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A 5-year-old child has a history of erythema, swelling, and crying within minutes of sun exposure, as well as red teeth and urine. A mutation in which enzyme could account for this disorder?

A. Porphobilinogen deaminase

B. Uroporphyrinogen decarboxylase

C. Coproporphyrinogen oxidase

D. Protoporphyrinogen oxidase

E. Ferrochelatase

B. While heterozygous mutation in uroporphyrinogen decarboxylase can lead to porphyria cutanea tarda, homozygosity causes hepatoerythropoietic porphyria, which can present with the features described. These features are also seen in congenital erythropoietic porphyria, (Gunther disease); however, uroporphyrinogen III synthase was not an answer choice.

A patient presents with numerous itchy, reddish-yellow papules over his buttocks and dorsal arms. What condition would not be a potential cause?

A. Apolipoprotein C2 mutation

B. Diabetes

C. Oral retinoid therapy

D. Hyperthyroidism

E. Lipoprotein lipase mutation

D. Eruptive xanthomas come from elevated serum TG and have been associated with types I, IV, and V familial hypercholesterolemia, diabetes, oral retinoid therapy, and hypothyroidism. Hyperthyroidism is associated with warm, moist skin, thin hair and nails, and pretibial myxedema.

Which is the most common cutaneous manifestation of diabetes?

A. Scar-like macule above the ankle

B. Yellow, indurated plaque with a red rim on the shin

C. Painless ulcer on the plantar metacarpophalangeal (MP) joint

D. Blister on the dorsal foot

E. Dark, velvety thickening of the axilla

A. Diabetic dermopathy is the most common cutaneous sign of diabetes, occurring in up to half of patients as small, atrophic, reddish-brown macules, commonly on the lower extremities.

In which of the following genes does mutation not characteristically lead to neuropsychiatric disturbances?

A. Copper transporter P-type ATPase 7B

B. Porphobilinogen deaminase

C. Homogentisic acid oxidase

D. Phenylalanine hydroxylase

E. Cystathionine β-synthetase

C. Alkaptonuria is characterized by dark urine (if pH >7), kidney stones, and arthritis, but not neuropsychiatric disturbance, unlike Wilson disease (ATP7A), AIP (homogentisic acid oxidase), PKU (phenylalanine hydroxylase), and homocystinuria ...

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