A 7-year-old boy is being examined to determine the cause of his severe skin blistering upon mild exposure to the sun. His parents also note that when he doesn't flush the toilet after urinating, his urine turns a very dark reddish-orange. Physical examination shows the child has darkly stained teeth and fine hairs over his entire face, arms, and legs. Blood and urine studies show high levels of uroporphyrinogen I in both and high coproporphyrinogen I in the blood. Which of the following most likely explains the signs and symptoms in the child?

Question

Quizplus · Accepted Answer

The symptoms and laboratory findings are consistent with congenital erythropoietic porphyria, which is caused by a deficiency in uroporphyrinogen III synthase.  A deficiency in uroporphyrinogen synthase III (the fourth enzyme of heme synthesis) results in the accumulation of its substrate, hydroxymethylbilane. Hydroxymethylbilane can nonenzymatically cyclize forming uroporphyrinogen I and coproporphyrinogen I. These heme biosynthetic by-products turn the urine red to reddish-orange and when deposited in the teeth turn them yellow to reddish brown. Accumulation of these by-products in the skin renders it extremely sensitive to sunlight causing ulceration and disfiguring scars. Increased hair growth (hypertrichosis) is also a symptom of the porphryias leading to appearance of fine hairs over the entire face and on the extremities.

A 7-Year-Old Boy Is Being Examined to Determine the Cause