Late-onset form of partial N-acetylglutamate synthetase deficiency.

A 13-month-old female presented with neurological deterioration of 1 month duration and hyperammonaemia. N-acetylglutamate synthetase activity in the liver was reduced to 33% of the control. A male cousin and a female sister had died following a similar clinical course. This is the first report of late-onset N-acetylglutamate synthetase deficiency. An autosomal-recessive mode of inheritance is suggested.