Myotonic dystrophy phenotype without expansion of (CTG)n repeat: an entity distinct from proximal myotonic myopathy (PROMM)?

Myotonic dystrophy (DM) is associated with an expansion of an unstable (CTG)n repeat in the 3' untranslated region of the DM protein kinase (DMPK) gene on chromosome 19q13.3. We studied six patients from two families who showed no expansions of the repeat, in spite of their clinical diagnosis of DM. These patients had multi-systemic manifestations that were distinguishable from those seen in other myotonic disorders, including proximal myotonic myopathy (PROMM). In one additional family, two symptomatic members showed no expanded (CTG)n repeats, while their affected relatives had the expanded repeats. DM haplotype analysis failed to exclude the DMPK locus as a possible site of mutation in each family; however, DMPK mRNA levels were normal. We conclude that a mutation(s) other than the expanded (CTG)n repeat can cause the DM phenotype. The mutation(s) in these families remain(s) to be mapped and characterized.     

Brain disease and molecular analysis in myotonic dystrophy

Abnormal amplification of a CTG repeat on chromosome 19 is the molecular basis of myotonic dystrophy (DM). Expansion of the repeat has been correlated with severity of several clinical features of the disease. We performed extensive cognitive testing, cerebral magnetic resonance imaging (MRI) and a molecular analysis in 28 cases of DM to determine the relationship between the molecular defect and brain disease. Performance in two or more cognitive tests was pathological in 10 cases. Fourteen patients had subcortical white matter lesions on MRI, 14 had cerebral atrophy. Amplification of the CTG repeat showed a strong correlation with cognitive test deficits when exceeding a length of over 1000 trinucleotides. MRI lesions were associated with impaired psychometric performance, but MRI and molecular findings were only weakly related. Disease duration influenced the appearance and amount of white matter lesions on MRI. Quantification of CTG repeat size may allow an early estimate on the probability of brain involvement in DM; cognitive dysfunction is associated with white matter lesions and cerebral atrophy later on in the course.     

Instability of normal (CTG)n alleles in the DM kinase gene

We report on a myotonic dystrophy (DM) family exhibiting instability of normal sized (CTG)n alleles in the DM kinase gene on the non-DM chromosome. At least two mutational events involving normal DM alleles must have occurred in this family; one was characterised as a 34-35 (CTG)n repeat mutation. These findings represent a dissociation between (CTG)n repeat instability and myotonic dystrophy. Furthermore, this family highlights genetic counselling issues relating to the pathogenicity of alleles at the upper end of the normal size range and the risk of further expansion into the disease range.     

Normal levels of DM RNA and myotonin protein kinase in skeletal muscle from adult myotonic dystrophy (DM) patients

A major question about the pathogenesis of myotonic dystrophy (DM) is how the (CTG)n repeat mutation alters expression of the DM gene and how that is related to disease causation. Most previous studies have found a decrease in DM RNA and protein in patient tissue. In contrast to these reports we find, unexpectedly, that independent of the size of the CTG repeat: (1) there are equal levels of RNA products of mutant and normal alleles, and (2) levels of Mt-PK in skeletal muscle from DM patients is unaltered from normal. These findings are consistent with the recent hypothesis that mutant DM DNA or RNA may cause disease by disrupting the function of other, yet unidentified, genes.     

Somatic mosaicism of p(CTG)n expansion in a case of myotonic dystrophy with parotid tumor

Myotonic dystrophy (MD) is an autosomal dominant systemic disorder with an unstable expansion of the CTG triplet repeat in the 3'-untranslated region of the gene encoding myotonine protein kinase (DMPK) which maps to chromosome 19q13.3. Somatic mosaicism of CTG repeats in MD has been reported; and it has been observed that CTG repeats in tumor tissues associated with MD are more expanded than the other tissues. It is not rare that parotid tumors are found in patients with MD. We performed Southern blot analysis for tissues from the parotid tumor, the normal parotid gland, the skeletal muscles, and the leukocyte from a 60-year-old patient with MD. CTG repeat was most expanded in the parotid tumor, and the normal parotid gland had longer expansion of CTG repeat than the skeletal muscles. The leukocyte had the shortest expansion of CTG repeat. The expansion of CTG repeat in the parotid tumor may be related to active cell division and may underlie the occurrence of tumors in MD.     

