Identification of T274I mutation in the SMN1 gene in a patient with spinal muscular atrophy

: Proximal spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder characterised by degeneration of motor neurones in the spinal cord. The symptoms of the disease are determinated by mutations of SMN1 gene. About 98% of SMA patients show homozygous absence of exon 7 SMN1 gene, the rest carry small intragenic mutations. Molecular analysis of the presence of exon 7 SMN1 gene deletion is considered as the screening test for SMA. We present a case report of a 9 years old girl with progressive muscular weakness of limbs and trunk. Clinical examination followed by electromyography and muscle biopsy was interpreted as a diagnostic of SMA 3. Molecular analysis did not reveal deletion of exon 7 SMN1 gene. Extended molecular diagnostics using direct sequencing showed missence mutation T2741. Thus, the absence of homozygous deletion of exon 7 SMN1 gene does not exclude SMA diagnosis. All patients fulfilling the diagnostic criteria for SMA, as defined by the International SMA Consortium, without deletion of exon SMN1 gene, should be analysed using direct sequencing.