A 15-year-old boy has been diagnosed with retinitis pigmentosa, peripheral polyneuropathy, and cerebellar ataxia. Analysis of his cerebrospinal fluid indicated a high protein content but no elevation of cell number. Atelling clinical finding was a high level of serum phytanic acid. These findings are indicative of which of the following disorders?
(A) carnitine palmitoyltransferase I deficiency
(B) fragile X syndrome
© MCAD deficiency
(D) Refsum disease
(E) rhizomelic chondrodysplasia punctata
Explanation
(D) Refsum disease is the result of defects in the oxidation of phytanic acid, a lipid requiring an alpha-oxidation pathway. As a consequence, phytanic acid accumulates in the blood and tissues. The hallmark symptoms of the disease are retinitis pigmentosa, cerebellar ataxia, chronic polyneuropathy, and an elevation in protein in the cerebrospinal fluid with no increase in cell count. Adeficiency in carnitine palmitoyltransferase I (choice A) primarily affects the liver and results in reduced fatty acid oxidation and ketogenesis. Fragile X syndrome (choice B) is the most common form of heritable mental retardation worldwide. MCAD deficiency (choice C) is one of most frequently inherited defects in metabolism. Clinical crisis is characterized by an infant presenting with episodes of vomiting and lethargy, seizures, and coma associated with a period of fasting. On presentation, the infant may be comatose and blood glucose will be low with low to no ketones in urine. RCDP(choice E) is caused by a disorder in peroxisome biogenesis. Rhizomelia refers to striking shortening of the proximal limbs. Patients also have severely disturbed endochondral bone formation. In addition, RCDP patients have profound psychomotor retardation.