Deletions in the survival motor neuron gene in Iranian patients with spinal muscular atrophy.
BACKGROUND
Spinal muscular atrophy (SMA) is a common neuromuscular disorder with progressive paralysis caused by the loss of alpha-motor neurons in the spinal cord. The survival motor neuron (SMN) protein is encoded by 2 genes, SMN1 and SMN2. The most frequent mutation is the biallelic deletion of exon 7 of the SMN1 gene. In SMA, SMN2 cannot compensate for the loss of SMN1, due to the exclusion of exon 7. The aim of our study was to estimate the frequency of the common SMN1 exon 7 deletion in patients referred to our centre for carrier detection and prenatal diagnosis.


METHODS
We performed the detection of exon 7 deletion of the SMN1 gene for the affected patients and fetuses suspected to have SMA.


RESULTS
Of 243 families, 195 were classified as SMA type I, 30 as type II, and 18 as type III according to their family histories. The analysis of exon 7 deletion among living affected children showed that 94% of the patients with SMA type I, 95% with type II families and 100% with type III had homozygous deletions. Of the prenatal diagnoses, 21 (22.8%) of the 92 fetuses were found to be affected and these pregnancies were terminated.


CONCLUSIONS
The homozygosity frequency for the deletion of SMN1 exon 7 for all 3 types was (94%), similar to those of Western Europe, China, Japan and Kuwait.
Hasanzad
Mandana
M
Kariminejad-Najmabadi Pathology & Genetics Center, 14665/154 Tehran, Iran.
Golkar
Zahra
Z
Kariminejad
Roxana
R
Hadavi
Valeh
V
Almadani
Navid
N
Afroozan
Fariba
F
Salahshurifar
Iman
I
Shafeghati
Yousef
Y
Kahrizi
Kimia
K
Najmabadi
Hossein
H
D004247:DNA / Q000235:genetics*; D005091:Exons; D005260:Female; D017353:Gene Deletion; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease; D006801:Humans; D007492:Iran / Q000453:epidemiology; D008297:Male; D009134:Muscular Atrophy, Spinal / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods; D015995:Prevalence; D011379:Prognosis; D012189:Retrospective Studies; D055532:SMN Complex Proteins / Q000235:genetics*; D055533:Survival of Motor Neuron 1 Protein / Q000235:genetics*; D055540:Survival of Motor Neuron 2 Protein
D055532:SMN Complex Proteins; C526471:SMN1 protein, human; C526477:SMN2 protein, human; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein; D004247:DNA