Longitudinal assessments of the biochemistry and cognitive functioning in three brothers with mannosidosis are reported from the Department of Pediatrics in Human Development; Michigan State University, East Lansing, Michigan. The patients were followed from three or four years of age. The biochemical findings demonstrated profound deficits of leukocyte alpha mannosidase that remained stable over time and were very similar to levels of the same enzyme activity in fibroblasts. Cognitive tests including general intelligence, language, visual spatial skills, and overall adaptive abilities, were generally uniform with no signs of progressive deterioration except for receptive language abilities. When examined initially the patients were mildly retarded. Loss of receptive vocabulary abilities seen above the age of six years may have been related to a conductive hearing loss of 30-40 dB and frequent otitis media. There was a lack of correspondence between the level of enzyme deficiency and the degree of mental dysfunction. Sequential data were obtained for six years for the oldest brother, five years for the middle brother, and four years for the youngest brother. The authors suggest that hearing should be constantly examined to address potential sensory deprivation as it affects cognitive functioning in children with mannosidosis. 
COMMENT. Children with mannosidosis have coarse features, slight hepatosplenomegaly and psychomotor retardation. After two years of age, growth slows down, the tongue enlarges and a lumbar kyphosis and prominent forehead develop. Based on the findings in this study, overall intellectual functioning was low but showed no evidence of progressive deterioration except for receptive language skills.