Real-Time Based Detection of SMN1 Deletion Among Egyptian Carriers of SMA: A Pilot Study

Proximal spinal muscular atrophy (SMA) is one of the most common autosomal recessive diseases, where it has an estimated incidence of 1 in 6000-10000 live births and a carrier frequency of 1 in 40-60. SMA patients are classified into three clinical types based on age of onset and severity of symptoms. Mutations in the survival motor neuron gene 1 (SMN1) are determinant for development of the disease, whereas the number of copies of SMN2 gene plays a role as a phenotypic modifier factor. Approximately 94% of patients have homozygous absence of the SMN1 whereas most carriers have only one SMN1 gene copy, this study aimed to establish SMA carrier detection test through SMN1 quantitative analyses using real-time PCR technique. The study included ten obligate heterozygotes, three patients with homozygous deletion of SMN1 and ten normal controls. Genomic DNA was extracted from peripheral blood samples. Real-time PCR for SMN1 gene was optimized and related to that of albumin as a reference gene. The copy number of SMN1 gene was determined by comparative thresh- old cycle (Ct) method. The homozygous SMN1 deletion ratio of patients was 0.00, the hemizygous SMN1 deletion ratio of carriers ranged from 0.39-0.59 and about 0.84-2.19 in normal controls. This pilot study provided accurate and reliable test for SMA carrier detection, genetic counseling and prenatal diag- nosis.