Relative stability of a minimal CTG repeat expansion in a large kindred with myotonic dystrophy

The genetic basis for myotonic dystrophy (DM) is a CTG trinucleotide repeat expansion. The number of CTG repeats commonly increases in affected individuals of successive generations, in association with anticipation. We identified a large DM family in which multiple members had minimal CTG repeat expansions, and in which the number of CTG repeats remained in the minimally expanded range through at least three, and possibly four, generations. This relative stability of minimal CTG repeat expansions may help to maintain the DM mutation in the population.     

Human papillomavirus investigation of patients with cervical intraepithelial neoplasia 3, some of whom progressed to invasive cancer

Unstable expansion of the CTG repeats in the 3' untranslated region encoding a member of the protein kinase family in the q13.3 band on chromosome 19 is a mutation specific for myotonic dystrophy. To examine the correlation between clinical expression and CTG trinucleotide repeat length, we carried out Southern blot analysis in a family with myotonic dystrophy. In this pedigree, the expanded CTG repeats were transmitted maternally. The mother had three female children. The mother had about 200 CTG repeats, and the number of repeats for each child was about 800, 1500 and 1600 in birth order. The mother and the patient with 800 repeats were unaware of muscle weakness or myotonia. Symptoms were present from age 3 years in the patient with 1500 repeats and from birth in the one with 1600 repeats. Although the mother menstruated regularly, the patients with 800 and 1500 repeats both menstruated irregularly, and the one with 1600 repeats has never menstruated. The age of onset and severity of the disease were correlated with the size of the expanded repeats. Endocrinological studies revealed that the basal levels of the gonadotropins, PRL and E2 were within normal range, and a pituitary response to LHRH was observed. These data suggest that the amenorrhea and menstrual irregularities were caused by a suprahypophyseal dysfunction. When expanded CTG repeats are transmitted maternally, abnormal products resulting from the metabolic disturbance in the affected mother may harm the fetus in utero. A heterozygous fetus, who has more CTG repeats, may be unable to metabolize the pathologic products sufficiently and therefore may become more severely affected. This may explain the exclusive maternal transmission of congenital myotonic dystrophy.     

Urinary bladder wall repair: what suture to use?

We report the mapping of a second myotonic dystrophy locus, myotonic dystrophy type 2 (DM2). Myotonic dystrophy (DM) is a multi-system disease and the most common form of muscular dystrophy in adults. In 1992, DM was shown to be caused by an expanded CTG repeat in the 3' untranslated region of the dystrophia myotonica-protein kinase gene (DMPK) on chromosome 19 (refs 2-6). Although several theories have been put forth to explain how the CTG expansion causes the broad spectrum of clinical features associated with DM, it is not understood how this mutation, which does not alter the protein-coding region of a gene, causes an affect at the cellular level. We have identified a five-generation family (MN1) with a genetically distinct form of myotonic dystrophy. Affected members exhibit remarkable clinical similarity to DM (myotonia, proximal and distal limb weakness, frontal balding, cataracts and cardiac arrhythmias) but do not have the chromosome-19 D CTG expansion. We have mapped the disease locus (DM2) of the MN1 family to a 10-cM region of chromosome 3q. Understanding the common molecular features of two different forms of the disease should shed light on the mechanisms responsible for the broad constellation of seemingly unrelated clinical features present in both diseases.     

Anticipation and imprinting in schizophrenia

Anticipation, i.e., a decrease in the age of onset and/or an increase in the severity of a disease in subsequent generations, and imprinting, i.e., different modes of parental transmission, have been suggested in trinucleotide repeat amplification diseases. The purpose of this study was to determine if anticipation and imprinting are associated with familial schizophrenia. Two generations of 49 schizophrenics from 24 families were studied. Ages of onset, numbers hospitalized, diagnostic subclasses of schizophrenia, amounts of antipsychotics, positive symptoms, negative symptoms, treatment resistance, and clinical course ratings, were compared between the two generations. The age of onset was significantly lower in the offspring generation, although there was no difference in the severity between the two generations. The negative symptom scores and clinical course scores in the offspring generation for paternal transmission were significantly higher than those for maternal transmission. Our results suggest the presence of imprinting and anticipation in schizophrenia.     

