Abstract

CARRASCO SALAS, P; PALMA MILLA, C  and  LOPEZ SILES, J. Determination of survival motor neuron (SMN) genes copy numbers in a sample of healthy population from southern Spain. BAG, J. basic appl. genet. [online]. 2015, vol.26, n.1, pp.5-8. ISSN 1852-6233.

Copy number analysis of the SMN (Survival Motor Neuron) genes in healthy individuals with no history of spinal muscular atrophy (SMA) is important to assess carrier frequency, the frequency of patients with two copies of SMN1 on one chromosome (a factor that could lead to a false-negative result when testing for SMA carriers) and the mechanisms responsible for these chromosomes with two copies of SMN1. We retrospectively analyzed the copy number of SMN1 and SMN2 genes detected in blood samples of 119 gamete donors by Multiplex Ligation- Dependent Probe Amplification (MLPA) assay during the last two years. The number of donors with a heterozygous deletion of exon 7 of SMN1 was 1 in 59 samples (1.7 %). It was estimated that 5.4 % of the studied alleles presented two SMN1 copies. The percentage of individuals with one or zero copies of SMN2 was not statistically different among individuals with two copies of SMN1 (48.1 %) and those with three or four SMN1 copies (63.6 %) (p= 0.327). The frequency of individuals with one copy of SMN1 is low and consistent with previously reported data; therefore, universal screening is not cost-effective, although it could be so in gamete donors. Our results are not in agreement with the hypothesis that the occurrence of gene conversion from SMN2 to SMN1 results in two SMN1 copies on one chromosome.

Keywords : SMN genes; SMA; Carrier; Gene conversion.

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