Invariant exon skipping in the human α-galactosidase A pre-mRNA: A g⁺¹ to t substitution in a 5′-splice site causing Fabry disease

Fabry disease, an inborn error of glycosphingolipid catabolism, results from lesions in the X-linked gene encoding the human lysosomal hydrolase, α-galactosidase A (α-d-galactoside galactohydrolase; EC 3.2.1.22). To detect α-galactosidase A RNA processing or stability defects causing Fabry disease, Northern hybridization analyses were performed with poly(A)⁺ RNA isolated from cultured lymphoblasts from unrelated Fabry hemizygotes. Using a riboprobe complimentary to the normal 1.45-kb α-galactosidase A mRNA, a single 1.25-kb transcript was identified in three classically affected brothers from a Japanese Fabry family. Densitometric analysis revealed that the 1.25-kb transcripts were present at 50 to 60% of normal amounts. RNase A analysis identified a deletion of about 200 bp that appeared to include the entire 198 bp of exon 6. Amplification and direct sequencing of a genomic region containing exon 6 from an affected hemizygote revealed a g⁺¹ to t transversion in the invariant gt consensus 5′-splice site of intron 6, which resulted in the deletion of the entire exon 6 sequence. This novel splicing lesion causing Fabry disease is the first g⁺¹ to t transversion of a mammalian 5′-splice site that consistently eliminates the preceding exon.