Sir.—I was greatly interested to read the letter from abroad on "Mucolipidosis IV" (ML IV) by Dr Laron in the Journal (1981;135:975).
With regard to the metabolic defect of this disorder, I would point out that an abnormal ganglioside accumulation has been described not only in cultured skin fibroblasts1 but also in the white matter.2 In addition, a second component accumulating in ML IV was described as acid mucopolysaccharide,1 but it was suggested that it may be hyaluronic acid.3
Although the enzyme deficiency is not yet known, a ganglioside neuraminidase deficiency has been reported.4
Finally, prenatal diagnosis of ML IV has been established by electron microscopy. Abnormal storage bodies (membranous cytoplasmic bodies) in cells grown from cultures of fetal amnion and typical changes in the corneal epithelium were disclosed by ultrastructural investigations.5
I would also emphasize that corneal clouding, present even at birth,