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Results for “DNA Repeat Expansion”

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PubMed2006

Intergeneration CAG expansion and contraction in a Chinese HD family.

The prevalence of juvenile-onset Huntington's disease (HD) is about ten times lower than adult HD. Here we report a Chinese HD family showing both intergeneration CAG expansion and contraction. The expansion resulted from a paternal transmission which leads to juvenile-onset HD for a 17-year-old Chinese boy (III-5). More interestingly, a contraction was noticed in a maternal transmission (III-3), which changed the CAG repeat from an expanded, disease-causing allele (48 repeats) to a normal or intermediate allele (34 repeats). Of note, the contraction resulted in a deletion of 14 CAG repeats, which is much larger than previously reported contractions. Our results are consistent with previous observations in Western Caucasians that juvenile-onset HD is more likely inherited through the male germline.

Adolescent↗

PubMed2000

Correlations between individual clinical manifestations and CTG repeat amplification in myotonic dystrophy.

Myotonic dystrophy (DM) is a multisystemic disease caused by the expansion of a CTG repeat, located in the 3'-untranslated region of the DMPK gene. The number of CTG repeats broadly correlates with the overall severity of the disease. However, correlations between CTG repeat number and presence/absence or severity of individual clinical manifestations in the same patients are yet scarce. In this study the number of CTG repeats detected in blood cells of 24 DM subjects was correlated with the severity of single clinical manifestations. The presence/absence of muscular atrophy, respiratory insufficiency, cardiac abnormalities, diabetes, cataract, sleep disorders, sterility or hypogonadism is not related to the number of CTG repeats. Muscular atrophy and respiratory insufficiency are present with the highest frequency, occurring in 96 and 92% of the cases, respectively. A significant correlation was found with age of onset (r = -0.57, p<0.01), muscular disability (r = 0.46, p<0.05), intellective quotient (r = -0.58, p<0.01) and short-term memory (r= -0.59, p<0.01). Therefore, the CTG repeat number has a predictive value only in the case of some clinical manifestations, this suggesting that pathogenetic mechanisms of DM may differ depending on the tissue.

Adolescent↗

PubMed2004

New clues on the origin of the Friedreich ataxia expanded alleles from the analysis of new polymorphisms closely linked to the mutation.

Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disorder commonly caused by large expansions of a GAA repeat in the first intron of the frataxin gene, FRDA. The expansion of the triplet repeat is localized within an Alu sequence. FRDA GAA-repeat alleles can be divided into three classes depending on their lengths: short normal alleles (SN), long normal alleles (LN) and expanded pathological alleles (E). We made an accurate analysis of the Alu sequence containing the GAA repeat. We found a new single-nucleotide polymorphism (SNP) that is the closest one to the GAA repeat. We studied this new SNP and the polymorphic polyA region contiguous to the GAA triplets in two populations with different frequencies of FRDA. We found that, while both E and LN alleles seem to be genetically homogeneous and likely related, SN represents a more heterogeneous class of alleles. Indeed, one SNP variation (T) was more frequently associated with (GAA)(8) alleles, whereas the other one (C) with (GAA)(9) repeat(s). The long normal and expanded alleles presented the C haplotype. The same correlation was described for polyA-tract polymorphisms. Thus, 14A was commonly associated with (GAA)(8) alleles and 17A with (GAA)(9) alleles. The long normal alleles more frequently showed the 17A haplotype. Our data seem to suggest that all the E alleles come from LN alleles, while LN alleles come from a defined subclass of SN alleles.

Alleles↗

PubMed2002

Triplet repeat DNA structures and human genetic disease: dynamic mutations from dynamic DNA.

Fourteen genetic neurodegenerative diseases and three fragile sites have been associated with the expansion of (CTG)n (CAG)n, (CGG)n (CCG)n, or (GAA)n (TTC)n repeat tracts. Different models have been proposed for the expansion of triplet repeats, most of which presume the formation of alternative DNA structures in repeat tracts. One of the most likely structures, slipped strand DNA, may stably and reproducibly form within triplet repeat sequences. The propensity to form slipped strand DNA is proportional to the length and homogeneity of the repeat tract. The remarkable stability of slipped strand DNA may, in part, be due to loop-loop interactions facilitated by the sequence complementarity of the loops and the dynamic structure of three-way junctions formed at the loop-outs.

DNA↗

PubMed2000

Somatic frameshift alterations in mononucleotide repeat-containing genes in different tumor types from an HNPCC family with germline MSH2 mutation.

