Genetic counseling in Becker type X-linked muscular dystrophy. I. Theoretical considerations

The prior probability of any woman being a carrier for Becker muscular dystrophy (BMD) has been calculated. If mu is the mutation rate in female germ cells and v the mutation rate in male germ cells, this probability is 34/3 mu + 20/3v. For all X-linked diseases with a fitness f the prior probability (H) is: (formula; see text).     

Clinical studies in benign (Becker type) X-linked muscular dystrophy

Ten extensive families with benign (Becker type) X-linked muscular dystrophy have been studied, in which there was a total of 67 affected males. Reliable information was available on 41 of these males, 29 of whom were alive at the time of the study.
The disorder was characterised by a predominantly proximal myopathy, associated with pseudohypertrophy of the calf muscles, particularly in the early stages of the disease. The early development of contractures was not a feature of the disease in these families and cardiac involvement, when present, was a late manifestation. The clinical findings in these patients are discussed in detail and compared with those in a large unselected group of patients with Duchenne muscular dystrophy. The results indicate that the best criterion for distinguishing between these two disorders is the age of becoming chair-bound.
Electrocardiographic studies revealed no consistent abnormality and no evidence of an abnormal algebraic sum of the R and S waves in lead Vi, as is found in patients with Duchenne muscular dystrophy.
Serum creatine kinase levels are significantly elevated, particularly in the early stages of the disease, and in this way preclinical cases may be identified.     

Electromyographic pattern in Duchenne and Becker muscular dystrophy. Part II. Electromyographic pattern in Becker muscular dystrophy in comparison with Duchenne muscular dystrophy

BACKGROUND: The aim of this study was to compare the electromyographic pattern in Becker muscular dystrophy (BMD) with that found in Duchenne muscular dystrophy (DMD). MATERIAL AND METHOD: Fourteen men with BMD and 51 boys with DMD were investigated. Proximal muscles were examined: m. biceps brachii (BB) and m. rectus femoris (RF). They were divided according to the clinical criteria in two groups: of those with slight changes (group AB) and of those with severe abnormalities (CD). As in the Part I of the paper our own method of Functional-QEMG was applied in the CNEMG examination. RESULTS AND CONCLUSIONS: Spontaneous activity (fibrillations, complex repetitive discharges) was equally frequent in BMD and DMD. Linked potentials were rather frequent in either group. Myopathic features such as MUAPs low amplitude and area, polyphasic shape were seen in either condition, but more marked in DMD than in BMD. Evaluation of IP recordings revealed that IP amplitude (amplitude size) is low in DMD already at the early stage of lesion but normal or only slightly diminished in BMD. It might perhaps suggest different degrees of lesion in type II MUs between the compared types of muscular dystrophy.     

Unusual inheritance of Becker type muscular dystrophy.

A family with Becker type muscular dystrophy is described, in which two females were severely affected, giving the family tree the appearance of dominant inheritance.     

Becker muscular dystrophy: correlation of deletion type with clinical severity.

Molecular deletion screening with cDNA probes from the dystrophin gene was undertaken in patients with Becker muscular dystrophy from 58 separate families. Deletions were found in 41 (71%) of these families. Thirty-four (83%) of the deletions started in the same intron near the centre of the gene, and although there was no precise correlation between clinical severity and deletion pattern, the commonest deletion pattern, which was present in 49% of all deletion families, is associated with a mild phenotype.     

Genetic epidemiology of Duchenne and Becker muscular dystrophy in Slovenia

Most population studies on Duchenne (DMD) and Becker (BMD) muscular dystrophies predated the discovery of the gene and its product dystrophin. The diagnosis of these conditions and consequent epidemiological estimates were therefore limited to clinical criteria. In our study of the Slovene population the prevalence and cumulative incidence of DMD and BMD were calculated by including additional diagnostic tests: deletion screening in the dystrophin gene as well as dystrophin immunocytochemistry. The minimal prevalence rates, 2.9/100000 for DMD, 1.2/100000 for BMD, and the minimal cumulative DMD incidence rate of 13.8/100000 are in the range of lower estimates compared to studies world-wide. However, we found a high BMD cumulative incidence rate of 5.7/100000 and a high proportion of BMD versus DMD cumulative incidence rate (41.3%). Our results imply that the epidemiological figures for BMD might have been underestimated in the past.     

Prenatal diagnosis in Becker muscular dystrophy

Prenatal diagnosis in a pregnancy at risk for Becker muscular dystrophy is reported. The diagnosis was made prior to 12 weeks of gestation by typing a CVS sample for DNA markers.     

