Determination of Type 7 (SCA7) and Type 17 (SCA17) CAG trinucleotide repeats in patients with Spinocerebellar Ataxia syndrome

Spinocerebellar Ataxia (SCA) is a progressive, degenerative, genetic disease with multiple types determined until now. It is characterized by the progressive function disorder in cerebellum, brainstem and spinal cord. Clinical symptoms are generally incoordination of gait, poor coordination of hands and feet, distortion of speech, loss of vision and dementia. Mostly atrophy of the cerebellum is seen in patients however, it is known that different ataxias affect different regions of the cerebellum. Today, more than 30 different types of hereditary SCA is determined according to different chromosomal locus or different gene. Different types of ataxias have very similar clinical symptoms however, they are caused by different gene locus and mutations in these locus are also different. Due to this reason clinical diagnosis of the disease is very hard but mutations in the specific locus can be determined by molecular methods and disease can be diagnosed. The mutations causing SCA are usually the abnormal increases in trinucleotide repeats (TNR). SCA7 is caused by the increased repeats in ATXN7 gene which is located on p21.1 region of 3rd chromosome and SCA17 is caused by the increased repeats in TATA box-binding protein (TBP) gene which is located on q27 region of 6th chromosome.In this research, blood samples are collected from patients who applied to Neurology and Pediatric Neurology clinics of Çukurova University Medical School and are diagnosed for SCA and from healthy people for control. The repeat numbers of the SCA7 and SCA17 regions of the patients and normal people are determined by the PCR amplification of the regions that show expansion followed by agarose gel electrophoresis to compare these PCR products with the known DNA fragments.In our research; during SCA7 screening 1 person (1/60, 1,7%) is identified as having full penetrance, during SCA17 screening 3 people (3/159, 1,9%) are identified as having low penetrance with 43-48 TNR numbers, 3 people (3/159, 1,9%) are identified as having full penetrance with 49-66 TNR numbers and all having heterozygous genotype is determined. Prevalences of the SCA7 and SCA17, averages and frequencies of the repeat numbers are determined. Furthermore, relation of the repeat numbers and disease onset age is examined.