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.     

Effects of genetic counseling on Duchenne muscular dystrophy families in Brazil

We report the preliminary results of a follow-up study of 574 females at-risk for Duchenne dystrophy, recontacted 3 to 13 yr after genetic counseling (GC). Among them, 290 are younger than 18 yr or still unmarried. The effectiveness of GC (reproductive performance) in the remaining group is analyzed in terms of procreation, rate of sterilization, and mean number of children. The observed data suggest that females at-risk involved in GC had about 169 children less than their normal, nonaffected brothers. In terms of prevention this would correspond roughly to 42 Duchenne affected boys and 42 carrier girls.     

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.     

A study of possible heterogeneity in Duchenne muscular dystrophy

One possible explanation for the apparently high birth incidence of Duchenne muscular dystrophy (DMD), a lethal X-linked disorder, is genetic heterogeneity. As a first step in possibly demonstrating genetic heterogeneity, affected boys were sub-divided into those with and without severe mental handicap. In those with severe mental handicap, ages at onset and of becoming confined to a wheelchair were later, the fall in SCK level with age was less marked, and the urinary excretion of certain aminoacids was greater than in affected boys with normal intelligence. Though the number of subjects investigated was relatively small (15 in each group) and further studies are therefore needed, the results suggest that DMD may not be a single disease entity.     

Improved detection of Duchenne muscular dystrophy heterozygotes using discriminant analysis of creatine kinase levels

We have assessed the sensitivity and specificity of tests to detect carriers of Duchenne muscular dystrophy by use of three serum enzymes (creatine kinase, pyruvate kinase, and aldolase) and discriminant analysis in 21 obligate heterozygotes and 28 normal controls. We found no significant age effects on enzyme levels. Each enzyme level considered separately was significantly higher in heterozygotes. Use of logs improved discrimination, and log CK was sufficient by itself as a discriminant (that is, addition of other enzymes did not significantly improve discrimination). We present procedures to generate posteriori probabilities for genetic counselling that incorporate prior probabilities and enzyme levels. Our results show both improved sensitivity (90%) and specificity (86%).     

Mutation and haplotype analysis for Duchenne muscular dystrophy by single cell multiple displacement amplification

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder with mutational heterogeneity. The scarcity of DNA from single cells in preimplantation genetic diagnosis (PGD) for DMD limits comprehensive genetic testing. Multiple displacement amplification (MDA) is reported to generate large amounts of template and give the most complete coverage and unbiased amplification to date. Here, we developed mutation and haplotype analysis in conjunction with gender determination on MDA products of single cells providing a generic approach that widens availability of PGD for female carriers with varied mutations. MDA amplified with 98.5% success for single lymphocytes and 94.2% success for single blastomeres, which was evaluated on 60 lymphocytes and 40 blastomeres. A total of six commonly mutant exons, eight short tandem repeat markers within dystrophin gene and amelogenin were incorporated into subsequent singleplex PCR assays. The mean allele dropout rate was 9.0% for single lymphocytes and 25.5% for single blastomeres. None of the blank controls gave a positive signal. Genotyping of each pedigree for three families provided 2-3 fully informative alleles per dystrophin haplotype besides specific mutant exons and amelogenin. We suggest that this approach is reliable to identify non-carrier female embryos other than unaffected male embryos and reduce the risk of misdiagnosis.     

女性假肥大型肌营养不良症家系的临床病理和基因分析

目的研究女性假肥大型肌营养不良症(Duchenne muscular dystrophy，DMD)患者的临床特征，探讨其发病机理。方法对一个女性DMD家系患者的临床表现进行跟踪随访，并作肌肉组织的免疫组化检测及基因分析。结果该家系的DMD患儿临床表现及辅助检查均符合典型的DMD特征。先证者母亲的临床特点类似良性假性肥大型肌营养不良(Becker muscular dystrophy，BMD)，肌肉免疫荧光分析提示dystrophin蛋白染色阳性的纤维与阴性纤维并存。该家系的dystrophin基因分析为非缺失型。先证者母亲核型分析正常。结论本家系中的39岁女性具有类似BMD的临床表现，病理检查及图像分析提示dystrophin蛋白为正常的1／3。此例女性患者的核型分析正常，故倾斜的X染色体模式为其可能的机理。     

