Paternal transmission of congenital myotonic dystrophy.

We report a rare case of paternally transmitted congenital myotonic dystrophy (DM). The proband is a 23 year old, mentally retarded male who suffers severe muscular weakness. He presented with respiratory and feeding difficulties at birth. His two sibs suffer from childhood onset DM. Their late father had the adult type of DM, with onset around 30 years. Only six other cases of paternal transmission of congenital DM have been reported recently. We review the sex related effects on transmission of congenital DM. Decreased fertility of males with adult onset DM and contraction of the repeat upon male transmission contribute to the almost absent occurrence of paternal transmission of congenital DM. Also the fathers of the reported congenitally affected children showed, on average, shorter CTG repeat lengths and hence less severe clinical symptoms than the mothers of children with congenital DM. We conclude that paternal transmission of congenital DM is rare and preferentially occurs with onset of DM past 30 years in the father.     

Paternal transmission of congenital myotonic dystrophy.

The congenital form of myotonic dystrophy is reported to be almost exclusively, if not exclusively, maternally transmitted. We present a case of congenital myotonic dystrophy which was inherited from a mildly affected father. This family illustrates that the congenital form of myotonic dystrophy can occur without intrauterine or other maternal factors related to the disease. The possibility of paternal transmission of the congenital form of myotonic dystrophy could be considered when counselling myotonic dystrophy patients and their families.     

Defective satellite cells in congenital myotonic dystrophy

In this study we have developed an in vitro cell culture system which displays the majority of the defects previously described for congenital myotonic dystrophy (CDM) muscle in vivo. Human satellite cells were isolated from the quadriceps muscles of three CDM fetuses with different clinical severity. By Southern blot analysis all three cultures were found to have approximately 2300 CTG repeats. This CTG expansion was found to progressively increase in size during the proliferative life span, confirming an instability of this triplet in skeletal muscle cells. The CDM myoblasts and myotubes also showed abnormal retention of mutant RNA in nuclear foci, as well as modifications in their myogenic program. The proliferative capacity of the CDM myoblasts was reduced and a delay in fusion, differentiation and maturation was observed in the CDM cultures compared with unaffected myoblast cultures. The clinical severity and delayed maturation observed in the CDM fetuses were closely reflected by the phenotypic modifications observed in vitro. Since the culture conditions were the same, this suggests that the defects we have described are intrinsic to the program expressed by the myoblasts in the absence of any trophic factors. Altogether, our results demonstrate that satellite cells are defective in CDM and are probably implicated in the delay in maturation and muscle atrophy that has been described previously in CDM fetuses.     

A case of paternally inherited congenital myotonic dystrophy.

We report two sisters with congenital myotonic dystrophy (CDM) born to a normal mother and an affected father. The congenitally affected daughters had symptoms from birth. The age of onset of DM in the father was 39 years. Analysis of the CTG trinucleotide expansion in this family showed increase in the repeat length with increasing severity, with the smallest expansion in the grandfather and the largest expansion in the younger of the two CDM sisters. This family shows that exceptionally it is possible for CDM to be inherited paternally and refutes the hypothesis that CDM is exclusively of maternal origin. This contradicts several of the previous hypotheses concerning the mechanisms by which the CDM phenotype arises.     

Detection of the CTG repeat expansion in congenital myotonic dystrophy

Summary Myotonic dystrophy (DM) is caused by an abnormal expansion of an unstable CTG trinucleotide repeat in the 3′ untranslated region of mRNA encoding a putative serine/threonine protein kinase. We analyzed 59 patients with DM (28 congenital DM families: 27 families with maternal transmission and 1 paternal transmission) and 27 normal control subjects to evaluate their CTG repeat size between DM patients and the normal controls, and to search for a correlation between the clinical characteristics of congenital DM (CDM) and CTG repeat expansions. Analysis was on the basis of the Southern blot and polymerase chain reaction (PCR) methods, and by direct sequencing of PCR amplified CTG repeats. Analysis of intergenerational differences in the CTG repeat size for mother-child pairs showed a positive correlation (y=1.0384x+1265.2,r ²=0.311). In addition to the strong parental bias, this group showed genetic anticipation. There was a significant correlation of the CTG repeat expansion with disease severity. The largest CTG repeat expansion (2,293 CTG repeats) on average belonged to the severe CDM group, and the smallest (129 CTG repeats) to the subclinical DM group. The mutant allele of an asymptomatic father in the paternally transmitted pedigree revealed 75 CTG repeats, demonstrating that he was a DM protomutation carrier.     

Contribution of molecular analyses to the estimation of the risk of congenital myotonic dystrophy.

