Genetic analysis of a case of infant spinal muscular atrophy type 1c / 中国综合临床

Objective:To summarize the genetic characteristics of a case of spinal muscular atrophy type 1c.Methods:The case data of a child with spinal muscular atrophy type 1c was retrospectively analyzed, and the genetic analysis and literature review were carried out.Results:The patient, male, started at the age of 2 months, and showed gross motor development backwardness and low muscular tension. Multiplex connection probe amplification technique showed that the child had homozygous deletion mutation in exon 7-8 of SMN1 gene, and there was duplicate mutation in exon 7-8 of SMN2 gene. The number of copies of exon 7/8 was 3/3. His father was a heterozygous deletion carrier of SMN1 gene, and there was homozygous mutation in exon 8 of SMN2 gene. The number of copies of exon 7/8 was 2/3. His mother did not find abnormal exons of SMN1 gene, and the number of copies of exon 7/8 of SMN2 gene was 1/1.Conclusion:Spinal muscular atrophy lacks specific manifestations in the early stage, and the diagnosis mainly depends on genetic testing. Clinicians need to be vigilant, strengthen the early understanding of the disease, and improve the prognosis.

Sequencing Technology in Molecular Diagnosis of Spinal Muscular Atrophy Caused by SMN1 Deletion / 天津医药

Objective To investigate the feasibility of DNA sequencing analysis in molecular diagnosis for spinal muscular atrophy (SMA). Methods Two pairs of primers were utilized to amplify the region including 5 different bases in SMA-causative gene SMN1 and its homologue copy SMN2 by polymerase chain reaction (PCR). The first primer amplified a fragment 501 bp long spanning from SMN intron 6 to intron 7 targeting four different bases (g.31957, 32006, 32154 and 32269). The second primer reversely amplified a 189 bp long fragment within SMN exon 8 including one base-pair differ-ence (g.32734). PCR procedure was followed by Sanger sequencing technique to identify the 5 different bases. SMA patients caused by SMN1 homozygous deletion were distinguished from carriers or normal controls by absence of SMN1 specific bas-es in sequence chromatograms. This assay was performed in 7 SMA suspected patients and their parents. The specimens were also detected by PCR- restriction fragment length polymorphism (RFLP) method. Results It was found that 6 of 7 SMA suspected patients showed only SMN2 specific bases at the 5 different base positions among the region from intron 6 to exon 8, which meant the patient displaying only SMN2-specific nucleotide a, T, g, g and A at g.31957, 32006, 32154, 32269 and 32734, while their parents (carriers) showed a/g, T/C, g/a, g/a and A/G at the same sites. SMN1 gene was deleted in the patient, and the deletion region was inferred from intron 6 to exon 8. Because carriers had both SMN1 and SMN2 genes, they can be discriminated from the SMN1 deleted patient. One of 7 patients yield an unique sequence chromatogram of a, T, g, g and A/G, indicating that exon 8 of SMN1 was not deleted in this patient. Conclusion DNA sequencing analysis is an alter-native simple method for detecting SMA caused by homozygous deletion of SMN1. We recommend to replace the widely used PCR-RFLP method with DNA sequencing assay.

Análisis genético molecular en atrofia muscular espinal / Molecular evaluation in infantile spinal muscular atrophy

