Résumé :
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In this report we summarize the results of the work on the phenotype, epidemiology and molecular genetics of Polish cases of spinal muscular atrophy caused by SMN1 mutations.Biallelic loss of exon 7 of the SMN1 gene, the most frequent SMA mutation, was identified in 96.5% of patients meeting the diagnostic criteria for SMA. Acute SMA predominated among the diagnoses, amounting to 69% of all cases. SMA2 and SMA3 were diagnosed in 12% and 19% of cases, respectively. In four cases, asymptomatic biallelic loss of the SMN1 gene was identified. The distribution of the number of SMN2 gene copies the most important SMA phenotype modifier, was similar to that noted in data published previously, though it was more frequent for three copies of SMN2 to be observed in the severe form. In SMA1, one or two SMN2 copies were observed in 59% of cases and three in 41% of cases. In SMA2, 84% of patients had 3 copies of the gene. 4 SMN2 copies were noted in about 53% of SMA3 patients, and there was 1 patient with a mild form of the disease - in which 5 copies of SMN2 were found. The prevalence of the SMN1 gene-deletion carrier state was estimated at 1 in 35 people (17/600), while the incidence of SMA stands at 1 per 7,127 in Warsaw and 1 per 9,320 persons across Poland.Our study therefore indicates that spinal muscular atrophy could be a more frequent disease than is predicted by the epidemiological data regarding diagnosed cases. It is thus probable that chronic forms of SMA go underdiagnosed in Poland. In summary, the number of SMN2 copies can generally be seen to correlate with SMA phenotype, though this should not be used as a primary prognostic factor.
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