| IntroductionSCAs(spinocerebellar ataxias)is complex group of neurodegener-ativedisorders affected centeral neuroal system and peripheral neuroal system, demonstrates autosomal dominant inherity, characterizd multiple-neuropathy syndromy , cerebellar spinopontine atrophy, loss of neurons and gliosis in substantia nigra,nuclei pontis . Clinical syndromy commonly are observed late-onset ataxia, uncoordinated gait, dysarth-na, difficulties in swallowing, ophthalmoplegia, and so on.In 1993 SCA1 gene was firstly located and cloned in 6p23 , more than ten kinds of subtypes which involved in human hereditary ataxia have been disclosed, and most of them was cloned, but still 1/4 ~ 1/ 2 ataxial locuis were unknown. Study revealed that SCAs were caused almost by abnomal expansion of CAG. At same time, SCAs shows a great genetically heterogeneity and gentic multi-effected.The aim that we study the distribution of genotype of SCAs in the area of the northeastern in China is order to identify the limitation ofCAG copies in nomal and abnomal people. SCA1 and SCA3/MJD are the highest prevalence in SCAs with 10 - 30% and 10 - 50% each. We practice a new mdthod to detect CAG expansion, further more for presymptomatic diagnosis; prenatal diagnosis in clinic basing on mole-culer gentic classification.Material110 people is hanzu is in northeastern of China . 8 families with 25 patients and 6 sporadic cases involed in spinocerebellar ataxias; A sample of 1 ~5ml blood were collected by venipuncture from each individual.MethodDNA was isolated from peripheral blood. Different DNA fragments were detected by autoradiograph method , some of them measured with fluorescence-PCR technology; Homozygosity were selected for DNA sequencing.ResultsIn 25 patients of 8 families, CAG imitative expansion in one case have been found in SCA3/MJD gene, we named it as subtype of SCA3/MJD. The normal repeat range of CAG in SCA1 and SCA3/MJD gene in 110 normal people is 20 -39 repeats and 8-33 repeats. CAG repeats in SCA1 gene is concentrate in 26 and 27 repeats, is 34.09% and 20. 91% of whole alleles,heterozygosity is 84.55%. CAG repeatsin SCA3 mainly concentrate in 8 repeats, allele frequence is 39.55% of whole alleles ,heterozygosity is 78.18%.DiscussionWe detected CAG repeats in expansion in SCAj and SCA3/MJD gene using molecular genetics method basing on clinical diagnosis. We clearfied allele distribution of SCA, and SCA3/MJD gene. Investigation result showed that SCA1 and SCA3/MJD had very strong heterogeneity. Clinic variation such as difference in onset age, lasting time, severeity and affected part of body appears difference in differeat families , even in the different individuals of the same families. It is clear that classification for gene typing is only accurate method for SCAs.The high repeat of CAG trinucleotide in SCA1 and SCA3/MJD gene make the GC amount remarkable increase during PCR amplifying. So condition for PCR is very importent. Autoracliography techol-ogy has high sensitivity, especially to lower PCR product, We chosed a few of representatice specific bands and sequenced amplifying DNA then compared with other fragments . The method is cheaper and easier for clinical practice. There are great 1 for the social and the economic benefit.One pantient have been found that CAG repeats was 62 beyond nomal range in SCA3/MJD gene, we named it SCA3/MJD.The shortest repeats of ( CAG) 8 in alleles of SCA3/MJD genes may be special genotype in northeastern of china.ConclusionIn this study, we set up a new method for detecting the CAG repeats in our nation firstly, and a new genotype of SCA3/MJD was found , there are some other new subtype in SCAs. We track advanced development, systematically, scientifically summarize GAG repeats in SCA1 and SCA3/MJD gene in our northeastern area, and make statistics correctly to alleles, making hard base for studying other subtype. |
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