Genetic counseling of isolated carriers of Duchenne muscular dystrophy

It has recently become possible to detect female carriers of Duchenne muscular dystrophy with no affected male relative in the family. These “isolated carriers” represent about 10% of women with high serum creatine phosphokinase (CPK) levels and clinical evidence of a muscle disease. Most isolated carriers ascertained by clinical and/or CPK levels and diagnosed by dystrophin immunostaining of muscle biopsy show symptoms of a muscular dystrophy, and often carry the diagnosis of recessive “limb-girdle muscular dystrophy” prior to dystrophin analysis. It has been difficult to offer genetic counseling and prenatal diagnosis for Duchenne muscular dystrophy in the families of these isolated carriers, largely due to the difficulty in determining which of the dystrophin alleles segregating in the family harbors the mutation in the heterozygote. Here we report genetic counseling of three isolated carriers and their families. In two cases, prenatal diagnosis of at-risk pregnancies was conducted. We determined X inactivation patterns and inheritance of X chromosomes in each family, and used this information to define the at-risk dystrophin gene. In all three families, the mutation was a de novo event, two in the paternal germ-line, and one in the maternal germ-line. In each case we show that sibs of the heterozygous woman are at population risk, while pregnancies of each propositus are at high risk. Our results show that accurate genetic counseling and prenatal diagnosis can be offered to these families. © 1996 Wiley-Liss, Inc.     

Genetic counseling for childless women at risk for Duchenne muscular dystrophy.

The aim of the present study was to assess the impact of genetic counseling in young women at risk to have Duchenne muscular dystrophy (DMD) children prior to childbearing. A total of 263 potential DMD carriers, who had had genetic counseling and were given different genetic risks, were included in this investigation. Their reproductive outcome and future plans as well as their requests for DNA tests (for carrier detection and prenatal diagnosis) were analyzed according to genetic risk magnitude, comprehension of genetic counseling is- sues, family and personal history, socio-educational level, and subjective opinion about selective abortion. We noted that genetic risk magnitude had no significant influence on reproductive plans or outcome nor on the request for additional DNA testing, even considering only those clients with good comprehension and retention of issues discussed during genetic counseling. On the other hand, counselees who had more than one affected or at least one deceased DMD case in their family understood genetic counseling significantly better, suggesting that "learning with life" has a stronger impact than genetic counseling.     

Investigation of a female manifesting Becker muscular dystrophy.

Females manifesting Becker muscular dystrophy (BMD) are even more rarely observed than for the allelic condition Duchenne muscular dystrophy. The male proband has typical BMD with greatly raised CK activity and a myopathic muscle biopsy. His mother experienced walking difficulties from 35 years of age and has a myopathy with marked calf hypertrophy, a raised CK, and a myopathic muscle biopsy. Dystrophin analysis was undertaken on both the proband and his mother. Immunoblotting showed a protein of normal size but of reduced abundance in both. Immunocytochemical analysis in the proband indicated that the majority of the fibres showed weak dystrophin labelling and in his mother both dystrophin positive and dystrophin negative fibres were present. Non-random X inactivation at locus DXS255, was observed in DNA isolated from peripheral lymphocytes of the mother. Neither extended multiplex PCR performed on DNA from the proband nor analysis of lymphocyte derived mRNA showed a structural alteration in the dystrophin gene suggesting that an unusual mutation was responsible for BMD in this family.     

Canine X-linked muscular dystrophy as an animal model of Duchenne muscular dystrophy: a review.

Canine X-linked muscular dystrophy is a spontaneously occurring, progressive, degenerative myopathy of dogs that is clinically and pathologically similar to Duchenne muscular dystrophy in man. The molecular basis for the disease has been shown to be a lack of dystrophin, the protein product of the Duchenne muscular dystrophy gene. Breeding colonies of dystrophic dogs have been established. This report reviews the findings of genetic, clinical, pathologic, molecular biologic, and immunocytochemical studies of the canine model, and compares the features of the canine disease to those of Duchenne dystrophy in man.     