Introducción: La atrofia muscular espinal de la infancia (AMEi) es una enfermedad neurodegenerativa, causada principalmente por deleciones del gen SMN 1 en su locus 5q11.1-13.3. La severidad va desde el tipo I, que compromete la vida en edades tempranas, hasta el tipo IV. Objetivos: Se describen hallazgos moleculares en pacientes con AME, nacionalmente remitidos al Instituto de Neurología y Neurocirugía así como se reporta la frecuencia por 100.000 habitantes en cada una de las provincias de la isla. Pacientes y Métodos: 105 pacientes fueron estudiados, remitidos entre 1997 y 2011. Para la detección de las deleciones se utilizó la técnica de reacción en cadena de la polimerasa (PCR) con cebadores correspondientes a los exones 7 y 8 del gen SMN 1, y digestión con enzimas DraI y DdeI respectivamente y analizados en gel de agarosa al 2 por ciento. Resultados y Discusión: Se encontró un 59 por ciento diagnosticados como AME I, 28,6 por ciento AME II, 12,4 por ciento AME III. Del total de casos 36,2 por ciento resultaron tener deleción de los exones 7 y 8, 35,2 por ciento deleción del exón 7 solamente y 28,2 por ciento no presentaron deleción de los exones correspondientes. Se discuten dichos resultados de acuerdo a la literatura internacional. Se presentan los resultados de frecuencias por 100.000 habitantes en cada provincia del país y discuten dichas frecuencias de acuerdo a la diversidad ancestral de la población cubana. Se concluye lo novedoso del estudio que constituye el primer reporte en una población caribeña.

Introduction: Infantile Spinal Muscular Atrophy (infantile SMA) is a neurodegenerative disease caused primarily by the deletion of the SMN1 gene at 5q11.1 - 13.3. Its severity ranges from type I, in early childhood, to type IV. Objectives: To describe molecular findings in patients with SMA, who were nationally referred to the Institute of Neurology and Neurosurgery and to describe the frequency per 100,000 people in each province of the island. Patients and Methods: 105 patients, referred between 1997 and 2011, were studied. The polymerase chain reaction (PCR) technique was used to detect the deletions of exons 7 and 8 of the SMN1 gene, and DraI and DdeI enzymes, in 2 percent agarose gel, were used for digestion. Results: 59 percent of the patients were diagnosed with SMA I, 28.6 percent with SMA II and 12.4 percent with SMA III. 36.2 percent of total patients presented deletions of exons 7, 8, 35.2 percent only deletion of exon 7 and 28.2 percentdid not present deletion of exons. Conclusion: These results are discussed according to the international literature. The frequency per 100,000 inhabitants in each province is presented and discussed according to ancestral diversity of the Cuban population. Also, the originality of the study is mentioned as it is the first report of this type in a Caribbean population.

Advances in the genetics of spinal muscular atrophy in childhood / 国际儿科学杂志

Spinal muscular atrophy in childhood is one of the most common neuromuscular disorders with an autosomal recessive mode of inheritance. The main pathogenesis is homozygous loss and small intragenic mutations of the SMN1. SMN2 ,as a very identical copy of SMN1, modulates the disease severity. The functional difference between both genes is a variance of single nucleotide within the coding region, causing silent mutation obviously to decrease SMN2 transcripts. Histone deacetylase inhibitors have been shown better perspective in clinical trials.

Molecular biological diagnosis of Spinal Muscular atrophy

Spinal muscular atrophy(SMA) is the second most common fatal disease of childhood with autosomal dominant mode of inheritance, and in its less severe form the third most common neuromuscular disease of childhood after Duchenne muscular dystrophy. The genetic defect was found to be on the long arm of chromosome 5(5q11.2-q13.3) where many genes and microsatellite markers were missing. One of the most important genes is the Survival Motor Neuron(SMN) gene which is homozygously missing in 90% of SMA patients. Another important gene, the Neuronal Apoptosis Inhibitory Protein(NAIP) gene was found to be defective in 67% of SMA type I patients. Studies so far suggest SMA occurs when the genes on the long arm of chromosome 5 are mutated or deleted. Recently our hospital encountered 2 SMA patients of type I and II respectively. These patients both had homozygously defective SMN genes but intact NAIP genes. We are reporting these cases with bibliographic review and discussion. Korean SMA patients presumably have defects in SMN genes similar to those found in European patients, although the siginificance of NAIP genes remains to be established. SMN gene defects can be easily diagnosed using PCR and restriction enzymes, and this method could be applied towards convenient prenatal diagnosis and towards screening for family members at risk.