Human beta-mannosidosis is an inherited lysosomal storage disorder des
cribed in only seven families. We present a further case in a black Af
rican 14-year-old boy with severely deficient beta-mannosidase activit
y, bilateral thenar and hypothenar amyotrophy, electrophysiologically
demonstrable demyelinating peripheral neuropathy, and cytoplasmic vacu
olation of skin fibroblasts and lymphoid cells. The clinical and bioch
emical features of our patient are compared to those of previously rep
orted patients.