Hereditary nonpolyposis colorectal cancer (HNPCC) is caused by a germline mutation in one of several DNA repair genes, which in the tumors is reflected as microsatellite instability (MSI). MSI+ tumors have been found to carry somatic frameshift mutations in mononucleotide repeats within the coding regions of several genes involved in growth control, apoptosis, and DNA repair, e.g., TGFBRII, BAX, IGFIIR, TCF4, MSH3, and MSH6. We have studied the occurrence of somatic frameshift alterations in these mononucleotide repeat-containing genes in 24 tumors (15 colorectal cancers, 1 colon adenoma, 4 endometrial cancers, 1 ovarian cancer, 1 gastric cancer, 1 urothelial cancer, and 1 duodenal cancer) from 14 individuals in an HNPCC family with germline hMSH2 mutation. Such somatic frameshift mutations occurred at a variable frequency; the long mononucleotide repeats that characterize intronic MSI markers were mutated in the majority of tumors, 13 of the tumors displayed alterations in the (A)(10) tract of TGFBII, eight tumors (all of gastrointestinal origin) had alterations in the (A)(9) repeat of TCF4, and one to five tumors had somatic frameshift alterations in the shorter mononucleotide repeats of IGFIIR, BAX, MSH3, and MSH6. Thus, longer mononucleotide repeats were more frequently affected by somatic frameshift mutations. The pattern of alterations varied between the tumors from different family members as well as between different tumors from the same individual. To what extent this variable pattern depends on the widespread mismatch repair deficiency induced by the underlying MSH2 mutation, or represents alternative ways whereby the tumors can achieve a tumorigenic phenotype, is unknown. We suggest, however, that the accumulation of somatic frameshifts, rather than the specific loci in which these occur, drives the development of the tumorigenic phenotype in HNPCC.

Aged↗

PubMed2006

Alleles with short CAG and GGN repeats in the androgen receptor gene are associated with benign endometrial cancer.

The human androgen receptor (AR) gene possesses 2 trinucleotide repeats of CAG and GGN in exon 1. The CAG repeat corresponds to a polyglutamine tract in the N-terminal region of the receptor, that affects its transcriptional efficiency. The GGN repeat codifies for a polyglycine tract, and affects the amount of the AR protein transcribed. The endometrium contains ARs and the androgens have antiproliferative properties in cultured endometrial cancer (EC) cells. Larger CAG repeats of the AR gene give rise to a weaker transcriptional activity and have been found to be associated with endometrial carcinogenesis. The possible involvement of CAG and GGN tracts in the progression of EC is unknown. To study that possibility, we have genotyped both CAG and GGN polymorphisms of the AR gene in tumor tissue genomic DNA from a series of 204 consecutive patients with EC, and analyzed the results with regard to the pathological features and clinical outcome of patients. We classified the alleles as S (short median). The genotype with both S-CAG repeat alleles (SS-CAG) was more common in patients diagnosed at an early stage (41.6% SS-CAG vs 22.6% SL- and LL-CAG together, p = 0.048) and in tumors that did not invade the vascular space (43.0% SS-CAG vs 26.4% SL- and LL-CAG together, p = 0.034). The genotype with SS-GGN alleles was more common in well-differentiated tumors (41.2% SS-GGN vs 25.2% LS- and LL-GGN together, p = 0.017) and in endometrioid histological subtype tumors (35.3% SS-GGN vs 13.0% SL- and LL-GGN together, p = 0.034). When the genotypes of both repeats coexisting in each tumor specimen were taken into consideration, the relationship between the SS-CAG genotype and early stage remained only in the presence of the SS-GGN genotype (43.9% vs 0%, p = 0.01). No other associations were observed. In univariate survival analysis, patients with short alleles of both repeats (SS-CAG and SS-GGN genotypes simultaneously) had a lower risk of cancer-specific death (p = 0.032, mean follow-up: 63 months). Our data suggests that short CAG or GGN repeats of the AR gene are associated with a more benign condition of traditional prognostic variables in EC.

Adult↗

PubMed2005

Androgen receptor CAG and GGC polymorphisms in Mediterraneans: repeat dynamics and population relationships.

