COBALAMIN C DISEASE AND EXPANDED NEWBORN SCREENING: THE CALIFORNIA EXPERIENCE.

Abstract

Cobalamin C (cblC) disease is the most common inborn error of vitamin B12 metabolism. Patients have elevated methylmalonic acid (MMA) and homocysteine and typically have a poor prognosis. Common features include mental retardation, nystagmus, pigmentary retinopathy, and neurodegeneration. Treatment includes protein restriction and hydroxocobalamin, betaine, carnitine, and folic acid supplementation. California initiated expanded newborn screening (NBS) in July 2005. Since that time, there have been 10 cases of cblC disease confirmed by fibroblast complementation analysis and/or biochemical studies, resulting in a surprisingly high estimated prevalence of 1 in 60,000. An additional three newborns have been identified in Northern California in whom confirmatory studies are pending. Because 8 of 10 cases are Hispanic, we estimate the prevalence in the Hispanic population to be 1 in 37,000. In the confirmed cases, initial NBS results showed an elevated C3 level ranging from 6.5 to 13.1 μmol/L and an elevated C3/C2 ratio ranging from 0.29 to 0.45 (reference range