The biochemical diagnosis of lysosomal storage diseases--a review of five years experience.

The inherited lysosomal storage diseases are a distinct group of inborn errors of metabolism characterised by deficiencies in specific lysosomal enzymes. As many as 40 such disorders have now been described in man. We have measured the activities of up to 16 lysosomal acid hydrolases in plasma and/or extracts of leucocytes and cultured skin fibroblasts from 198 patients referred from throughout Ireland. These 16 assays allowed the biochemical diagnosis of 20 lysosomal storage diseases. Activities were compared with reference ranges to determine homozygotes and heterozygotes. Of the 44 patients with positive results, 15 were diagnosed as being homozygous for a specific lysosomal enzyme deficiency, 4 were identified as having multiple enzyme deficiencies (mucolipidosis Type II/I-cell disease) and 25 had heterozygote (carrier) enzyme levels. Of the latter, 24 were either parents (obligate heterozygotes) or siblings of homozygotes and one was a heterozygote for the X-linked recessively inherited Fabry's disease.