Segregation analysis of 1885 DMD families: significant departure from the expected proportion of sporadic cases

A retrospective cohort study and review of the literature about germline mosaicism in Duchenne/Becker muscular dystrophy prenatal counseling: How to estimate the recurrence risk in clinical settings?

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are the most common inherited neuromuscular diseases. Following the identification of a pathogenic causative variant in the DMD gene of a proband, potential carriers can be informed of their risk of having offspring with the disease. Germline mosaicism is a variant that is confined to the gonads that can be transmitted to offspring and is usually reported when a non-carrier of a DMD pathogenic variant has two or more offspring carrying the variant in question. On average, one third of cases are the result of a de novo variant, and as DMD and BMD are prone to germline mosaicism, its inclusion in genetic counseling is mandatory. In this retrospective cohort study, we presented clinical data from an unpublished DMD/BMD cohort of 332 families with incidence of germline mosaicism in families with de novo transmission of 8.1%. This is also the first systematic literature review searching PubMed to provide an accurate assessment of the current literature on germline mosaicism in DMD and BMD, including 17 case reports and 20 original studies. The incidence of documented germline mosaicism in de novo event families ranged from 6.0 to 40%, with a mean of 8.3%. The estimated recurrence risk for mothers of a patient with a proven de novo causal variant ranged from 4.3 to 11%, with a mean of 5.8% for a male fetus. By providing an up-to-date and comprehensive overview of the literature, this review aims to improve our understanding of germline mosaicism in DMD and to promote the development of effective strategies and reliable data for occurrence risk assessment in genetic counseling of de novo event families.

Incidence of Duchenne muscular dystrophy in the modern era; an Australian study

Duchenne muscular dystrophy (DMD), an X-linked recessive condition is maternally inherited in two-thirds of affected boys. It is important to establish carrier status of female relatives to restore reproductive confidence for non-carriers and facilitate reproductive options and cardiac surveillance for carriers. This study investigates disease incidence within an Australian model of cascade screening and evolving genetic diagnostic technologies. A retrospective population-based cohort study of all genetically and/or histopathologically confirmed males with DMD, born in New South Wales and the Australian Capital Territory was undertaken from 2002-2012. Cases were identified using state-wide molecular laboratory and clinical databases. The annual disease incidence and "theoretically" preventable cases were extrapolated over the study period. Proband genotype/phenotype, pedigree analysis, carrier-risk and extent of cascade screening were also determined. The cumulative incidence of disease was 19.7 per 100,000 male live births and 1 in 5076 live born males were diagnosed with DMD. Differences in disease incidence were not statistically different when compared between 2002-2007 and 2008-2012 (incidence rate ratio = 1.13, 95% CI 0.76-1.69, p = 0.52). The incidence rate ratio of theoretically preventable cases did not significantly change between 2002-2007 and 2008-2012 (incidence rate ratio = 2.07, 95% CI 0.58-9.21, p = 0.23). Current diagnostic and cascade screening models have limitations in their impact on disease incidence, due to a spectrum of logistical, patient and condition related factors. Innovative approaches to reduce DMD incidence may be better achieved by preconception or early pregnancy carrier screening, prenatal exome sequencing and newborn screening.

N, Ramprasad VL, Gupta R, Seshagiri S, Nongthomba U, Phalke S. Matrilineal analysis of mutations in the DMD gene in a multigenerational South Indian cohort using DMD gene panel sequencing

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked recessive neuromuscular disorder characterised by progressive irreversible muscle weakness, primarily of the skeletal and the cardiac muscles. DMD is characterised by mutations in the dystrophin gene, resulting in the absence or sparse quantities of dystrophin protein. A precise and timely molecular detection of DMD mutations encourages interventions such as carrier genetic counselling and in undertaking therapeutic measures for the DMD patients.

RESULTS

In this study, we developed a 2.1 Mb custom DMD gene panel that spans the entire DMD gene, including the exons and introns. The panel also includes the probes against 80 additional genes known to be mutated in other muscular dystrophies. This custom DMD gene panel was used to identify single nucleotide variants (SNVs) and large deletions with precise breakpoints in 77 samples that included 24 DMD patients and their matrilineage across four generations. We used this panel to evaluate the inheritance pattern of DMD mutations in maternal subjects representing 24 DMD patients.

CONCLUSION

Here we report our observations on the inheritance pattern of DMD gene mutations in matrilineage samples across four generations. Additionally, our data suggest that the DMD gene panel designed by us can be routinely used as a single genetic test to identify all DMD gene variants in DMD patients and the carrier mothers.

Mosaicism in carrier of Duchenne muscular dystrophy mutation - Implication for prenatal diagnosis

OBJECTIVE

Duchenne muscular dystrophy (DMD) is a severe disorder caused by mutation in the X-linked dystrophin gene, therefor carrier testing is required for all female family members. However, there are cases mutation analysis cannot detect any mutation due to a phenomenon called mosaicism. The case report describes a case of mosaicism in a DMD carrier and discusses the approach in diagnosis and counseling of familial disorder.