High frequency of de novo deletions in Mexican Duchenne and Becker muscular dystrophy patients. Implications for genetic counseling

Duchenne muscular dystrophy (DMD) is the most common lethal hereditary neuromuscular disease. As there is no effective treatment, accurate carrier detection is essential for genetic counseling and prevention. Although linkage analysis has been widely used for this purpose, being an indirect analysis it has several limitations. Using linkage analysis for carrier detection, we found serious limitations, mainly because 82.9% of all proposita were isolated cases. We used quantitative polymerase chain reaction for direct carrier detection in families with exon deletions and found a higher than expected frequency of de novo deletions (62.2%). Furthermore, only 20.7% of the mothers of isolated deletion DMD/Becker muscular dystrophy (BMD) patients were found to be carriers. This result suggests that the Mexican population has a high frequency of de novo DMD mutations.     

Genetic counseling for childless women at risk for Duchenne muscular dystrophy

The aim of the present study was to assess the impact of genetic counseling in young women at risk to have Duchenne muscular dystrophy (DMD) children prior to childbearing. A total of 263 potential DMD carriers, who had had genetic counseling and were given different genetic risks, were included in this investigation. Their reproductive outcome and future plans as well as their requests for DNA tests (for carrier detection and prenatal diagnosis) were analyzed according to genetic risk magnitude, comprehension of genetic counseling is- sues, family and personal history, socio–educational level, and subjective opinion about selective abortion. We noted that genetic risk magnitude had no significant influence on reproductive plans or outcome nor on the request for additional DNA testing, even considering only those clients with good comprehension and retention of issues discussed during genetic counseling. On the other hand, counselees who had more than one affected or at least one deceased DMD case in their family understood genetic counseling significantly better, suggesting that “learning with life” has a stronger impact than genetic counseling. Am. J. Med. Genet. 86:447–453, 1999. © 1999 Wiley-Liss, Inc.     

Comparative analysis between Duchenne and Becker types muscular dystrophy.

Duchenne and Becker types of muscular dystrophy are usually differentiated according to age of onset and rate of progression criteria which are not sufficient. The aim of this paper was to re-establish the clues for distinguishing Duchenne from Becker types of muscular dystrophy. According to the onset and progression of the disease, one hundred and eleven patients were subdivided into two groups. First group--Becker muscular dystrophy--consisted of 40 patients and second one of 71 patients with Duchenne type of muscular dystrophy. Clinical data confirm some well known differences between Duchenne and Becker muscular dystrophy concerning the age of onset, severity of disease and rate of progression. Electromyographic signs of myopathic changes and spontaneous activity were found in both diseases. Spontaneous activity--bizarre and fibrillation potentials, as well as sharp waves are more common for Duchenne type. The differences between the Becker from Duchenne type of muscular dystrophy can be described on the basis of complex investigations (clinical, electromyographical, histological and biochemical).     

Canine X-linked muscular dystrophy as an animal model of Duchenne muscular dystrophy: A review

Canine X-linked muscular dystrophy is a spontaneously occurring, progressive, degenerative myopathy of dogs that is clinically and pathologically similar to Duchenne muscular dystrophy in man. The molecular basis for the disease has been shown to be a lack of dystrophin, the protein product of the Duchenne muscular dystrophy gene. Breeding colonies of dystrophic dogs have been established. This report reviews the findings of genetic, clinical, pathologic, molecular biologic, and immunocytochemical studies of the canine model, and compares the features of the canine disease to those of Duchenne dystrophy in man.     

Genetic counselling in facioscapulohumeral muscular dystrophy.

Clinical data are presented from a survey of 41 families with dominantly inherited facioscapulohumeral muscular dystrophy (FSHD) in which over 500 family members were examined, including 168 affected subjects. New mutation could account for six isolated cases. Results suggest that 33% of heterozygotes over 40 years are mildly affected and a majority develop significant lower limb weakness; 19% over 40 years require wheelchairs. Presymptomatic testing of serum creatine kinase level (CK) is limited as a raised level occurs in only 80% of affected males under 40 years and 48% of affected women. Distribution of weakness, severity, age at onset, and CK varied between subjects, but provided no clinical evidence for genetic heterogeneity in a comparison between the 11 largest families. The conclusion of genetic homogeneity in FSHD, including subjects previously diagnosed as FSH type spinal muscular atrophy, is strongly supported by recent genetic linkage data.     

New type of X-linked progressive muscular dystrophy involving shoulder girdle and back

A new type of X-linked muscular dystrophy is described in a family in which 7 men had boyhood onset of progressive dystrophy involving muscles of the shoulder and back but not the calves or face. The scapula-back muscles are affected, but the calf muscles are normal. All patients are still able to walk. The oldest patient is now 37 years old. The muscular dystrophy has been specified by electromyography, pathologic tissue microscopic examination, electron microscopic study, and elevated CK. This type of muscular dystrophy has not been reported previously.