Molecular deletions in the Duchenne/Becker muscular dystrophy gene

To gain further information relating to the frequency, position and size of DNA deletions in the Duchenne/Becker muscular dystrophy (D/BMD) gene region, and to detect any correlation of these deletions with phenotype, a large clinic-based population of DMD and BMD patients has been investigated using 13 cloned intragenic sequences. Our of 263 separate patients studied, 75 showed a deletion of at least one locus (28.5%). These represented 25.6% (55/215) of DMD patients and 41.7% (20/48) of BMD patients, suggesting that the milder phenotype is more often likely to be due to a deletion. The deletions range from 6 kilobases (kb) to greater than 1000 kb in size. The distribution of deletions across the gene region shows at least one region (detected by P20) prone to deletion mutations in both DMD and BMD patients. There is no simple correlation of position or extent of deletions with DMD or BMD, although deletion of a specific region towards the 5' end of the gene may be more often associated with a milder phenotype. Apparently similar deletions can give rise to phenotypes differing significantly in severity, presumably indicating further complexities in the molecular or cellular pathology.     

Recurrence risk due to germ line mosaicism: Duchenne and Becker muscular dystrophy

The presence of multiple affected offspring from apparently non-carrier parents is caused by germ line mosaicism. Although germ line mosaicism has been reported for many diseases, figures for recurrence risks are known for only a few of them. In X-linked Duchenne and Becker muscular dystrophies (DMD/BMD), the recurrence risk for non-carrier females due to germ line mosaicism has been estimated to be between 14% and 20% (95% confidence interval 3–30) if the risk haplotype is transmitted. In this study, we have analyzed 318 DMD/BMD cases in which the detected mutation was de novo with the aim of obtaining a better estimate of the 'true' number of germ line mosaics and a more precise recurrence risk. This knowledge is essential for genetic counseling. Our data indicate a recurrence risk of 8.6% (4.8–12.2) if the risk haplotype is transmitted, but there is a remarkable difference between proximal (15.6%) (4.1–27.0) and distal (6.4%) (2.1–10.6) deletions. Overall, most mutations originated in the female. Deletions occur more often on the X chromosome of the maternal grandmother, whereas point mutations occur on the X chromosome of the maternal grandfather. In unhaplotyped de novo DMD/BMD families, the risk of recurrence of the mutation is 4.3%.     

A survey of manifesting carriers of Duchenne and Becker muscular dystrophy in Wales

Manifesting carriers of Duchenne and Becker muscular dystrophy are uncommon but well described. Such patients are of particular importance with regard to the differential diagnosis from autosomal recessive limb-girdle muscular dystrophy. All mothers of affected males known to the Genetic Register of Muscular Dystrophy Families in Wales were contacted, and 167 out of a possible 190 were examined. It was estimated from pedigree and creatine kinase analysis that 119 out of the 167 were carriers of the Duchenne/Becker gene. Three manifesting carriers were identified, giving the proportion affected as 3/119 = 2.5%. We estimate the prevalence of manifesting carriers to be 1 in 100,000 of the female population, a figure comparable to the prevalence of autosomal recessive limb-girdle muscular dystrophy. During the period of the survey, several other women with similar clinical findings but without an appropriate family history were seen. We strongly suspect that some of these are also manifesting carriers of the Duchenne/Becker gene.     

Duchenne muscular dystrophy and myotonic dystrophy in the same patient

We report on the first patient identified with myotonic dystrophy and Duchenne muscular dystrophy (DMD). The family of the propositus had a strong history of myotonic dystrophy, and there was an intrafamilial pathological expansion of the responsible CTG repeat between the mildly affected mother (160 repeats; normal 27 repeats) and her more severely affected son (650 repeats), and his sister (650 repeats). The propositus was an isolated case of Duchenne muscular dystrophy with marked dystrophin deficiency in muscle biopsy. The patient was still ambulatory post age 16. Myotonic dystrophy could interfere to some extent with the progression of Duchenne dystrophy. However, other interpretations are possible. Twelve percent of dystrophin revertant fibers as observed by immunohistochemistry could be sufficient to ameliorate typical DMD clinical severity, or the patient may present a somatic mosaic. The pathophysiological interactions of these two unlinked disorders are discussed at the clinical and histopathological levels. © 1995 Wiley-Liss, Inc.     

