Abnormal myotonic dystrophy protein kinase levels produce only mild myopathy in mice (original) (raw)
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Human Molecular Genetics, 1998
There is a good correlation between repeat size (at least in leucocytes), clinical severity and age of onset. The trinucleotide repeat instability mechanisms involved in DM and other human genetic diseases are unknown. We studied somatic instability by measuring the CTG repeat length at several ages in various tissues of transgenic mice carrying a (CTG) 55 expansion surrounded by 45 kb of the human DM region, using small-pool PCR. These mice have been shown to reproduce the intergenerational and somatic instability of the 55 CTG repeat suggesting that surrounding sequences and the chromatin environment are involved in instability mechanisms. As observed in some of the tissues of DM patients, there is a tendency for repeat length and somatic mosaicism to increase with the age of the mouse. Furthermore, we observed no correlation between the somatic mutation rate and tissue proliferation capacity. The somatic mutation rates in different tissues were also not correlated to the relative inter-tissue difference in transcriptional levels of the three genes (DMAHP, DMPK and 59) surrounding the repeat.
Genomics, 1996
nisms involved in the regulation of the somatic stability of the (CTG) n repeats in DM. ᭧ 1996 Academic Press, Inc. The mutation associated with myotonic dystrophy (DM) is the expansion of an unstable trinucleotide repeat, (CTG) n , in the 3-untranslated region of the myo-INTRODUCTION tonin protein kinase gene. Although expanded repeats show both germline and somatic instability, the mech-An expansion of an unstable (CTG) n repeat [p(AGC) n anisms of the instability are poorly understood. To esby HGM 10.5 nomenclature] in the 3-untranslated retablish a model system in which somatic instability gion of the myotonin protein kinase (Mt-PK) gene of the DM repeat could be studied in more detail, we (DMPK by GDB nomenclature) is associated with myoestablished lymphoblastoid cell lines (LBCL) from DM tonic dystrophy (DM) (Fu et al., 1992; Mahadevan et patients. Analysis of the DNA from DM LBCL using Brook et al., 1992). In addition to frequently Southern blotting showed that the (CTG) n repeats observed intergenerational repeat size differences, sowere apparently stable up to 29 passages in culture.
Mitotic drive' of expanded CTG repeats in myotonic dystrophy type 1 (DM1)
Human Molecular Genetics, 2001
In myotonic dystrophy type 1 (DM1), an expanded CTG repeat shows repeat size instability in somatic and germ line tissues with a strong bias toward further expansion. To investigate the mechanism of this expansion bias, 29 DM1 and six normal lymphoblastoid cell lines (LBCLs) were single-cell cloned from blood cells of 18 DM1 patients and six normal subjects. In all 29 cell lines, the expanded CTG repeat alleles gradually shifted toward further expansion by 'step-wise' mutations. Of these 29 cell lines, eight yielded a rapidly proliferating mutant with a gain of large repeat size that became the major allele population, eventually replacing the progenitor allele population. By mixing cell lines with different repeat expansions, we found that cells with larger CTG repeat expansion had a growth advantage over those with smaller expansions in culture. This growth advantage was attributable to increased cell proliferation mediated by Erk1,2 activation, which is negatively regulated by p21 WAF1 . This phenomenon, which we designated 'mitotic drive', is a novel mechanism which can explain the expansion bias of DM1 CTG repeat instability at the tissue level, on a basis independent of the DNA-based expansion models. The lifespans of the DM1 LBCLs were significantly shorter than normal cell lines. Thus, we propose a hypothesis that DM1 LBCLs drive themselves to extinction through a process related to increased proliferation.
Neurological Sciences, 2005
Myotonic dystrophy type 1 (DM1) is an autosomal dominant disease caused by a trinucleotide repeatexpansion, cytosine-thymine-guanine (CTG)n, in the 3 ı untranslated region of a gene encoding the myotonic dystrophy protein kinase (DMPK). To correlate CTG expansion and protein expression, we studied muscle specimens from 16 adult DM1 patients using three anti-DMPK antibodies for immunoblotting. We estimated the amount of the full-length DMPK (85 kDa) in muscle biopsies from normal controls and from DM1 patients carrying different (CTG) n expansions. We found that DMPK concentration was decreased to about 50% in DM patients' muscles; the protein decrease did not seem correlated with the CTG repeat length. However, the fibre type composition in skeletal muscle seemed somehow to affect DMPK decrease, as the lowest level of the enzyme was found in patients with the lowest content of type 1 fibre.