Relationship between parental trinucleotide GCT repeat length and severity of myotonic dystrophy in offspring

OBJECTIVE: To assess the relationship between the GCT repeat number in the myotonic dystrophy gene and the clinical phenotype and examine its predictive utility in prenatal testing. DESIGN: DNA from patients was examined for the length of the myotonic dystrophy GCT repeat region, using both Southern blot analysis and polymerase chain reaction. The results were compared with the clinical onset of disease, as well as with pregnancy outcomes. SETTING: Patient samples were referred to the Kleberg DNA Diagnostic Laboratory at the Baylor College of Medicine for DNA analysis by geneticists and genetic counselors (84%), neurologists (10%), and obstetricians and other specialists (6%). Clinical features including onset of disease and family pedigrees were determined by the referring centers. PATIENTS: A total of 241 patient samples from 118 families referred from primarily genetic or neurological centers for genetic linkage analysis or mutation analysis for myotonic dystrophy. This included 44 families referred for prenatal diagnosis. MAIN OUTCOME MEASURES: A relationship between myotonic dystrophy disease onset and length of the GCT repeat allele, parental origin of the disease allele, and results of prenatal diagnosis predictions of disease status were measured. RESULTS: There is a relationship between increasing repeat length and earlier clinical onset of disease. Essentially all (> 99%) myotonic mutations causing myotonic dystrophy are accounted for by GCT repeat amplification. Congenital myotonic dystrophy occurs with as few as 730 GCT repeats but only with alleles of maternal origin. Maternal GCT repeats were found as low as 75 (asymptomatic) that were amplified to result in a child with congenital myotonic dystrophy. Application of DNA diagnosis to 32 pregnancies provided an accurate method for identification of at-risk fetuses and allele enlargement. CONCLUSIONS: The GCT repeat in myotonic dystrophy is highly mutable. The triplet repeat amplification is highly specific for mutations involving the myotonin protein kinase gene accounting for myotonic dystrophy. The quantitation of triplet repeats can be more sensitive than physical, ophthalmologic, and electromyography examinations since the mutation can be detected in patients without evidence of myotonic dystrophy clinical findings. The length of the triplet expansion is influenced by the sex of the transmitting parent and is related to the clinical onset of disease features. Prenatal measurement of the GCT triplet repeat has utility for families with myotonic dystrophy risk since mutant and normal repeats are distinguishable and the length of mutant repeat alleles is associated with clinical severity. Thus, GCT triplet measurement provides a highly accurate means of detecting the myotonic dystrophy mutation in patients and offers a new reproductive option for families at risk for myotonic dystrophy.     

Fluorescence in situ hybridization analysis of the replication properties of the myotonic dystrophy protein kinase (DMPK) gene region

Myotonic dystrophy (DM) is caused by an expansion of a CTG repeat sequence in the 3' noncoding region of a protein kinase gene (DMPK) at 19q13.3. We used in situ hybridization to analyse the replication timing of the genomic region containing DMPK in fibroblasts and myoblasts from controls and myotonic dystrophy patients. In this method the relative proportion of singlet to doublet hybridization signals is used to infer the relative time of replication of specific loci or regions. Our results show that in cells from normal individuals approximately 65% of signals appear as doublets, indicating early replication. In DM patients with a number of CTG repeats ranging from about 600-1800 we observed a significant increase of singlet-doublets compared to the background level. These results suggest the existence of replication alternations and/or structural differences between the normal and mutant alleles induced by the presence of the DM mutation.     

Expression of myotonic dystrophy protein kinase gene during in vivo and in vitro mouse myogenesis

Myotonic dystrophy (DM) is an autosomal dominant neuromuscular disorder characterized by a great variability in its clinical manifestations. The mutational basis underlying DM consists of an unstable (CTG)n trinucleotide repeat in the 3' untranslated region of the myotonic dystrophy protein kinase gene (DMPK). Conflicting results on DMPK gene expression in congenitally affected infants (CDM) have been published. Moreover, the prominence of satellite cells seen in muscle of CDM infants supports the notion that the congenital form is associated with an arrest in muscle development and suggests a role for the DMPK gene during differentiation and maturation of muscle. In order to clarify these findings, a comparative study of DMPK and myogenic factor mRNA levels was performed in developing mouse muscle tissues and cultured muscle cells at different developmental stages. Results show that DMPK gene expression is upregulated at a late stage of muscular development. This upregulation does not seem to depend on a given muscle specific bHLH factor.     

