Follow-up of language and cognitive development in patients with mannosidosis.

Three brothers with mannosidosis were assessed both biochemically by levels of enzyme activities and developmentally by serial testing of language and cognitive development. The findings indicated that while the leukocyte enzyme activity of alpha-mannosidase was exceptionally low, only mild intellectual deficits were present that did not progress during a two-year follow-up. These results do not substantiate the expected relationship between the severities of enzyme deficiency and developmental delays. Language and cognitive deficits appeared uniform with no areas of strengths or weaknesses. Deficits in development did not progress during a two-year follow-up.