Myotonic dystrophy with no trinucleotide repeat expansion
Annals of Neurology, 1994
We report 3 patients from 2 families with myotonic dystrophy who d o not show an abnormal expansion of CTG trinucleotide repeats within the myotonic dystrophy gene. Characteristic features of myotonic dystrophy in these patients were frontal balding, cataracts, cardiac conduction abnormalities, and testicular atrophy with rnyotonia and muscle weakness. Results of muscle histopathology were consistent with myotonic dystrophy. Genetic analysis of leukocyte and muscle DNA showed a normal number of CTG repeats. The demonstration of normal CTG repeat number for the myotonic dystrophy gene does not exclude the diagnosis of myotonic dystrophy. Thornton CA, Griggs RC, Moxley RT 111. Myotonic dystrophy with no trinucleotide repeat expansion. Ann Neurol 1994;35:269-272 Expansion of (CTG). trinucleotide repeats in the 3' untranslated region of a putative protein kinase gene is found in 98 t o 100% of patients with myotonic dystrophy (DM) [l-4). Detailed information about individuals who carry the diagnosis of DM but who do not have (CTG). repeat expansion is unavailable C3, 5-71 or casts doubt on t h e diagnosis {?, 81. We report clinical findings, muscle pathology, and genetic data on 3 individuals from 2 families with D M . No trinucleotide repeat expansion has been detected in these patients.
The American Journal of Human Genetics, 2004
The CTG repeat at the 3 untranslated region of the dystrophia myotonica protein kinase (DMPK) gene shows marked intergenerational and somatic instability in patients with myotonic dystrophy (DM1), when the repeat is expanded to more than ∼55 repeats. Intensive research has yielded some insights into the timing and mechanism of these intergenerational changes: (1) increases in expansion sizes occur during gametogenesis but probably not during meiosis, (2) the marked somatic mosaicism becomes apparent from the 2nd trimester of development onward and increases during adult life, and (3) DNA repair mechanisms are involved. We have performed preimplantation genetic diagnosis for DM1 since 1995, which has given us the unique opportunity to study the expanded CTG repeat in affected embryos and in gametes from affected patients. We were able to demonstrate significant increases in the number of repeats in embryos from female patients with DM1 and in their immature and mature oocytes, whereas, in spermatozoa and embryos from male patients with DM1, smaller increases were detected. These data are in concordance with data on other tissues from adults and fetuses and fill a gap in our knowledge of the behavior of CTG triplet expansions in DM1.
Molecular Biology Reports, 2011
Myotonic dystrophy type 1 (DM1), the most common form of adult muscular dystrophy, is caused by anormal expansion of CTG trinucleotide repeats located in the 3 0 -untranslated region of the DMPK gene. The clinical features of DM1 are multisystemic and highly variable, and the unstable nature of CTG expansion causes wide genotypic and phenotypic presentations. In this study, we described to our knowledge for the first time the molecular diagnosis of myotonic dystrophy type 1 patients in the Mexican population, applying a fluorescent PCR method in combination with capillary electrophoresis analysis of the amplified products. We identified expanded alleles in 45 out of 50 patients (90%) with clinical features of myotonic disease. Furthermore, genotyping of 400 healthy subjects revealed the presence of 25 different alleles, ranging in size from 5 to 34 repeats. The most frequent allele was 13 CTG repeats (38.87%) and the frequency for alleles over 18 CTG repeats was 6.7%. Molecular test is essential for DM1 diagnosis and distribution of the CTG repeat alleles present in the Mexican population are significantly different from those of other populations.
Human Molecular Genetics, 2012
Deciphering the contribution of genetic instability in somatic cells is critical to our understanding of many human disorders. Myotonic dystrophy type 1 (DM1) is one such disorder that is caused by the expansion of a CTG repeat that shows extremely high levels of somatic instability. This somatic instability has compromised attempts to measure intergenerational repeat dynamics and infer genotype-phenotype relationships. Using single-molecule PCR, we have characterized more than 17 000 de novo somatic mutations from a large cohort of DM1 patients. These data reveal that the estimated progenitor allele length is the major modifier of age of onset. We find no evidence for a threshold above which repeat length does not contribute toward age at onset, suggesting pathogenesis is not constrained to a simple molecular switch such as nuclear retention of the DMPK transcript or haploinsufficiency for DMPK and/or SIX5. Importantly, we also show that age at onset is further modified by the level of somatic instability; patients in whom the repeat expands more rapidly, develop the symptoms earlier. These data establish a primary role for somatic instability in DM1 severity, further highlighting it as a therapeutic target. In addition, we show that the level of instability is highly heritable, implying a role for individual-specific transacting genetic modifiers. Identifying these transacting genetic modifiers will facilitate the formulation of novel therapies that curtail the accumulation of somatic expansions and may provide clues to the role these factors play in the development of cancer, aging and inherited disease in the general population.
Human Molecular Genetics, 2000
observed through successive generations and the size of the repeat is generally correlated with the severity of the disease and with age at onset. Furthermore, tissues from DM patients exhibit somatic mosaicism that increases with age. We generated transgenic mice carrying large human genomic sequences with 20, 55 or >300 CTG, cloned from patients from the same affected DM family. Using large human flanking sequences and a large amplification, we demonstrate that the intergenerational CTG repeat instability is reproduced in mice, with a strong bias towards expansions and with the same sex-and size-dependent characteristics as in humans. Moreover, a high level of instability, increasing with age, can be observed in tissues and in sperm. Although we did not observe dramatic expansions (or 'big jumps' over several hundred CTG repeats) as in congenital forms of DM, our model carrying >300 CTG is the first to show instability so close to the human DM situation. Our three models carrying different sizes of CTG repeat provide insight on the different factors modulating the CTG repeat instability.