. Medical evaluation reveals a head size at the 90th percentile for age compared to a height at the 25th percentile for age, bluish-gray whites of the eyes (sclerae), and increased joint laxity. Skeletal radiographs show a healed right femoral fracture, recent left femoral fracture, and thin bones with several small fractures on both arms and lower legs. He is evaluated for osteogenesis imperfecta (MIM*166200) by taking a skin biopsy and examining the electrophoretic mobility of type I collagen proteins synthesized by cultured fibroblasts. Amino acids labeled with radioactive carbon 14 are added to the culture dishes in order to label the collagen. Which of the following amino acids would not result in labeled collagen?

a. Serine

b. Glycine

c. Aspartate

d. Glutamate

e. Hydroxyproline

433. A 13-year-old Caucasian adolescent of French Canadian descent develops hemiballismus (repetitive throwing motions of the arms) after anesthesia for a routine operation. She is tall and lanky, and it is noted that she and her sister both had previous operations for dislocated lenses of the eyes. The symptoms are suspicious for the disease homocystinuria (MIM*236300). Which of the following statements is descriptive of this disease?

a. Patients may be treated with dietary supplements of vitamin B₁₂.

b. Patients may be treated with dietary supplements of vitamin C.

c. There is deficient excretion of homocysteine.

d. There is deficient excretion of cysteine.

e. There is a defect in the ability to form cystathionine from homocysteine and serine.

434. An 8-year-old African boy from a Somali refugee camp presents with a red, scaly rash that is made worse by sunlight (photosensitive) and a poorly coordinated gait (ataxia). The rash resembles that of pellagra, a disease resulting from niacin (vitamin B₃) deficiency, and suggests malnutrition. However, his parents report that two siblings have had the same rash, and are affected with a disorder called Hartnup disease (MIM*234500). In this disorder, patients have a defect in neutral amino acid absorption from the intestine and become deficient in neutral amino acids (those with uncharged side chains). The physician reads about Hartnup disease and decides the rashes are likely to be pellagra, caused by deficiency of niacin. Which of the following abnormalities in Hartnup disease would account for the niacin deficiency?

a. Deficiency of lysine

b. Deficiency of arginine

c. Deficiency of taurine

d. Deficiency of aspartic acid

e. Deficiency of glutamic acid

f. Deficiency of ornithine

g. Deficiency of tryptophan

435. A 2-day-old Caucasian boy develops jaundice (yellow skin and yellow sclerae) that is greater than average at its usual peak at 3 days and requires laboratory evaluation. Which of the following porphyrin derivatives is conjugated, reacts directly, and is a major component of bile?

a. Bilirubin diglucuronide

b. Stercobilin

c. Biliverdin

d. Urobilinogen

e. Heme

436. It has been noted that infants placed on extremely low-fat diets for a variety of reasons often develop skin problems and other symptoms. This is most often due to which of the following?

a. Lactose intolerance

b. Glycogen storage diseases

c. Antibody abnormalities

d. Deficiency of fatty acid desaturase greater than Δ⁹

e. Deficiency of chylomicron and VLDL production

437. A 15-month-old boy from Nigeria is evaluated for developmental delay. His coloring seems much lighter than that of his family background, and his physician orders a blood amino acid test that demonstrates elevated phenylalanine. A special low phenylalanine formula is begun (Lofenalac) as treatment for phenylketonuria (MIM*261600), but the parents refuse to come in for follow-up appointments. A public health evaluation reports that the child is failing to thrive despite apparent adherence to the diet by his parents. The symptoms of decreased skin pigment and later failure to thrive in this child are most likely related to which of the following?

a. Deficiency of alanine

b. Deficiency of tyrosine and melanin

c. Deficiency of tryptophan and niacin

d. Deficiency of leucine and isoleucine

e. Deficiency of phenylalanine

438. A 52-year-old Caucasian male seeks evaluation for sleeplessness because his great toes become swollen, red, and painful each night. Examination reveals small, moveable lumps (nodules) on his ears, fingers, and toes. His physician makes a diagnosis of gout and is informed that two of the man’s six siblings are affected with the disease. Which of the following enzyme defects might be responsible for hereditary gout in this family?

