Neurol Genet 2020 Oct 1;6(5):e505. Epub 2020 Sep 1.
Department of Neurology (R.H.M., C.M., G.J.P., A.M.S.S., D.J.F.S., F.K., U.C.R., E.Z.); Department of Pathology (L.K., A.T.D., E.A.Z.), Faculdade de Medicina da Universidade de São Paulo (FMUSP); Departamento de Pediatria e Neuropediatria (J.G.-G., A.C.M.L.M., G.P.C.S.), Hospital das Clínicas da Universidade Federal de Minas Gerais, Belo Horizonte; Departamento de Neurologia - UNIFESP (A.S.B.O., P.V.S.S., W.B.V.R.P., E.A.G., I.B.F.), São Paulo; Departamento de Pediatria, Seção de Neurologia Infantil - UFRJ (F.N., A.P.Q.C.A.), Rio de Janeiro; Departamento de Neurologia (W.M., P.J.T.), FMUSP-RP, Ribeirao Preto; Mendelics Análise Genômica (M.D.O.R., J.P.K., F.P.M., F.K.), São Paulo; Serviço de Neurologia (J.A.M.S.), Hospital de Clinicas de Porto Alegre, Universidade Federal do Rio Grande do Sul, UFRGS, Porto Alegre; Unidade de Neurologia Infantil (M.M.B.), Hospital de Clinicas de Porto Alegre; Serviço de Genética Médica (J.A.M.S., M.L.S.-P., A.C.B.-F.), Hospital de Clinicas de Porto Alegre; UFRGS, Porto Alegre; Departamento de Bioquímica - UFRGS (M.L.S.-P.), Porto Alegre; Hospital Maria Lucinda (V.L., R.N.F.), Recife; Hospital Infantil Joao Paulo II (A.V.S.B.), Fundação Hospitalar de Minas Gerais, Belo Horizonte; Escola Bahiana de Medicina e Saúde Pública (M.C.M.-C.), Salvador; Hospital Infantil Albert Sabin (A.L.S.P.), Universidade Estadual do Ceará, Fortaleza; and Departamento de Neurologia (L.S.S., M.C.F.), Unicamp, Campinas, Brazil.
Objective: The aim of the study was to report the proportion of homozygous and compound heterozygous variants in the survival motor neuron 1 () gene in a large population of patients with spinal muscular atrophy (SMA) and to correlate the severity of the disease with the presence of specific intragenic variants in and with the copy number.
Methods: Four hundred fifty Brazilian patients with SMA were included in a retrospective study, and clinical data were analyzed compared with genetic data; the copy number was obtained by multiplex ligation-dependent probe amplification and pathogenic variants in by next-generation sequencing.
Results: Four hundred two patients (89.3%) presented homozygous exon 7- deletion, and 48 (10.7%) were compound heterozygous for the common deletion in one allele and a point mutation in the other allele. Recurrent variants in exons 3 and 6 (c.460C>T, c.770_780dup and c.734_735insC) accounted for almost 80% of compound heterozygous patients. Another recurrent pathogenic variant was c.5C>G at exon 1. Patients with c.770_780dup and c.734_735insC had a clinical phenotype correlated with copy number, whereas the variants c.460C>T and c.5C>G determined a milder phenotype independently of the copies.
Conclusions: Patients with specific pathogenic variants (c.460C>T and c.5C>G) presented a milder phenotype, and the copy number did not correlate with disease severity in this group.