Microsatellite variation (CAG and GGC repeats) of the androgen receptor (AR) gene shows remarkable differences among African and non-African populations. In vitro studies have demonstrated an inverse relationship between the length of both microsatellites and AR activity. This fact may explain the observed association of the AR gene with prostate cancer and the strong ethnic differences in the incidence of this cancer. CAG and GGC genetic variation has been tested in a large set of populations from the Ivory Coast as well as 12 Mediterranean samples whose variation is described for the first time. The pattern of frequencies observed in the Ivory Coast agrees with data previously reported for other Sub-Saharan populations. Concerning the Mediterranean variation, Sardinian samples are characterised by low genetic diversities, and Egyptian Siwa Berbers by a particular pattern of GGC frequencies. High and Middle Atlas Moroccan Berbers are the most closely related to the Sub-Saharan variation. For both the CAG and GGC repeats, the Ivory Coast and some Moroccan samples exhibit high frequencies of low size alleles (CAG under 18 repeats, and GGC under 15 repeats) that have been associated with prostate cancer.

Analysis of Variance↗

PubMed2000

Analysis of CAG and CCG repeats in Huntingtin gene among HD patients and normal populations of India.

We have analysed the distribution of CAG and adjacent polymorphic CCG repeats in the Huntingtin gene in 28 clinically diagnosed unrelated Huntington's disease (HD) patients and in normal individuals belonging to different ethnic groups of India. The range of expanded CAG repeats in HD patients varied from 41 to 56 repeats, whereas in normal individuals this number varied between 11 and 31 repeats. We identified six CCG alleles from a total of 380 normal chromosomes that were pooled across different ethnic populations of India. There were two predominant alleles: (CCG)7 (72.6%) and (CCG)10 (20%). We report here for the first time one four-repeat CCG allele which has not been found in any population so far. We found 30 haplotypes (two loci CAG-CCG) for 380 normal chromosomes. In the present study, no statistically significant preponderance of expanded HD alleles was found on either (CCG)7 or (CCG)10 backgrounds. Our studies suggest that the overall prevalence of HD in Indian populations may not be as high as in Western populations. Further studies are necessary to identify the origin of HD mutation in these populations.

Adolescent↗

PubMed2005

Ribosomal frameshifting on MJD-1 transcripts with long CAG tracts.

The expanded CAG tract diseases are a heterogeneous group of late-onset neurodegenerative disorders characterized by the accumulation of insoluble protein material and premature neuronal cell death. Recent work has provided support for several mechanisms that may account for neurodegeneration, but no unifying mechanism has emerged. We have previously demonstrated that in SCA3, the expanded CAG tract in the MJD-1 transcript is prone to frameshifting, which may lead to the production of polyalanine-containing proteins. To further examine the occurrence of frameshifting and understand its mechanism and possible role in pathogenesis, a cellular model was established. We show that this phenomenon results from ribosomal slippage to the -1 frame exclusively, that ribosomal frameshifting depends on the presence of long CAG tracts and that polyalanine-frameshifted proteins may enhance polyglutamine-associated toxicity, possibly contributing to pathogenesis. Finally, we present evidence that anisomycin, a ribosome-interacting drug that reduces -1 frameshifting, also reduces toxicity, suggesting a new therapeutic opportunity for these disorders.

Amino Acid Sequence↗

PubMed1997

Machado-Joseph disease presenting as severe asymmetric proximal neuropathy.

Despite much effort, a 74 year old man with progressive proximal weakness and sensory disturbances due to axonal neuropathy remained a diagnostic problem. Investigation of his family disclosed an additional patient with a cerebellar syndrome and a family member with mainly pyramidal features. Analysis of DNA showed a CAG repeat expansion in the Machado-Joseph disease gene in all three patients. Although not conclusively proved, we think that the neuropathy of the index case is linked to the CAG repeat expansion. Machado-Joseph disease should be considered in progressive axonal neuropathy.

Adult↗

PubMed2004

The shortest expanded allele of the MJD1 gene in a Chinese MJD kindred with autonomic dysfunction.

Machado-Joseph disease (MJD) is the most common type of autosomal dominant spinocerebellar ataxia caused by an expanded CAG repeat in the MJD1 gene. Intermediate CAG alleles have been previously described, and they tend to be associated with unusual manifestations of the nervous system. Here we describe a Chinese kindred with hereditary spinocerebellar ataxia, in which the proband presented with autonomic dysfunction besides the typical features of MJD. DNA analysis confirmed the clinical diagnosis and revealed that the expanded CAG repeat number of the proband is 51, which is the shortest known causative expanded allele. These findings indicate that the clinical entity of MJD can occur with 51 trinucleotide repeats, and that the clinical features of MJD might cover a wider spectrum than previously believed. The high clinical pleomorphism and the phenomenon with the 51-CAG-repeat units caused the disease phenotype in our patient, but the normal phenotype in the individuals from another MJD family strongly supports that the MJD phenotype is modulated by modifier factors.

