a. The print-out highlights a deletion of chromosome 16 that is described by nomenclature indicating a reduced dosage (X 1 instead of normal 2) and the precise base pairs missing.

b. The print-out highlights a deletion of chromosome 16 that is described by nomenclature indicating a normal dosage of that chromosome region (X 1 instead of X 3).

c. The abnormal result seems to be in error, since another part of the report documents a normal routine karyotype.

d. The abnormal result provides definitive proof that the child has autism.

e. The laboratory should not have described the result as abnormal until parental analyses are completed.

307. A severe birth defect syndrome called retinoic acid embryopathy (MIM*243440) is caused by medications such as isotretinoin (Accutane) when taken by pregnant women for treatment of acne. Retinoic acid and steroid hormones are group I signals that cross the cell membrane to interact with cytosolic or nuclear receptors. Which of the structural domains of such receptors would interact with retinoic acid?

a. Response elements

b. Antirepressor domains

c. Transcription-activating domains

d. Ligand-binding domains

e. DNA-binding domains

308. Two boys with mental disability are found to have mutations in a gene on the X chromosome that has no homology with globin genes. Both are also noted to have deficiency of α-globin synthesis, causing imbalance of globin chains and the severe anemia and skeletal changes of α-thalassemia plus mental retardation (MIM*301040). Which of the following is the best explanation for their phenotype?

a. The mutation disrupted an enhancer for an α-globin pseudogene.

b. The mutation disrupted an X-encoded transcription factor that regulates the α-globin loci.

c. There is a second mutation that disrupts an enhancer near the α-globin gene.

d. There is a DNA rearrangement that joins the mutated X-chromosome gene with an α-globin gene.

e. There is a second mutation that disrupts the promoter of an α-globin gene.

309. The presence of which of the following structural arrangements in a protein strongly suggests that it is a DNA-binding, regulatory protein?

a. α helix

b. β bend

c. β sheet

d. Triple helix

e. Zinc finger

310. A 21-year-old Caucasian male college student presents to the health clinic with symptoms of increased urination (polyuria), avid thirst and water drinking (polydipsia), and weight loss without dieting. Significant in the family history is his father’s death at age 42 of, what was said to be “acute diabetes.” His father’s sister and a paternal aunt also have diabetes, described as adult onset or type II. Laboratory evaluation reveals increased glucose in blood (hyperglycemia), urine (glucosuria), and urinary ketones. However, Western blotting of insulin species shows normal amounts of protein with a higher molecular size than usual. Which of the following is the most likely explanation?

a. Defective processing of proinsulin to insulin, causing decreased insulin action and diabetes mellitus

b. Defective insulin-like growth factors that must act in concert with insulin

c. Defective insulin receptors with reduced insulin action

d. Progressive fibrosis of pancreatic β-cells, leading to insulin deficiency

e. Defect in processing of a pituitary hormone that contains the insulin peptide

311. The functions of many enzymes, membrane transporters, and other proteins can be quickly activated or deactivated by phosphorylation of specific amino acid residues catalyzed by enzymes called what?

a. Cyclases

b. Kinases

c. Phosphatases

d. Proteases

e. Zymogens

312. A 28-year-old African American female and her husband have serial ultrasound studies during the last month of pregnancy because their fetus has short limbs. Their maternal-fetal medicine specialist suspects the diagnosis of achondroplasia (MIM*100800), a moderate form of dwarfism caused by mutation within the receptor domain of the fibroblast growth factor-3 receptor (FGFR3) gene. Unfortunately, the findings after birth suggest a more severe dwarfism with very short limbs and a small chest that does not allow adequate oxygenation. After death, a mutation changing lysine to glutamine at position 650 in the FGFR3 tyrosine kinase domain is found that is consistent with the severe phenotype called thanatophoric (death-loving) dwarfism (MIM*187600). Both of these phenotypes exhibit autosomal dominant inheritance, requiring one abnormal allele at the FGFR3 locus on chromosome 4. Which of the following is a likely molecular explanation for their difference in severity?

