Alternative splicing in the alpha-galactosidase A gene: increased exon inclusion results in the Fabry cardiac phenotype.
Fabry disease is an inborn error of glycosphingolipid catabolism, resulting from deficient activity of lysosomal alpha-galactosidase A (alpha-Gal A). A rare alternative splicing that introduces a 57-nucleotide (nt) intronic sequence to the alpha-Gal A transcript from intron 4 of the gene has been identified. In addition, a novel midintronic base substitution that results in substantially increased alternative splicing has been identified in a patient with Fabry disease who has the cardiac variant phenotype. The sequence of the patient's intron 4 contains a single G-->A transversion at genomic nt 9331 (IVS4+919 G-->A ), located at the minus sign4 position of the 3' end of the intronic insertion (nts 9278--9334 in the genomic sequence). Minigene constructs containing the entire intron 4 sequence with G, A, C, or T at nt 9331 within an alpha-Gal A complementary DNA expression vector were prepared and expressed in COS-1 cells. Whereas transfection of the G or T minigenes transcribed predominantly normal-sized transcripts, the transfection of the A or C minigenes produced a large amount of the alternatively spliced transcript. These results suggest that the G-->A mutation, within an A/C-rich domain, results in increased recognition of the alternative splicing by an A/C-rich enhancer-type exonic splicing enhancer. The intronic mutation was not observed in 100 unrelated unaffected men but was present in 6 unrelated patients with cardiac Fabry disease. Reverse-transcriptase polymerase chain reaction of total RNA of various normal human tissues revealed that the alternatively spliced transcript was present in all of the samples, and especially at a higher ratio in the lung and muscle. The normal transcript was present in the patients' lymphoblasts and resulted in approximately 10% residual enzyme activity, leading to a cardiac phenotype of Fabry disease.
Ishii
Satoshi
S
Department of Human Genetics, Mount Sinai School of Medicine, Fifth Avenue at 100th Street, New York, NY 10019, USA.
Nakao
Shoichiro
S
Minamikawa-Tachino
Reiko
R
Desnick
Robert J
RJ
Fan
Jian-Qiang
JQ
D017398:Alternative Splicing / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D005091:Exons / Q000235:genetics*; D000795:Fabry Disease / Q000150:complications / Q000201:enzymology / Q000235:genetics* / Q000503:physiopathology*; D006331:Heart Diseases / Q000150:complications / Q000201:enzymology / Q000235:genetics* / Q000503:physiopathology*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D000519:alpha-Galactosidase / Q000737:chemistry / Q000235:genetics*
D012333:RNA, Messenger; D000519:alpha-Galactosidase