杜氏进行性肌营养不良的临床实践指南

杜氏进行性肌营养不良(Duchemiemusculardystmphy.DMD)是最常见的X连锁隐性遗传性肌肉变性疾病,在男性新生儿中的发病率约为1/3500。DMD是由于Xp21.2区的抗肌萎缩蛋白基因(dystrop,DMD)突变所致,患者的主要临床表现包括进行性、对称性肌无力。由于呼吸肌和心肌受累,通常在30岁前死亡。通过基因检测,可以为93.1%的患者找到遗传学病因,为早期治疗和指导家庭成员的生育奠定基础,有利于改善患者的生存质量,预防这些家庭再次生育DMD患儿。本指南结合了国内外的相关研究和指南共识,总结了DMD相关的医学遗传学知识和临床处置要点,期望能给予临床工作者帮助,为DMD患者及其家庭提供规范的诊断、治疗和预防。     

外显子跳跃治疗Duchenne型肌营养不良症的研究进展

Duchenne型肌营养不良症是一种致死性肌肉疾病,抗肌萎缩蛋白基因缺陷是导致本病的原因,目前本病尚无特效的疗法.反义寡核苷酸(antisense oligonucleotides,AOs)诱导的外显子跳跃作为一种新的治疗手段具有良好的应用前景.本文主要从外显子跳跃治疗的原理、基础研究及临床研究进行综述.     

Germinal mosaicism in a Duchenne muscular dystrophy family: implications for genetic counselling

Melis MA, Cau M. Congiu R, Puddu R, Muntoni F, Cao A. Germinal mosaicism in a Duchenne muscular dystrophy family: implications for genetic counselling.
Clin Genet 1993: 43: 247–249. © Munksgaard, 1993
In this study we describe a three-generation family in which two siblings were affected by Duchenne muscular dystrophy (DMD). Immunohisto-chemical analysis of muscle dystrophin and haplotype analysis of the DMD locus revealed that the X chromosome carrying the DMD gene was transmitted from the healthy maternal grandfather to his three daughters. including the proband's mother. These findings indicate that the grandfather was a germinal mosaic for the DMD gene. The definition of the carrier status in two possible carriers led us to give accurate genetic counselling and to prevent the birth of an affected boy. The results of this study demonstrate the usefulness of haplotype analysis and immuno-histochemical muscle dystrophin studies to detect hidden germinal mosaicism and to improve genetic counselling.     

第二代测序技术在假肥大型肌营养不良基因诊断中的应用

目的 对假肥大型肌营养不良患者进行基因检测.方法 采用目标区序列捕获及第2代高通量测序技术对6例假肥大型肌营养不良患者进行检测;采用第1代测序技术、多重连接依赖的探针扩增技术(multiplex ligation-dependent probe amplification,MLPA)对患者及其母亲的基因型进行验证.结果 1例为第10和11外显子缺失,1例为第16和17外显子重复,4例为点突变.共发现10种变异:c.2776C＞T、c.5475delA、c.6391_ 6392delCA、IVS64+1G＞A、c.2645A＞G、c.5244G＞A、c.7728T＞C、c.8729A＞T、e.8734A＞G和c.8810G＞A,前4种为可疑致病性变异,后6种为人群中的多态.其中3例为首次发现的新突变(IVS64+1G＞A、c.6391_6392delCA(p.Q2131NfsX3)和p.Q926X(CAG＞TAG).结论 通过第2代测序技术可以在一个反应中准确检测出DMD基因的缺失、重复和点突变,具有一定的临床应用价值.     

Cytogenetic heterogeneity of translocations associated with Duchenne muscular dystrophy

Lymphoblastoid cell lines have been established from nine female patients with Duchenne muscular dystrophy who had previously been reported to have chromosome translocations with breakpoints in the Xp21 region. A detailed cytogenetic comparison of prometaphase chromosomes in these cell lines revealed that six of the translocations had X chromosome breakpoints in the sub-band Xp212 and that one further breakpoint could be assigned to either Xp212 or Xp213. These findings confirm and extend previous observations and provide strong evidence for Xp212 as the site of the Duchenne and Becker loci. For the remaining two translocations the simplest explanation for the observed banding pattern is that the X chromosome breakpoint lies a few thousand kilobases away, in the sub-band Xp211. Other explanations which assume breaks in Xp212 combined with complex local chromosome rearrangements are also presented. It is also possible that the altered banding pattern in these two cases is due to the influence of local sequences on the staining or uncoiling properties of the chromatin.     