A molecular analysis of the maternal and child CTG repeat size and intergenerational amplification was performed in order to estimate the risk of having a child with congenital myotonic dystrophy (CMD). In a study of 124 affected mother-child pairs (42 mother-CMD and 82 mother-non-CMD) the mean maternal CTG allele in CMD cases was three times higher (700 repeats) than in non-CMD cases (236 repeats). When the maternal allele was in the 50-300 repeats range, 90% of children were non-CMD. In contrast, when the maternal allele was greater than 300 repeats, 59% inherited the congenital form. Furthermore, the risk of having a CMD child is also related to the intergenerational amplification, which was significantly greater in the mother-CMD pairs than in the mother-non-CMD pairs. Although the risk of giving birth to a CMD child always exists for affected mothers, our data show that such a risk is considerably higher if the maternal allele is greater than 300 repeats.     

Segregation distortion in myotonic dystrophy.

Myotonic dystrophy (DM) is an autosomal dominant disease which, in the typical pedigree, shows a three generation anticipation cascade. This results in infertility and congenital myotonic dystrophy (CDM) with the disappearance of DM in that pedigree. The concept of segregation distortion, where there is preferential transmission of the larger allele at the DM locus, has been put forward to explain partially the maintenance of DM in the population. In a survey of DM in Northern Ireland, 59 pedigrees were ascertained. Sibships where the status of all the members had been identified were examined to determine the transmission of the DM expansion from affected parents to their offspring. Where the transmitting parent was male, 58.3% of the offspring were affected, and in the case of a female transmitting parent, 68.7% were affected. Studies on meiotic drive in DM have shown increased transmission of the larger allele at the DM locus in non-DM heterozygotes for CTGn. This study provides further evidence that the DM expansion tends to be transmitted preferentially.     

Intestinal pseudo-obstruction in myotonic dystrophy.

We describe four myotonic dystrophy (DM) patients who developed recurrent intestinal pseudo-obstruction. Some episodes were associated with gastroenteritis, while abdominal crowding may have occurred in one case during the third trimester of pregnancy. In most instances, however, no apparent cause could be identified. Intestinal pseudo-obstruction may occur at any stage of DM. In one of our cases intestinal pseudo-obstruction preceded significant muscle weakness by 15 years. Intestinal pseudo-obstruction is usually treated effectively with conservative measures. These include restriction of oral intake, intravenous fluids, and multiple enemas or colonoscopy. Improved intestinal function was noted in one case treated with the prokinetic agent cisapride. A partial sigmoid resection was performed in three cases with dolichomegacolon. No abnormalities were reported on histological examination. Since intestinal pseudo-obstruction is a rare complication of DM, it is of interest that two of our cases are sibs. Review of published reports showed several reports of familial occurrence of specific complications. These include cardiac conduction disturbances, focal myocarditis, mitral valve prolapse, pilomatrixomas, polyneuropathy, normal pressure hydrocephalus, and dilatation of the urinary tract. Myotonic dystrophy may show a tendency to familial clustering of organ specific involvement.     

Mitochondrial DNA does not appear to influence the congenital onset type of myotonic dystrophy.

Neither the maternal inheritance pattern nor the early onset of congenital myotonic dystrophy are fully explained. One possible mechanism is that mitochondrial DNA (mtDNA) mutations might interact with the DM gene product, producing an earlier onset than would otherwise occur. We have used Southern hybridisation to show that high levels of major rearrangements of mtDNA are not present in muscle of five and in blood of 35 patients with congenital myotonic dystrophy. We used sequence analysis to show that no one particular mtDNA morph appears to cosegregate with congenital onset. A minor degree of depletion of mtDNA compared with nuclear DNA was present in the muscle of five patients with congenital DM, but we propose that this is not the primary cause of the muscle pathology but secondary to it. We have not found evidence that mtDNA is involved in congenital myotonic dystrophy.     

Presymptomatic diagnosis of myotonic dystrophy.

The discovery of an expanded (CTG)n repeat sequence in myotonic dystrophy (DM) has greatly improved our ability to detect DM gene carriers who have few or none of the classical signs of this disorder. We report here our experience with two such groups of gene carriers. We used a PCR based protocol that should be especially sensitive to small increases in CTG triplet number which might escape detection by conventional Southern blot analysis. Our analyses show that on 100 non-DM chromosomes the number of CTG triplets ranged from five to 37. We then studied 17 obligate gene carriers aged 55 years and over who showed no muscle weakness. All of the gene carriers in this group showed a relatively small increase in the number of CTG triplets (52 to 90 CTG triplets) with limited somatic mosaicism. We subsequently studied 11 subjects (aged 19 to 36 years) who had previously been identified as gene carriers by genetic linkage studies, but who lacked diagnostic signs. In this prospectively studied group, nine subjects showed an expanded allele, confirming the earlier prediction from linked genetic markers. The other two subjects had only two normal alleles and no expanded allele. Revision of the clinical data casts doubt on the original diagnosis of DM in their families. Preferential amplification of the normal non-expanded allele was noted in three asymptomatic gene carriers in this study (as well as in two of their clinically affected relatives). We caution that, at least in our hands, the DM mutation can be confidently excluded by this PCR based method only if both normal alleles have been identified.(ABSTRACT TRUNCATED AT 250 WORDS)     

Monocyte IgG-Fc receptors in myotonic dystrophy.