a. Mutation at the tyrosine kinase domain rather than the saturable ligand-binding domain will have more severe effects.

b. Signal transduction through tyrosine phosphorylation is an enzyme-mediated process requiring two abnormal alleles for phenotypic effects (recessive inheritance).

c. Fibroblast growth factor-3 is a large molecule and cannot achieve saturating concentrations that would overcome receptor mutations.

d. Binding of ligands to receptors is a linear process that is independent of ligand or receptor concentration.

e. Binding of tyrosine phosphate to FGFR3 is an allosteric effect.

313. Hormones such as insulin or glucagon act at cell membranes to stimulate release of “second messengers” such as cyclic AMP that effect cellular responses. Which of the following options best describes their mechanism of action?

a. Soluble hormones enter channels within symmetric membranes Structure A

b. Soluble hormones react with surface receptors on asymmetric membranes

c. Soluble hormones within micelles fuse with symmetric membranes

d. Insoluble hormones diffuse through membranes to the cytosol

e. Insoluble hormones adhere to desmosomes between cells

314. A 4-year-old Caucasian girl is evaluated for rapid growth and obesity that has developed despite apparently normal food intake. Physical examination shows an unusual fat distribution with a pad over her neck and multiple stretch marks (striae). Based on the probable diagnosis of Cushing syndrome, which of the following would be found by laboratory testing?

a. Decreased production of epinephrine

b. Excessive production of epinephrine

c. Excessive production of vasopressin

d. Excessive production of cortisol

e. Decreased production of cortisol

315. A 3-day-old African American girl is noted to have a narrow distance between the eyes (hypotelorism), malformed nose with a single nostril (proboscis), and a midline cleft lip. These facial changes suggest a brain malformation called holoprosencephaly where the forebrain and related structures fail to develop. The child is noted to have decreased urine output and hypernatremia (high serum sodium concentration). Which of the following hormones is implicated?

a. Cortisol

b. Insulin

c. Vasopressin

d. Glucagon

e. Aldosterone

316. A 22-year-old Caucasian male college student becomes extremely tired after playing golf and seeks evaluation from the student health service. Past medical history reveals normal puberty and genital development. He recalls previous episodes of fatigue that he attributes to dehydration, and his physician obtains a serum glucose of 55 mg/dL (normal 75-105) and serum electrolytes showing Na 142 mEq/L (normal 133-146), K 2.2 mEq/L (normal 3-5.1), Cl 104 mEq/L (normal 98-105), and HCO₃ 23 mEq/L (normal 22-28). Which of the following disorders are most likely?

a. Cushing disease with Androstenedione deficiency

b. Cushing disease with 17α-hydroxyprogesterone deficiency

c. Congenital adrenal hyperplasia with estrone deficiency

d. Addison disease with 18-hydroxylase deficiency

e. Addison disease with testosterone excess

317. A 7-month-old Hispanic boy is evaluated for asymmetric skull shape and possible hearing problems. Physical examination reveals a prominent forehead (tower skull) with prominent eyes (exophthalmos) and ridges over his coronal sutures. Premature fusion of the coronal sutures (craniosynostosis) is suspected as part of Crouzon syndrome (MIM*123500), a condition caused by mutations in the fibroblast growth factor receptor-2. Several conditions with disproportionate skeletal growth (dwarfism) or craniosynostosis are caused by mutations in fibroblast growth factors or their receptors. Fibroblast growth factor belongs to which of the following hormone groups?

a. Membrane-soluble hormones interacting with nuclear receptors

b. Membrane-soluble hormones interacting with cytoplasmic receptors

c. Receptor-binding hormones activating calcium/phosphatidyl inositol messengers

d. Receptor-binding hormones activating cAMP/cGMP messengers

e. Receptor-binding hormones activating kinase cascades

318. A 50-year-old Caucasian male presents to his physician because of anxiety attacks accompanied by profuse sweating and heart palpitations. His physician documents a high blood pressure of 175/110 (hypertension) and orders ultrasound studies that show an adrenal tumor called pheochromocytoma. The male has also noted weight loss and fatigue over the past month when the attacks began. Knowing that pheochromocytoma releases epinephrine from the adrenal medulla, alteration of which of the following metabolic processes best explains symptoms of decreased energy and weight loss?

