Spinal muscular atrophy genetic testing experience at an academic medical center.

Approximately 94% of spinal muscular atrophy (SMA) patients lack both copies of SMN1 exon 7. We report our SMA genetic testing experience (total 1281 cases), using SMA linkage analysis (32 families), SMA diagnostic testing by PCR-RFLP (restriction fragment length polymorphism) to detect the homozygous absence of SMN1 exon 7 (and exon 8) (533 cases), and an assay to determine copy number of SMN1 exon 7 (SMN1 gene dosage analysis) (716 cases). SMN1 gene dosage analysis is used for SMA carrier testing as well as for the confirmation of a heterozygous SMN1 deletion in symptomatic individuals who do not lack both copies of SMN1. We conclude that comprehensive SMA testing, including SMN1 deletion analysis, SMN1 gene dosage analysis, and linkage analysis, offers the most complete evaluation of SMA patients and their families.