Gene conversion events in adult-onset spinal muscular atrophy


Aldo Quattrone, MD, Cattedra e U.O. di Neurologia, Policlinico Materdomini, Via T. Campanella, 88100 Catanzaro, Italy
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Objective – To investigate the possible occurrence of a conversion event in three patients with adult-onset spinal muscular atrophy (SMA) type IV, which represents the mildest form within the spectrum of the SMA phenotype.

Material and methods – We observed three patients with adult onset SMA and apparent isolated deletion of telomeric survival motor neuron (SMN1) exon 7. To distinguish between a deletion and a sequence conversion event of exon 7, these patients were analyzed in greater detail by a simple PCR-based assay.

Results – Analysis by DdeI digestion showed products for both telomeric and centromeric copies of exon 8. These findings indicated a gene conversion event as the site for primer R111 was retained at least in one of two alleles.

Conclusions – These results provide first evidence that a conversion event may be also associated with adult-onset SMA, and further support the notion that a gene conversion event is usually associated with a milder SMA phenotype and a later onset of disease.