@#BACKGROUND. Spinal muscular atrophy (SMA MIM#253300) is a heterogeneous group of neuromuscular disorders caused by degeneration of anterior horn cells. Spinal muscular atrophy is the second most common autosomal recessive disorder. The first substantive descriptions of SMA occurred at the end of the 19th century when Werdnig and Hoffman characterized the features of autosomal recessive SMA. SMA is broadly classified into four major categories characterized by the age of onset as well as severity of the disease. Clinically proximal weakness, predominantly athropy, upper muscle athropy and other muscle weakness including of facial, scapula and respiratory were reported. SMA is inherited by X chromosomal, autosomal recessive and dominant mode. In our study, we recruited an individual diagnosed with SMA, without SMN1 gene mutation to investigate BICD2 mutation. Peripherial blood from the patient and his family members were taken to extract genomic DNA according to commercial protocol. Amplification of target gene was done by special primers. DNA sequencing was done to detect a mutation. As a result, we identified a mutation in location c.484 C>T of third exon of BICD2 gene. This mutation is was a heterozygous in mother’ and child’ DNA, SIFT and Polyphen program was used to detect its pathogenic effect. We also checked by Grantham matrix score is 180.0 representing it,s changing acid and alkaline feature in this amino acid. We diagnoses a suspected case with SMA by his clinical symptoms as a SMA type III, Kugelberg-Belander desease. We detected a mutation of BICD2 gene in a patient with SMA. This mutation altered acid and alkaline checked by Grantham matrix. This mutation has never reported before, showing 100% pathogenic effect on protein function, but because of highly penetrate feature of this disease makes its inheritance mode of autosomal dominant pattern.