Silent allele as genetic basis of fucosidosis

SEVERAL individuals have been recognised as having an almost complete deficiency of the lysosomal hydrolase α-L-fucosidase (EC 3.2.1.51) in their tissues and body fluids^1-7. This condition (designated fucosidosis) is associated with the accumulation of fucose-containing glycolipids and glycoproteins in various tissues^1,5. The clinical manifestations include coarse facial features, progressive psychomotor regression, susceptibility to respiratory infections and severe neurological signs, including generalised spasticity. Two distinct forms of fucosidosis (types 1 and 2) have been recognised⁷. Both are characterised by a virtually complete deficiency of α-fucosidase activity when assayed with artificial substrates. Physical and mental deterioration, however, proceeds far more rapidly in type 1 and these patients do not survive beyond early childhood. Type 2 patients can survive to adult life³. Additional features which distinguish the two forms of the disease are the presence, in type 2 only, of the skin lesion, angiokeratoma corporis diffusum, and an elevation in type 1 only, of the NaCl concentration in sweat⁷.