Analysis of the SMN and NAIP genes in slovak spinal muscular atrophy patients

We identified homozygous absence of exon 7 of the telomeric copy of the survival motor neuron gene (telSMN) in 88.4% (38/43) of spinal muscular atrophy (SMA) patients from Slovakia. Additional deletions within the neuronal apoptosis inhibitory protein (NAIP) gene were found in 38.5% of type I, 12.5% of type II and never in type III SMA patients. Neither the SMN nor the NAIP gene was deleted in 81 healthy relatives and 25 controls tested. In one family, pseudodominant inheritance was identified. Both the type III SMA father and type II SMA son carried the homozygous deletion of the telSMN gene. One SMA I patient showed an SMN hybrid gene, probably created by intrachromosomal deletion. In two haploidentical type II SMA sibs, the telSMN exon 7 was absent on one chromosome, while the other carried an A-->G transition 96 bp upstream of exon 7 of the telSMN gene, a potential disease-causing mutation in these patients.