Fumarate hydratase deficiency in monozygotic twins.

Monozygotic twins with fumarate hydratase deficiency presenting with profound hypotonia and developmental delay are reported. This rare organic aciduria has been previously described in random case reports, although, to our knowledge, these are the first reported monozygotic twins and gene testing revealed a novel mutation in both. During their course, one of the twins also developed acute pancreatitis, which has not been previously described in association with this particular organic aciduria.