a. Adenylosuccinase

b. Formyltransferase

c. IMP cyclohydrolase

d. PRPP glutamyl amidotransferase

e. PRPP synthetase

439. Which of the following compounds is an analog of hypoxanthine?

a. Ara C

b. Allopurinol

c. Ribose phosphate

d. 5-Phosphoribosylpyrophosphate (PRPP)

e. 5-FU

440. In adults, a severe deficiency of vitamin D causes which of the following disorders?

a. Night blindness

b. Osteomalacia

c. Rickets

d. Osteogenesis imperfecta

e. Osteopetrosis

441. A 2-year-old Caucasian girl presents with hair loss, a scaly red skin rash, and exaggerated acidosis after infections. The child is found to have deficiency of biotinidase (MIM*253260), and improves dramatically with biotin therapy. Biotin is involved in which of the following types of reactions?

a. Hydroxylations

b. Carboxylations

c. Decarboxylations

d. Dehydrations

e. Deaminations

442. A 5-year-old girl immigrant from India has had a falloff in growth with arm and leg pains. Her parents attributed this to “growing pains,” but seek evaluation for her growth delay. Examination reveals some wasting of her lower limb muscles with slow fading of pits made by thumb pressure on her shins (pitting edema). Blood tests reveal mild elevations of lactate and pyruvate. The girl is diagnosed with beriberi. Beriberi is caused by a deficiency of which of the following vitamins?

a. Choline

b. Ethanolamine

c. Thiamine

d. Serine

e. Glycine

443. Tryptophan deficiency in diet or disease can cause pellagra, a condition with skin rash on sunlight exposure (photosensitivity), diarrhea, and death. Tryptophan can be a precursor for one part of a compound that is an enzyme cofactor and donor of ADP-ribose that is added to certain histones and DNA repair enzymes (topoisomerases). Which of the following components can be derived from tryptophan, along with its active compound?

a. Biotin, carboxybiotin

b. Intrinsic factor, cobalamin

c. Pantothenic acid, coenzyme A

d. Nicotinamide, nicotinamide adenine dinucleotide

e. Pyridoxine, pyridoxal phosphate

444. A 15-month-old Caucasian girl is hospitalized for failure to gain weight and a chronic rash that is thought due to yeast infection. Evaluation shows the rash is not typical of yeast in that it is distributed beyond the genital area and is worst on the extremities. She also has swelling of the hands and feet (edema) and has lost her hair. Which one of the following is likely to be deficient?

a. Arsenic

b. Lead

c. Zinc

d. Antimony

e. Vanadium

445. A 1-year-old African boy has recently emigrated from Africa and exhibits intermittent diarrhea, pallor (pale skin), extreme tenderness of the bones, “rosary” of lumps along the ribs, nose bleeds, bruising over the eyelids, and blood in the urine. Which of the following is the most likely cause?

a. Deficiency of vitamin C due to a meat-deficient diet during pregnancy.

b. Hypervitaminosis A due to ingestion of beef liver during pregnancy.

c. Deficiency of vitamin C because of reliance on a milk-only diet.

d. Deficiency of vitamin K because of neonatal deficiency and continued poor nutrition.

e. Deficiency of vitamin D due to darker skin pigmentation and poor sun exposure.

446. A 15-month-old African American boy presents with prominent forehead, bowing of the limbs, broad and tender wrists, swellings at the costochondral junctions of the ribs, and irritability. The head is deformable, able to be depressed like a ping-pong ball, while palpation of the joints is very painful. Which of the following treatments is recommended?

a. Lotions containing retinoic acid

b. Diet of baby food containing leafy vegetables

c. Diet of baby food containing liver and ground beef

d. Milk and sunlight exposure

e. Removal of eggs from diet

447. A premature Caucasian male infant of 30 weeks gestation has multiple respiratory complications and remains 2 months in the neonatal intensive care unit. He has received 24 days of total parental alimentation after developing an infection (necrotizing enterocolitis) that necessitates antibiotics and a rested bowel (no feeds) for healing. His nurse reports a plateau in weight gain accompanied by scaly skin on his extremities that is typical of fatty acid deficiency. Which of the following fatty acids would most effectively correct this deficiency?

a. Palmitic acid

b. Linoleic acid

c. Arachidonic acid

d. Oleic acid

e. Eicosatetraenoic acid

448. Ectrodactyly causes missing middle fingers (lobster claw malformation) and exhibits genetic heterogeneity with autosomal dominant and recessive forms. One type of ectrodactyly (split hand-foot malformation) is an autosomal dominant trait (MIM*183600). A grandfather and grandson have this form of ectrodactyly, but the intervening father has normal hands by x-ray. Which of the following terms applies to this family?

