The frequency of two common disease-associated mutations in the arylsulphatase A (ASA) gene, and of a mutation causing ASA pseudodeficiency, have been established in metachromatic leukodystrophy patients diagnosed in our laboratory. A total of 37 mutant genes have been analysed. The G→A change destroying the splice donor site of exon 2 is generally associated with more severe disease and was found in 43.2% of mutant ASA genes. The C→T transition causing a proline to leucine substitution at position 426 in exon 8 (P426→L) is associated with later onset disease, and was found in 16.2% of mutant genes. The A→G transition leading to loss of a polyadenylation signal associated with ASA pseudodeficiency was present at a frequency of 7.5% in the patients and heterozygotes studied.
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