Subsequently, the membrane was hybridized with an end-labeled (CAGG) 5 probe. Long-range PCR fragments were subjected to agarose gel electophoresis and capillary transfer to a nylon membrane. ( b) Southern blotting of long-range PCR products of the CCTG repeat in the CNBP gene. Fluorescently-labeled PCR products of a healthy individual (top panel) and an affected individual (bottom panel) with one normal allele and one expanded allele (>100 repeats) were separated by capillary electrophoresis. ( a) Fragment-length analysis of QP-PCR products of the CCTG repeat in the CNBP gene. Molecular diagnostic tests in myotonic dystrophy type 2. Normal sized alleles and expansions are indicated. Estimation of the lengths of the repeat expansions can be done using the size markers (M). Visualized fragments were from a healthy control (1), and patients with one normal and one expanded allele (2 and 3). Subsequently, the membrane was hybridized with a P-labeled probe for the DMPK gene. Genomic DNA samples were fragmented using BglI and subjected to electophoresis and capillary blotting to a nylon membrane. ( c) Southern blotting of genomic DNA probed for the DMPK gene. Visualized repeats were from a healthy control (lane 2), a patient with a heterozygous expansion in the size range of 51–150 repeats (lane 1), and a patient with a heterozygous expansion in the size range over 150 repeats (lane 3). Subsequently, the membrane was hybridized with a labeled (CAG) 5 probe. Long-range PCR fragments were subjected to to agarose gel electophoresis and capillary transfer to a nylon membrane. ( b) Southern blotting of long-range PCR-products of the CTG repeat in the DMPK gene. Fluorescently-labeled PCR products of a healthy individual having two normal alleles (5 and 13 CTG repeats top panel) and an affected individual (bottom panel) with one normal allele (5 repeats) and one expanded allele were separated by capillary electrophoresis. ( a) Fragment-length analysis of TP-PCR products of the CTG repeat in the DMPK gene. Molecular diagnostic tests in myotonic dystrophy type 1. Here, we describe best practice guidelines for clinical molecular genetic analysis and reporting in DM1 and DM2, including presymptomatic and prenatal testing. Because of the disease characteristics in DM1 and DM2, appropriate molecular testing and reporting is very important for the optimal counseling in myotonic dystrophy. Nevertheless, these repeat sizes have limited predictive values on individual bases. The length of the (CTG)n repeat expansion in DM1 correlates with disease severity and age of onset. Both DM1 and DM2 are caused by unstable DNA repeats in untranslated regions of different genes: A (CTG)n repeat in the 3'-UTR of the DMPK gene and a (CCTG)n repeat in intron 1 of the CNBP (formerly ZNF9) gene, respectively. In myotonic dystrophy type 2 (DM2), no anticipation is described, but cardiac conduction abnormalities as in DM1 are observed and patients with DM2 additionally have muscle pain and stiffness. In subsequent generations, the symptoms in DM1 may present at an earlier age and have a more severe course (anticipation). In adult patients, cardiac conduction abnormalities may occur and cause a shorter life span. The symptoms and severity of myotonic dystrophy type l (DM1) ranges from severe and congenital forms, which frequently result in death because of respiratory deficiency, through to late-onset baldness and cataract. Myotonic dystrophy is an autosomal dominant, multisystem disorder that is characterized by myotonic myopathy.
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