The effect of affinity purified natural thymocytotoxic autoantibodies from New Zealand Black (NZB) mice (NTA-1 and NTA-2) against pre-T cells was studied. Pre-treatment of spleen cells from nu/nu mice or bone marrow cells from DBA/2 mice with NTA-1 and complement (C) or with NTA-2 and C markedly inhibited the induction of T cell markers with a thymic extract in vitro. The effect of NTA-2 and C was abolished by absorption of NTA-2 with neuraminidase treated thymocytes, whereas its effect was not abolished by absorption with intact thymocytes. The effect of NTA-1 and C was abolished by absorption of NTA-1 with either neuraminidase treated thymocytes or intact thymocytes. The effect of NTA-2 was inhibited by lactose whereas the effect of NTA-1 was not. These results suggest that NTA-2 specifically recognizes the cell surface characteristics of pre-T cells and blocks the differentiation pathway of T cells.     

Hyperinsulinemia in myotonic dystrophy: identity of the maternal factor causing the neonatal myotonic dystrophy syndrome

An environmental factor acting on the fetus is thought to cause a neonatal syndrome characterized by marked muscular hypotonia, lack of respiratory drive and feeding difficulties, in some infants born to mothers with myotonic dystrophy. Mortality is high, especially amongst those babies born prematurely, but muscle strength and tone improve rapidly in survivors. Nevertheless, most survivors have physical deformities and mental retardation and are thought to develop myotonic dystrophy later. We propose that alterations in maternal insulin secretion (usual in myotonic dystrophy subjects) alter fetal blood glucose and amino acid levels and retard growth and maturation of fetal skeletal muscle. This leads to severe muscular hypotonia in affected infants. Also, we suggest that infants who die during the perinatal period may not have inherited the defective autosomal dominant gene that causes myotonic dystrophy.     

Clinical evidence for heterogeneity in myotonic dystrophy.

In a study of 35 index patients who developed myotonic dystrophy between birth and 30 years (neonatal cases aware excluded), 30 could be categorised into two clinical types. The 13 type 1 patients had a more severe limb weakness, of patchy distribution, associated with proportional facial weakness. The 17 type 2 patients had a milder and more diffuse limb weakness; their facial weakness, however, was very pronounced and preceded the limb weakness by several years. All but one of the 25 affected relatives who were examined belonged to the same category as their index relative, providing evidence that the cause of the clinical heterogeneity was genetic. Subsequent observations showed that mental retardation, male infertility, and neonatally affected offspring were commoner in type 2 patients. Congenital myotonic dystrophy could occur among the offspring of either affected males or affected females, but neonatal symptoms were confined to the offspring of affected women. The overall risk for having neonatally affected offspring for this prospective study of young adult patients was 7 in 38, and for the offspring of affected females 7 in 27. The risk for having a surviving child whose mental or physical handicap or both required special schooling was 1 in 12 for males and 4 in 27 for females.     

Altered motor neuron excitability in myotonic dystrophy.

Using standard electrophysiologic techniques motor conduction velocity (MCV), motor action potential amplitude (Mmax), minimum F latency (Flat), maximum F amplitude (Fmax), F chronodispersion (Fdisp), Fmax/Mmax, and F persistence (Fpers) were measured in median, ulnar, peroneal, and tibial nerves (N = 60) in 15 patients with myotonic muscular dystrophy (DM). The results were compared to data from 80 nerves in 20 healthy controls. The DM group (mean age = 39.7 yrs, mean duration of symptoms = 20.8 yrs) had diminished or absent biceps, triceps, knee, and ankle reflexes but retained 4- or better strength (modified MRC Scale) in the respective muscles. Thirteen nerves in 6 patients had absent F waves. For the remaining 47 nerves, no statistically significant difference was noted in parameters primarily related to conduction through peripheral nerve fibers (MVC, Flat, Fdisp) or Fmax/Mmax. Fmax, Fpers and Mmax were significant (p less than or equal to .02) diminished in all nerve subgroups in the DM patients. The results indicate that in DM there is altered excitability of the motorneuron pool. This may underlie the early loss of DTR's and produce the characteristic distal pattern weakness.