Alleles↗

PubMedDate not supplied

[Genetic factors in the onset of schizophrenia].

The importance of inheritance in the development of schizophrenia was recorded in classic papers by Kraepelin and Bleuler. These observations have been confirmed by the contemporary research. In this paper, we summarize the results of genetic-epidemiological studies that include family, twin and adoption studies, as well as the results of segregation analysis and molecular-genetic research. Family studies indicate increased morbidity risk in the relatives of patients with schizophrenia, that augments with the degree of relation. Twin studies also suggest the importance of genetic factors demonstrating higher rates of concordance for the disorder in monozygotic (MZ) than in dizygotic (DZ) twins and consistent MZ/DZ ratios across the studies. Adoption studies provide further evidence for genetic vulnerability, showing an association between biological relatives separated at birth. The concept of "schizophrenia spectrum" is based on the observation of the familial aggregation of several hierarchically defined disorders in relatives of schizophrenic probands. Schizophrenia, schizoaffective disorder, schizotypal and paranoid personality disorder, other nonaffective psychoses and psychotic affective disease, according to this concept, represent manifestations of varying severity, of the same underlying vulnerability, which is transmitted within families. The results of segregation analyses support rather polygenic than monogenic inheritance, if schizophrenia is genetically homogeneous. However, the possibility of genetic heterogeneity augments the interest for searching for vulnerability genes with linkage. The results of linkage studies, indicating association between schizophrenia and markers on chromosomes 5, 6, 8 and 22, have not yet been replicated on independent samples of probands. Recent findings indicate that schizophrenia may be caused by unstable DNA (the expansion of trinucleotide repeated sequences at the disease locus). This could explain the departure from Mendelian inheritance, highly variable phenotype and wide ranging age of onset in schizophrenia. Further research in this field could not only clarify the mode of the transmission of the liability for schizophrenia and the relationship of genetic and environmental factors in the development of the disorder, but also determine which characteristics, behavior and physiological variables schizophrenia genes code for. This would, in addition, contribute to our understanding of the biological basis of schizophrenia.

Humans↗

PubMed2001

Mismatch repair and microsatellite instability in esophageal cancer cells.

Using in vitro mismatch repair (MMR) assay, we have identified 3 of 22 esophageal cancer cell lines exhibiting reduced MMR activity. By means of gel-shift assay, decreased binding ability to GT mismatch and CA loop was observed in these 3 cell lines. However, we could not find any mutations in the hMSH2, hMSH3 and hMSH6 genes, the protein products of which exhibit mismatch binding activity in human cells. In addition, when using antibodies against 5 MMR-related proteins (hMSH2, hMSH3, hMSH6, hPMS2 and hMLH1), no aberrant expression was detected in any of them. When we examined 9 microsatellite loci in endogenous genomic DNA, these 3 esophageal cancer cell lines, deficient in MMR, did not exhibit microsatellite instability. However, when we examined the repetitious sequence on exogenous plasmid DNA which was introduced into these 3 esophageal cancer cells, the results suggested that MMR deficiency in esophageal cancer cells could result in moderate instability of the exogenous sequence.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Sleep apnea and respiratory dysfunction in congenital myotonic dystrophy.

A case of neonatal Myotonic Dystrophy (MD) is presented. A 35 week old 3570 g baby was born to a mother affected by MD and pregnancy-induced unstable diabetes. Soon after birth, he developed apnea, severe hypoglycemia, hypocalcemia, hypotonia and mild respiratory distress. His clinical course improved during the following days, but persistent episodes of desaturation and/or cyanosis did not subside; hypotonia was mild. A polysomnographic recording showed mixed central and obstructive apnea. DNA testing showed trinucleotide repeat expansion mutations diagnostic of MD. The baby was discharged with home-sleep monitoring and breast-feeding. Recurrent apnea/bradycardia was the main clinical feature in this case of congenital MD, with increased risk of an acute life-threatening event.

Humans↗

PubMed2002

[Familial chronic progressive blepharoptosis without other neurological symptoms: a new clinical entity?].

