Molecular analysis of acid ceramidase deficiency in patients with Farber disease

Farber disease is a rare, autosomal recessively inherited sphingolipid stor age disorder due to the deficient activity of lysosomal acid ceramidase, le ading to the accumulation of ceramide in cells and tissues. Here we report the identification of six novel mutations in the acid ceramidase gene causi ng Farber disease: three point mutations resulting in single amino acid sub stitutions, one intronic splice site mutation resulting in exon skipping, a nd two point mutations also leading to occasional or complete exon skipping . Of interest, these latter two mutations occurred in adjacent nucleotides and led to abnormal splicing of the same exon. Expression of the mutated ac id ceramidase cDNAs in COS-1 cells and subsequent determination of acid cer amidase residual enzyme activity demonstrated that each of these mutations was the direct cause of the acid ceramidase deficiency in the respective pa tients. In contrast, two known polymorphisms had no effect on acid ceramida se activity. Metabolic labeling studies in fibroblasts of four patients sho wed that even though acid ceramidase precursor protein was synthesized in t hese individuals, rapid proteolysis of the mutated, mature acid ceramidase occurred within the lysosome. Hum Mutat 17:199-209, 2001. (C) 2001 Wiley Li ss, Inc.