[ 14C]methylamine accumulation in cultured human skin fibroblasts — a biochemical test for lysosomal storage and lysosomal diseases

Incorporation of the lysosomotropic amine [ 14C]methylamine by fibroblasts cultured from patients with lysosomal storage diseases and from controls was used to estimate the size of the lysosomal compartment. All cell lines from patients with infantile and juvenile forms of mucopolysaccharidoses, mucolipidoses and oligosacharidoses showed markedly increased radioactivity compared with the normal range of controls. In cells from patients with sphingolipidoses and adult forms of storage diseases, however, methylamine accumulation was not significantly increased. Experimentally induced lysosomal storage by enzyme inhibitors (leupeptin, suramin) also caused increased methylamine accumulation. When the lysosomal pH was determined with fluorescein isothiocyanate-dextran, it was in the range of normal controls (pH 4.7–5.0) in patients cells. Thus, [ 14C]methylamine accumulation should depend on the volume rather than differences in acidity of the lysosomal compartment and be a measure of its eventual pathological enlargement. We conclude that the determination of [ 14C]methylamine accumulation in fibroblasts provides a valuable tool in the screening for a variety of lysosomal storage disorders.