Nine patients over 5 generations developed progressive bilateral blepharoptosis from 40 to 50 years of age, suggesting that they had an autosomal dominantly inherited blepharoptosis. Except for the ptosis, they had no apparent neurological symptoms: normal ocular movement, no bulbar sign and no muscle weakness in the extremities. On laboratory examination, serum creatine kinase and blood lactate levels were within normal limits, and acetylcholine receptor antibody was not elevated. Electrophysiological studies including EMG and nerve conduction velocities were normal. Muscle biopsies from gastrocnemius and palpebral muscles were nondiagnostic with no ragged-red fibers nor rimmed vacuoles. Nuclear inclusions were not recognized by electron microscopy. Since none of patients examined had mitochondrial DNA deletions and GCG repeat expansion in the poly A binding protein P2 (PABP2) gene, this familial disorder is a unique blepharoptosis with no relationship to progressive external ophthalmoplegia or oculopharyngeal muscular dystrophy with PABP2 mutation.

Adult↗

PubMed2026

Targeting DNA mismatch repair in Huntington's disease.

Somatic expansion of the HTT CAG repeat is a key feature of Huntington's disease (HD) pathogenesis. Mismatch repair (MMR) enzymes drive this process through erroneous DNA repair, with variants in MMR genes modifying the onset and progression of disease features. Cell-type-specific CAG repeat sizing recently confirmed that elevated somatic expansion underlies the selective vulnerability of HD medium spiny neurons, with expansion beyond certain CAG thresholds associated with distinct stages of cellular pathogenesis. In this review, we synthesise insights from post-mortem brain tissue, cell systems, and mouse models, detailing key CAG repeat-length-dependent changes. In addition, we critically evaluate the MMR proteins MSH3, MLH3, and PMS1 as therapeutic targets for slowing somatic expansion and outline key safety considerations for emerging MMR-modulating approaches.

Huntington Disease↗

PubMed2025

Polygenic variants in DNA repair genes are associated with neurodevelopmental disorders, regression and increased burdens of somatic variants and short tandem repeat expansions.

PURPOSE: Developmental regression, characterized by the loss of acquired milestones, occurs in some individuals with neurodevelopmental disorders (NDDs); yet, its molecular basis remains unclear. Studies suggest that DNA damage repair (DDR) genes, such as FAN1, may protect against neurological dysfunction by modulating the somatic stability of short tandem repeats (STRs). This study explores the contribution of DDR gene variants in NDD cases presenting with regression. METHODS: We analyzed 1087 NDD patients, focusing on those carrying variants in DDR genes and presenting regression. We assessed the sensitivity to DNA damage using mitomycin C on lymphoblastoid cells. Somatic variants and STR expansions were evaluated through high-depth short-read genome sequencing. To further investigate the pathogenetic role of STR expansions, we performed long-read genome sequencing on the most severely affected proband. RESULTS: Probands with regression carried multiple DDR gene variants, several within the Fanconi anemia pathway. Their lymphoblastoid cells showed increased sensitivity to mitomycin C-induced cytotoxicity compared with parental and control samples. Probands with severe phenotypes and regression exhibited an accumulation of somatic variants and STR instability, enriched in neurodevelopmental genes. CONCLUSION: Our findings suggest that polygenic DDR gene variants may contribute to developmental regression in NDDs by promoting the accumulation of somatic variants and STR expansions.

Humans↗

PubMed1996

Analysis of germline variation at the FMR1 CGG repeat shows variation in the normal-premutated borderline range.

In order to characterize the dynamics of CGG repeat instability at the fragile X syndrome locus (FMR1 gene), we have used small pool PCR to estimate the mutation rate within germline (sperm) and somatic tissue (leukocytes) of two normal males, one carrying the most common 29 CGG repeats allele, the other carrying a borderline normal-premutated allele of 55 repeats. Large contractions and moderate expansions of the repeat were found in sperm and blood for the 55 repeat allele while almost no variation was found in sperm or blood with the 29 repeat allele. Somatic blood DNA exhibited fewer expansions and contractions than sperm. Contractions were more frequent than expansions, and all the expansions were found in the +4 to +10 repeats range, while most of the contractions were found in the -10 to -30 range, suggesting that a subset of contractions results from a distinct mechanism. These results also suggest that the dynamics of the CGG repeat could be partly due to germline instability within the high normal or premutated ranges.

Fragile X Messenger Ribonucleoprotein 1↗