High cognitive outcome in an adolescent with mut(-) methylmalonic acidemia

Methylmalonic acidemia is an inborn error of metabolism known to be a cause of ketoacidosis and mental retardation. The less severe mut(-) form of the disorder, however, has been described with only mild to moderate cognitive deficits or, rarely, with normal neurodevelopment in asymptomatic cases. N evertheless, there has been no detailed documentation of long-term neuropsy chological function in the mut- form and relatively few IQ scores. We perfo rmed longitudinal developmental and neuropsychological assessments on a gir l with symptomatic mut- methylmalonic acidemia whose biochemical abnormalit ies were in the moderately severe range and who had had recurrent episodes of ketoacidosis, At almost 12 years of age, her full scale IQ on the Wechsl er Intelligence Scale, third edition, was 129 with very superior and superi or scores on nonverbal and verbal skills, respectively. On the National Ach ievement Test she scored above the 99th percentile in the Basic Battery and is considered to be a gifted student. This outcome suggests that the spect rum of cognitive attainment in mut- methylmalonic acidemia is wide and that even a moderate degree of biochemical severity with ketoacidotic episodes may not result in cognitive deficit. (C) 2000 Wiley-Liss, Inc.