Diameter of the inferior vena cava as an index of dry weight in patients undergoing CAPD

Trinucleotide microsatellites are widespread in the human and other mammalian genomes. Expansions of unstable trinucleotide repeats have been associated so far with a number of different genetic diseases including fragile X, myotonic dystrophy (DM) and Huntington disease. While ten possible trinucleotides can occur at the DNA level, only CTG and CCG repeats are involved in the disorders described so far. However, the repeat expansion detection (RED) technique has identified additional large repeats of ATG, CCT, CTT, and TGG of potentially pathological significance in the human genome. We now show that conclusive information about the chromosomal localization of long trinucleotide repeats can be achieved in a relatively short time using fluorescence in situ hybridization (FISH) with biotin-labelled trinucleotide polymers. Large CTG expansions (> 1 kb) in DM and an unstable (CTG)306 repeat in a patient with schizophrenia were detected by eye through the microscope without electronic enhancement. Digital imaging was used to analyse the chromosomal distribution of long CCA and AGG repeats. Our results suggest that long trinucleotide repeats occur in the normal human genome and that the size of individual repeat loci may be polymorphic.     

Abnormal calcium metabolism in myotonic dystrophy as shown by the Ellsworth-Howard test and its relation to CTG triplet repeat length

Myotonic dystrophy (DM) is an autosomal dominant disorder characterized by peculiar clinical features. Its molecular basis is the unstable expansion of a CTG triplet repeat in the gene encoding myotonin protein kinase (Mt-PK), the nucleotide sequence of which has extensive homology to the cyclic AMP (cAMP)-dependent protein kinase gene. Extensive efforts have been made to clarify the signal transduction pathway in which the responsible gene operates, but confirming evidence has yet to be obtained. Because some symptoms in DM are similar to those in hypoparathyroidism, we divided 24 DM patients into two groups on the basis of their serum calcium levels; Group 1, those with normocalcemia (11 patients), and group 2, those with hypocalcemia (13 patients). The highly sensitive parathyroid hormone (HS-PTH) plasma levels in group 1 were within normal limits, whereas those in group 2 were abnormally high. Laboratory findings for the group 2 patients resembled those for pseudohypoparathyroidism (PHP), whereas those for group 1 patients were normal. The Ellsworth-Howard (EH) test was used to determine which type of PHP the group 2 patients belonged to. Both the phosphaturic (delta P) and urinary cAMP (UcAMP) responses were estimated. The delta P responses in group 2 were significantly lower than those in group 1, but their UcAMP responses did not differ. This is evidence that group 2 patients had PHP type II, whereas group 1 patients were normal. We also investigated whether the disease severity differed between the groups. Cataracts, ectopic calcifications, and ossifications, which are associated with PHP, were more frequent in group 2. In addition, the mean IQ in that group was significantly lower. Clinically, the group 2 signs agreed well with those of PHP, whereas for group 1 there was only a slight similarity. These results are additional evidence that the patients in group 2 have abnormal calcium metabolism, the abnormality being in the postadenylate cyclase-cAMP pathway in the renal tubular cells. The degree of (CTG)n expansion, the so-called expanded DNA fragment (EF) size, was determined by standard Southern blot analysis. The allelic EF sizes in both groups were greater than in the healthy controls. Moreover, those in group 2 were significantly longer than those in group 1. We therefore investigated whether EF size is correlated with the serum calcium and plasma PTH levels, the delta P responses in the EH test, and IQ. All these items were significantly correlated with EF size. Our findings show that the expanded DNA fragment size in DM is correlated with the degree of abnormal calcium metabolism.     

Analysis of germline mutation spectra at the Huntington's disease locus supports a mitotic mutation mechanism

Trinucleotide repeat disease alleles can undergo 'dynamic' mutations in which repeat number may change when a gene is transmitted from parent to offspring. By typing >3500 sperm, we determined the size distribution of Huntington's disease (HD) germline mutations produced by 26 individuals from the Venezuelan cohort with CAG/CTG repeat numbers ranging from 37 to 62. Both the mutation frequency and mean change in allele size increased with increasing somatic repeat number. The mutation frequencies averaged 82% and, for individuals with at least 50 repeats, 98%. The extraordinarily high mutation frequency levels are most consistent with a mutation process that occurs throughout germline mitotic divisions, rather than resulting from a single meiotic event. In several cases, the mean change in repeat number differed significantly among individuals with similar somatic allele sizes. This individual variation could not be attributed to age in a simple way or to ' cis ' sequences, suggesting the influence of genetic background or other factors. A familial effect is suggested in one family where both the father and son gave highly unusual spectra compared with other individuals matched for age and repeat number. A statistical model based on incomplete processing of Okazaki fragments during DNA replication was found to provide an excellent fit to the data but variation in parameter values among individuals suggests that the molecular mechanism might be more complex.     

