Clinical And Molecular Studies On Myotonic Dystrophy

Objectives1. To summarize the clinical and pathological features of myotonic dystrophy and further the diagnosis of this disease.2. To determine the distributional characteristics of CTG trinucleotide repeat and CCTG tetranucleotide repeat in healthy individuals from Chinese Han nationality.3. To study the gene diagnosis of myotonic dystrophy.Methods1. The clinical and pathological characteristics of 24 DM cases were analyzed retrospectively.2. Polymerase chain reaction, denaturing polyacrylamide gel electrophoresis, silver staining and sequencing were used to find the distribution of CTG repeat and CCTG repeat in 145 normal subjects.3. Polymerase chain reaction and sequencing were applied to identify the genetic diagnosis of 24 DM patients and their family members.Results1. The clinical and pathological features of DM1 were as follows: Firstly, the disease always occurred during young adulthood and progressed slowly. Secondly, DM1 patients usually owned positive family history. Thirdly, DM1 was characterized by myotonia, weakness and atrophy in multigroup muscles, especially in distal limbs, neck and face. Fourthly, DM1 was a multisystem disorder. Premature balding in male patients was an important clinical feature. Fifthly, spontaneous myotonic discharges and myogenic damages were shown on electromyogram.Sixthly, increased number of central nuclei, nuclear chains and predominant atrophic typeⅠfibers were found in muscle biopsy.2. The copies of CTG repeat located in the DMPK gene varied in different individuals. We found 19 kinds of the CTG repeat fragments from 290 chromosomes, in which the frequency of 5 copies fragment was the highest (37.9%). That of four kinds in the range of 10 to 13 repeats were high, 11 repeats was 19.0%, 13 repeats was 13.1%, 12 repeats was 7.6% and 10 repeats was 6.2% respectively. The rest kinds were rare and that of more than 23 copies had not been found. Heterozygote frequency in this group was 75.9%.3. The size of (TG)n(TCTG)n(CCTG)n repeat located in the ZNF9 gene was variable. 28 kinds of fragments were found from 290 chromosomes totally, in which the percentage of 134bp fragment was the highest (14.1%). That of six kinds were high, 126bp fragment was 10.0%, 128bp fragment was 9.3%,124bp fragment was 8.6%, 138bp fragment was 6.6%, 140bp fragment was 6.2% and 130bp fragment was 5.2% respectively. The rest kinds were rare and that of larger than 160bp had not been found. Heterozygote frequency in this population was 91.0%.4. After amplification, the products of CTG repeat were separated by electrophoresis in agarose gel or denaturing polyacrylamide gel. Only one band of 5-14 CTG repeats was found in 24 DM patients. The amplification products of 3 patients′ fathers in gel showed two bands, one of them was abnormal with 53, 70 or 74 repeats confirmed by sequencing respectively. That of the rest family members (17) showed two normal bands with 5-16 CTG repeats. The amplification products of (TG)n(TCTG)n(CCTG)n repeat were separated by electrophoresis in denaturing polyacrylamide gel. All DM patients (24) and their family members (20) were heterozygote except one homozygote.Conclusions1. Though clinical manifestation of DM1 was various, the disease had remarkable clinical and pathological characteristics.2. The lengths of CTG repeat and (TG)n(TCTG)n(CCTG)n repeat tract in the Hanswere of racial specificity and high polymorphism.3. All 24 patients were identified to be myotonic dystrophy type 1 but not myotonic dystrophy type 2 by molecular methods. Only the normal size and small expansions of CTG repeat could be amplified by PCR. The larger expansions should be detected through Southern blot.