Characterization of the GALC gene in three Japanese patients with adult-onset Krabbe disease.

Krabbe disease, a neurodegenerative disorder of autosomal recessive inheritance, is caused by mutations in the galactosylceramidase (GALC) gene. However, its clinical manifestations in terms of time of onset and severity are heterogeneous. Thus, elucidation of the relationship of symptoms to the site and type of mutation is important, both for an understanding of the etiology of the disease and for diagnostic purposes. We examined the genomic structure of the GALC gene in three unrelated adult-onset Krabbe disease patients. One patient was homozygous for an Ile66Met mutation. Another patient who appeared to express only one mutated mRNA species was, in fact, a compound heterozygote for an Ile66Met mutation and a nonsense mutation, Tyr354ter. Because the allele with the nonsense mutation was not detectable by mRNA analysis, a rapid degradation of the mRNA caused by premature chain termination was suggested. The third patient who carried two inactiving mutations--Leu618Ser and a second resulting in exon 6 skipping--was also found to carry an intronic mutation, IVS6 + 5G > A. Transfection experiments using a GALC mini-gene proved that this intronic mutation was the cause for the exon 6 skipping.