Combination of SMN2 copy number and NAIP deletion predicts disease severity in spinal muscular atrophy.
Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by mutations in the SMN1 gene. The SMN2 gene is highly homologous to SMN1 and has been reported to be correlated with severity of the disease. The clinical presentation of SMA varies from severe to mild, with three clinical subtypes (type I, type II, and type III) that are assigned according to age of onset and severity of the disease. Here, we aim to investigate the potential association between the number of copies of SMN2 and the deletion in the NAIP gene with the clinical severity of SMA in patients of Malaysian origin. Forty-two SMA patients (14 of type I, 20 type II, and 8 type III) carrying deletions of the SMN1 gene were enrolled in this study. SMN2 copy number was determined by fluorescence-based quantitative polymerase chain reaction assay. Twenty-nine percent of type I patients carried one copy of SMN2, while the remaining 71% carried two copies. Among the type II and type III SMA patients, 29% of cases carried two copies of the gene, while 71% carried three or four copies of SMN2. Deletion analysis of NAIP showed that 50% of type I SMA patients had a homozygous deletion of exon 5 of this gene and that only 10% of type II SMA cases carried a homozygous deletion, while all type III patients carried intact copies of the NAIP gene. We conclude that there exists a close relationship between SMN2 copy number and SMA disease severity, suggesting that the determination of SMN2 copy number may be a good predictor of SMA disease type. Furthermore, NAIP gene deletion was found to be associated with SMA severity. In conclusion, combining the analysis of deletion of NAIP with the assessment of SMN2 copy number increases the value of this tool in predicting the severity of SMA.
Watihayati
Mohd Shamshudin
MS
Human Genome Center, School of Medical Sciences, Health Campus, Universiti Sains Malaysia, 16150 Kubang Kerian, Kota Bharu, Kelantan, Malaysia.
Fatemeh
Hayati
H
Marini
Marzuki
M
Atif
Amin Baig
AB
Zahiruddin
Wan Mohd
WM
Sasongko
Teguh Haryo
TH
Tang
Thean Hock
TH
Zabidi-Hussin
Z A M H
ZA
Nishio
Hisahide
H
Zilfalil
Bin Alwi
BA
D004252:DNA Mutational Analysis / Q000379:methods; D005091:Exons; D017353:Gene Deletion; D018628:Gene Dosage; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D009134:Muscular Atrophy, Spinal / Q000145:classification / Q000175:diagnosis / Q000235:genetics*; D009154:Mutation; D051616:Neuronal Apoptosis-Inhibitory Protein / Q000235:genetics*; D016133:Polymerase Chain Reaction / Q000379:methods; D011237:Predictive Value of Tests; D011379:Prognosis; D055532:SMN Complex Proteins / Q000235:genetics*; D012720:Severity of Illness Index; D055540:Survival of Motor Neuron 2 Protein
D051616:Neuronal Apoptosis-Inhibitory Protein; D055532:SMN Complex Proteins; C526477:SMN2 protein, human; D055540:Survival of Motor Neuron 2 Protein