a. Incomplete penetrance

b. New mutation

c. Variable expressivity

d. Germinal mosaicism

e. Anticipation

449. Little People of America (LPA) is a support group for individuals with short stature, which conducts many workshops and social activities. Two individuals with achondroplasia (MIM*100800), a common form of dwarfism, meet at an LPA convention and decide to marry and have children. What is their risk of having a child with dwarfism?

a. 100%

b. 75%

c. 50%

d. 25%

e. Virtually 0

450. Osteogenesis imperfecta (MIM*166200) is an autosomal dominant disorder that causes thin, bluish sclerae (whites of the eyes), deafness, and multiple bone fractures. Parents have two children with osteogenesis imperfecta, but themselves exhibit no signs of the disease. Which of the following genetic mechanisms is the most likely explanation for two offspring of normal parents to have an autosomal dominant disease?

a. Variable expressivity

b. Uniparental disomy

c. New mutations

d. Germinal mosaicism in one parent

e. Incomplete penetrance

451. Incontinentia pigmenti (MIM*308300) is an X-linked disorder that is lethal in utero for affected males. The findings vary in females and include pigmented skin lesions, dental abnormalities, patchy areas of alopecia, and mental retardation. Approximately 45% of cases are the result of new mutations. Which of the following descriptions of incontinentia pigmenti is most accurate?

a. X-linked recessive inheritance with spontaneous abortions and few isolated cases

b. X-linked dominant inheritance; 3:1 ratio of females to males in affected sibships

c. X-linked recessive inheritance with spontaneous abortions and many isolated cases

d. X-linked dominant inheritance, 1.5:1 ratio of females to males in affected sibships

e. X-linked dominant inheritance with spontaneous abortions and many isolated cases

452. Two parents are both affected with albinism (MIM*203100 and MIM*203200), but have a normal child. Which of the following terms best describes to this situation?

a. Allelic heterogeneity

b. Locus heterogeneity

c. Variable expressivity

d. Incomplete penetrance

e. New mutation

453. Individuals with achondroplastic dwarfism have about 80% fewer viable offspring than do normal persons, but the incidence of achondroplasia seems to have remained constant for generations. Achondroplasia is an autosomal dominant disorder caused by mutations in the fibroblast growth factor receptor-2. What do these observations imply about the population genetics of achondroplasia?

a. Decreased fitness, negative selection, and relatively high mutation rates

b. Increased fitness, negative selection, and relatively high mutation rates

c. Decreased fitness, positive selection, and relatively low mutation rates

d. Increased fitness, positive selection, and relatively low mutation rates

e. Decreased fitness, positive selection, and relatively high mutation rates

454. A 14-year-old Caucasian adolescent presents to his physician for a sports physical examination that will approve his participation in football. He is noted to have a tall, thin body habitus, loose joints, and arachnodactyly (spider fingers). Ophthalmologic examination reveals lens dislocation. Echocardiogram reveals dilation of the aortic root. A family history reveals that the patient’s parents are medically normal, but that his paternal grandfather and great-grandfather died in their forties with lens dislocation and dissecting aortic aneurysms. A sister is found to have a similar body habitus, dilation of the aortic root, and normal lenses. The physician suspects Marfan syndrome (MIM*154700) and declines to approve his athletic participation until he has cardiology evaluation. Different findings in the boy’s relatives who likely have the same disease are best described by which of the following terms?

a. Pleiotropy

b. Founder effect

c. Variable expressivity

d. Incomplete penetrance

e. Genetic heterogeneity

455. Marfan syndrome is caused by which of the following mechanisms?

a. Mutation that prevents addition of carbohydrate residues to the fibrillin glycoprotein

b. Mutation in a carbohydrate portion of fibrillin that interferes with targeting

c. Mutation that disrupts the secondary structure of fibrillin and blocks its assembly into microfibrils

d. Mutation in a lysosomal enzyme that degrades fibrillin

e. Mutation in a membrane receptor that targets fibrillin to lysosomes

456. The diagnosis of osteogenesis imperfecta (MIM*166200) is most rapidly performed by which of the following?

a. PCR amplification and DNA sequencing of type I collagen gene segments to look for point mutations

b. Analysis of labeled type I collagen chains synthesized in fibroblasts

c. PCR amplification and ASO hybridization to detect particular mutant alleles

d. Clinical evaluation finding fractures, hypermobility, and typical radiographic findings

e. Complete DNA sequencing of the type I collagen chains

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