Comparison of multisystemic therapy and parent training in the brief treatment of child abuse and neglect.

This study evaluated the relative efficacy of two promising treatments of child abuse and child neglect: parent training and multisystemic therapy. Subjects included 18 abusive families and 15 neglectful families who were randomly assigned to the treatment conditions. Self-report and observational measures were used to evaluate the effects of treatment at three levels that have been associated with child maltreatment: individual functioning, family relations, and stress/social support. Statistical analyses revealed that families who received either treatment showed decreased parental psychiatric symptomology, reduced overall stress, and a reduction in the severity of identified problems. Analyses of sequential observational measures revealed that multisystemic therapy was more effective than parent training at restructuring parent–child relations. Parent training was more effective than multisystemic therapy at reducing identified social problems. The differential influences of the two treatments were probably associated with differences in their respective treatment contexts and epistemologies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Expanding complexity in myotonic dystrophy

Myotonic dystrophy (DM) is a highly variable multisystemic disease belonging to the rather special class of trinucleotide expansion disorders. DM results from dynamic expansion of a perfect (CTG)n repeat situated in a gene-dense region on chromosome 19q. Based on findings in patient materials or cellular and animal models, many mechanisms for the causes and consequences of repeat expansion have been proposed; however, none of them has enjoyed prolonged support. There is now circumstantial evidence that long (CTG)n repeats may affect the expression of any of at least three genes, myotonic dystrophy protein kinase (DMPK), DMR-N9 (gene 59), and a DM-associated homeodomain protein (DMAHP). Furthermore, the new findings suggest that DM is not a simple gene-dosage or gain-or-loss-of-function disorder but that entirely new pathological pathways at the DNA, RNA, or protein level may play a role in its manifestation.     

Somatic instability of the myotonic dystrophy (CTG)n repeat during human fetal development

Myotonic dystrophy is characterised by the striking level of somatic heterogeneity seen between and within tissues of the same patient, which probably accounts for a significant proportion of the pleiotropy associated with this disorder. The congenital form of the disease is associated with the largest (CTG)n repeat expansions. We have investigated the timing of instability of myotonic dystrophy (CTG)n repeats in a series of congenitally affected fetuses and neonates. We find that during the first trimester the repeat is apparently stable and that instability only becomes detectable during the second and third trimesters. In our series repeat instability is apparent only after 13 weeks gestational age and before 16 weeks. The appearance of heterogeneity shows some tissue specificity, with heart most commonly having the largest expansion. The degree of heterogeneity is not correlated with initial expansion size as gauged by chorionic villus and blood (CTG)n repeat sizes.     

Heterogeneity of DM kinase repeat expansion in different fetal tissues and further expansion during cell proliferation in vitro: evidence for a casual involvement of methyl-directed DNA mismatch repair in triplet repeat stability

We have analysed the mitotic behaviour of expanded CTG repeats in somatic tissues and cultured somatic cells from myotonic dystrophy (DM) fetuses using indirect and direct methods. Heterogeneity of expansions between fetal tissues was demonstrated in a 16 week old fetus whereas there was no evidence for such a somatic heterogeneity in a 13 week old fetus. Dilution plating of cultured cells from an adult patient and a fetus resulted in isolation of clones showing single expanded restriction fragments when the donor showed a heterogeneous smear of expansions or a single expanded fragment. During proliferation in vitro to 45 doublings, DM cells experienced highly synchronous further repeat expansion which first became evident at approximately 15 cell generations and reached a plateau of maximum expansion at approximately 200 days. When mathematically expressed as a function of culture time the dynamics of expansion of restriction fragments followed a sigmoid curve. This unstable behaviour of CTG repeat expansions in DM was compared to the mitotically stable patterns of full mutation in fragile X fetal tissues and led to the hypothesis that methylation of CpGs within the repeat sequence is a stabilizing factor of largely expanded CGG and GCC repeats allowing for efficient methyl-directed strand-specific DNA mismatch repair.