Identification of two survival motor neuron gene 1 gene mutations and evaluation of their effects on fulllength survival motor neuron gene 1 transcripts

Abstract

Objective To perform mutation analysis of survival motor neuron gene 1 (SMN1) in two spinal muscular atrophy (SMA) patients and their parents to evaluate the effects of the two SMN1 gene mutations on the transcript levels of the gene and preliminarily predict their effects on the structure and function of SMN protein. Methods Mutation analysis of SMN1 gene was carried out by multiplex ligation-dependent probe amplification，reverse transcript-polymerase chain reaction (RTPCR) and cloning sequencing.Transmission of the mutations was confirmed by the mutation analysis in patients’parents.The full-length SMN1 (SMN1-fl) transcript levels of the patients carrying these subtle mutations were detected using quantitative RT-PCR. Results The two patients were diagnosed as SMA Ⅱ and SMA Ⅲ. They carried p.Val19GlyfsX21 and p.Ala2Gly SMN1 mutations in SMN1 gene，respectively.Both of the two mutations were originated from their fathers.Compared with the healthy individuals (23.5±4.9)，the two patients had a significant reduction in the level of SMN1-fl transcripts (t=3.322，P=0.011 (p.Ala2Gly);t=6.964，P=0.000 (p.Val19Glyfs X21)). However，compared with the healthy carriers (14.1±4.5)，the patient with p.Ala2Gly mutation had no significant reduction in the level of SMN1-fl transcripts (13.9±3.6，t=0.058，P=0.955); however，the patient with p.Val19GlyfsX21 mutation had a significant reduction (4.9±2.4，t=3.725，P=0.004). Conclusions Two SMN1 gene mutations are identified in our study.The mutation p.Val19GlyfsX21 is a novel mutation and p.Ala2Gly is firstly reported in Chinese SMA patients. p.Val19GlyfsX21 may possibly lead to decreased SMN1-fl mRNA by nonsense-mediated messenger RNA decay，however，p.Ala2Gly has no obvious effects on the amount of the SMN1-fl transcripts，indicating that its deleterious effect may be occurring at SMN protein level or the function of SMN protein. Key words: Muscular atrophy，spinal; Survival of motor neuron 1 protein; Point mutation; Gene dosage; Nucleic acid amplification techniques