Duchenne muscular dystrophy and spinal muscular atrophy type I segregating in the same family

We report on a family with two severe neuromuscular diseases: Duchenne muscular dystrophy (DMD) and acute infantile spinal muscular atrophy (SMA I). One boy has DMD, and his brother died of SMA I at 11 months of age. Both boys had received the same DMD allele from their mother. Analysis of dystrophin by immunohistochemistry and Western blot showed complete lack of dystrophin in both brothers. The mother had a partial deficiency of dystrophin. The boy with SMA I had increased levels of creatine kinase in serum, compatible with DMD, but the muscle biopsy and post-mortem examination of the spinal cord showed the typical changes of SMA I. There were no cytogenetic abnormalities explaining the occurrence of both DMD and SMA I in this family. Molecular genetic prenatal diagnosis of DMD and SMA I, using analysis of RFLPs and dinucleotide repeats, has been performed in one foetus in the family. The results showed that the foetus had a high risk of developing SMA I. An abortion was planned but the pregnancy was terminated by miscarriage.     

Specific detection of deleted and non-deleted dystrophin exons together with gender assignment in preimplantation genetic diagnosis of Duchenne muscular dystrophy

We have developed a preimplantation genetic diagnosis (PGD) strategy for Duchenne muscular dystrophy (DMD) allowing the simultaneous amplification of four exons (6, 8, 28 and 32) of the dystrophin gene together with ZFX/ZFY genes for gender determination. Preliminary experiments were carried out on 215 single lymphocytes from male and female individuals. Amplification rates ranged from 90.2% for exon 6 to 96.7% for exons 8 and 32. At least four of the five sequences were successfully amplified in 95.8% of single cells, and sexing was possible in 98.5%. This 5-plex assay was found to be robust enough to be used in a PGD clinical procedure and was therefore applied to a family whose female partner was a heterozygous carrier of a large deletion extending from exon 21 to exon 34 of the dystrophin gene. We have thus analysed two exons located in the deleted region of the gene, two non-deleted exons used as intrasample controls, and ZFX/ZFY genes. Cleavage stage embryo biopsy followed by PCR resulted in transfer of three unaffected embryos. The advantage of the present approach is to identify and subsequently transfer unaffected male embryos in addition to female embryos, and is now applicable to all families displaying a deletion involving at least one of these exons.     

Duchenne型肌营养不良症的细胞治疗

Duchenne型肌营养不良症（Duchenne muscular dystrophy，DMD）表现为进行性肌肉萎缩，是一种致死性、遗传性神经肌肉疾病。尽管对肌肉萎缩的分子机理的研究取得了很大进展，但是仍然不能治愈，细胞治疗是很有前景的一种治疗方法。成肌细胞移植面临的主要限制是注射后细胞分布差，免疫排斥和细胞存活率低；骨髓干细胞移植需要解决横向分化的低效率问题；而肌源性干细胞看来能更有效地再生表达dystrophin的肌纤维。     

Reproductive patterns among mothers of males diagnosed with Duchenne or Becker muscular dystrophy

Diagnosis of a child with Duchenne or Becker muscular dystrophy (DBMD) may impact future maternal reproductive choice; however, little is known about the reproductive patterns of mothers with a male child diagnosed with DBMD. Using population‐based surveillance data collected by the muscular dystrophy surveillance, tracking, and research network, the proportion of mothers who conceived and delivered a live birth following the diagnosis of DBMD in an affected male child and factors associated with such reproductive choice were identified. To accomplish this, maternal demographic data were linked to birth certificate data to construct the reproductive history for 239 mothers. Univariable and bivariable analyses were conducted to determine the proportion of mothers delivering a live birth and associated factors. By the time of the current study, 96 (40.2%) of the 239 mothers had at least one live birth following delivery of their oldest affected male child; 53 (22.2%) of these mothers had a live birth before and 43 (18.0%) had a live birth after DBMD diagnosis of a male child. Mothers with a live birth after diagnosis were significantly younger at diagnosis of the oldest affected male child (26.2 ± 4.2 years vs. 31.5 ± 5.5 years), and were less likely to be white non‐Hispanic compared to those with no live birth after diagnosis. These results suggest that about one in five mothers deliver a live birth subsequent to DBMD diagnosis in a male child. Maternal age and race/ethnicity were associated with this reproductive choice. © 2012 Wiley Periodicals, Inc.