a. Glycolysis

b. Lipolysis

c. Gluconeogenesis

d. Glycogenolysis

e. Ketogenesis

319. A 19-year-old African American male college student presents to his physician complaining of fatigue, weight loss, inability to concentrate, and occasional fainting spells. He also has noted a slight brown pigmentation to his skin despite no sun exposure. His physician suspects Addison disease, a multifactorial disorder that causes dysfunction of the adrenal cortex. Which of the following hormones is most likely deficient in Addison disease?

a. ACTH

b. Norepinephrine

c. Aldosterone

d. Testosterone

e. Epinephrine

320. The 4-ring structure typical of steroids would be found in which of the following hormones?

a. Adrenocorticotropin

b. Aldosterone

c. Epidermal growth factor

d. Insulin

e. Insulin-like growth factor

321. A 15-month-old African American boy has recently been weaned from breast-feeding to whole milk in addition to a balanced diet of table food. His pediatrician refers him to endocrinology because he is noted to have increasing outward bowing of the legs (genu valgum) and thickened, somewhat tender wrists. Which of the following mechanisms is likely operating in this child?

a. Decreased calcium in the diet

b. Decreased conversion of cholesterol intermediates to previtamin D in the skin

c. Decreased conversion of skin previtamin D to blood cholecalciferol

d. Decreased conversion of cholecalciferol to calcidiol in liver

e. Decreased conversion of calcidiol to calcitriol in kidney

322. An unfortunate complication of long-term diabetes mellitus is the occurrence of heart attacks and gangrene of the extremities. Which of the following is the most likely cause?

a. Decreased glucose availability to liver cells

b. Decreased glucose availability to extrahepatic tissues

c. Increased catecholamine synthesis

d. Decreased catecholamine synthesis

e. Decreased glucose concentrations in vascular epithelium

323. Diabetes mellitus is caused by insulin deficiency or resistance with decreased import of glucose into extrahepatic tissues. Type I diabetes with earlier onset often follows a viral infection with inflammation of the pancreatic β-cells, while later onset type II diabetes is strongly associated with obesity. Each type exhibits genetic predisposition with a 40% to 50% concordance rate in monozygous twins and clustering in families. Diabetes mellitus is best described as which of the following types of disorders?

a. Congenital disorder

b. Multifactorial disorder

c. Mendelian disorder

d. Sporadic disorder

e. Sex-limited disorder

324. As exemplified by HLA-DQβ haplotypes in type I diabetes mellitus, an individual’s HLA status may be relevant to genetic counseling for certain multifactorial diseases. The relation of HLA haplotypes to disease and the use of this information in genetic counseling are referred to as which of the following?

a. Genetic linkage and the frequency of recombination

b. Allele association and risk modification

c. Positional cloning and gene isolation

d. Gene mapping and gene segregation

e. Genotyping and phenotypic correlation

325. A child has ambiguous genitalia including an apparent small phallus and scrotum. The child’s DNA hybridizes to probes from the sex-determining region of the Y (SRY). Based on the clinical findings and dot-blot analysis, which of the following terms applies?

a. Female pseudohermaphroditism

b. Male pseudohermaphroditism

c. True hermaphroditism

d. XY female

e. XX male

326. A newborn with ambiguous genitalia and a 46,XY karyotype develops vomiting, low serum sodium concentration, and high serum potassium. Which of the following proteins is most likely to be abnormal?

a. 21-Hydroxylase

b. An ovarian enzyme

c. 5β-Reductase

d. An androgen receptor

e. A testicular enzyme

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