CASE REPORT

The proband was diagnosed with DMD at age six. Sequencing of Dystrophin gene identified a 2-nucleotide deletion c.2032_2033delCA, p.Q678DfsX41. Family investigation suggested that the mother was an obligate carrier of Dystrophin mutation. Sequencing of DNA sample from the mother's peripheral blood did not reveal any mutation, there for we take sample from hair follicle for analysis. The result indicated that the mother was a carrier but was masked from initial analysis by mosaicsism.

CONCLUSION

We suggested that more care need to be taken in identifying cases when no mutation was detected in probable or obligate carrier and prenatal diagnosis should remain an option.

ECM-Related Myopathies and Muscular Dystrophies: Pros and Cons of Protein Therapies

Extracellular matrix (ECM) myopathies and muscular dystrophies are a group of genetic diseases caused by mutations in genes encoding proteins that provide critical links between muscle cells and the extracellular matrix. These include structural proteins of the ECM, muscle cell receptors, enzymes, and intracellular proteins. Loss of adhesion within the myomatrix results in progressive muscle weakness. For many ECM muscular dystrophies, symptoms can occur any time after birth and often result in reduced life expectancy. There are no cures for the ECM-related muscular dystrophies and treatment options are limited to palliative care. Several therapeutic approaches have been explored to treat muscular dystrophies including gene therapy, gene editing, exon skipping, embryonic, and adult stem cell therapy, targeting genetic modifiers, modulating inflammatory responses, or preventing muscle degeneration. Recently, protein therapies that replace components of the defective myomatrix or enhance muscle and/or extracellular matrix integrity and function have been explored. Preclinical studies for many of these biologics have been promising in animal models of these muscle diseases. This review aims to summarize the ECM muscular dystrophies for which protein therapies are being developed and discuss the exciting potential and possible limitations of this approach for treating this family of devastating genetic muscle diseases. © 2017 American Physiological Society. Compr Physiol 7:1519-1536, 2017.

Cognitive dysfunction in Duchenne muscular dystrophy: a possible role for neuromodulatory immune molecules

Duchenne muscular dystrophy (DMD) is an X chromosome-linked disease characterized by progressive physical disability, immobility, and premature death in affected boys. Underlying the devastating symptoms of DMD is the loss of dystrophin, a structural protein that connects the extracellular matrix to the cell cytoskeleton and provides protection against contraction-induced damage in muscle cells, leading to chronic peripheral inflammation. However, dystrophin is also expressed in neurons within specific brain regions, including the hippocampus, a structure associated with learning and memory formation. Linked to this, a subset of boys with DMD exhibit nonprogressing cognitive dysfunction, with deficits in verbal, short-term, and working memory. Furthermore, in the genetically comparable dystrophin-deficient mdx mouse model of DMD, some, but not all, types of learning and memory are deficient, and specific deficits in synaptogenesis and channel clustering at synapses has been noted. Little consideration has been devoted to the cognitive deficits associated with DMD compared with the research conducted into the peripheral effects of dystrophin deficiency. Therefore, this review focuses on what is known about the role of full-length dystrophin (Dp427) in hippocampal neurons. The importance of dystrophin in learning and memory is assessed, and the potential importance that inflammatory mediators, which are chronically elevated in dystrophinopathies, may have on hippocampal function is also evaluated.

Genetics and emerging treatments for Duchenne and Becker muscular dystrophy

Mutations in the DMD gene result in Duchenne or Becker muscular dystrophy due to absent or altered expression of the dystrophin protein. The more severe Duchenne muscular dystrophy typically presents around ages 2 to 5 with gait disturbance, and historically has led to the loss of ambulation by age 12. It is important for the practicing pediatrician, however, to be aware of other presenting signs, such as delayed motor or cognitive milestones, or elevated serum transaminases. Becker muscular dystrophy is milder, often presenting after age 5, with ambulation frequently preserved past 20 years and sometimes into late decades.

Identification of de novo mutations of Duchénnè/Becker muscular dystrophies in southern Spain

BACKGROUND

Duchénnè/Becker muscular dystrophies (DMD/BMD) are X-linked diseases, which are caused by a de novo gene mutation in one-third of affected males. The study objectives were to determine the incidence of DMD/BMD in Andalusia (Spain) and to establish the percentage of affected males in whom a de novo gene mutation was responsible.

METHODS

Multiplex ligation-dependent probe amplification (MLPA) technology was applied to determine the incidence of DMD/BMD in 84 males with suspicion of the disease and 106 female relatives.

RESULTS

Dystrophin gene exon deletion (89.5%) or duplication (10.5%) was detected in 38 of the 84 males by MLPA technology; de novo mutations account for 4 (16.7%) of the 24 mother-son pairs studied.

CONCLUSIONS

MLPA technology is adequate for the molecular diagnosis of DMD/BMD and establishes whether the mother carries the molecular alteration responsible for the disease, a highly relevant issue for genetic counseling.

Muscular dystrophies and other genetic myopathies

With advances in the genetics of muscle disease, the term, muscular dystrophy, has expanded to include mutations in an increasing large list of genes. This review discusses the genetics, pathophysiology, and potential treatments of the most common forms of muscular dystrophy: Duchenne muscular dystrophy, Becker muscular dystrophy, facioscapulohumeral muscular dystrophy, and myotonic dystrophy. Other forms of muscular dystrophy and other genetic muscle disorders are also discussed to provide an overview of this complex clinical problem.

Skipping multiple exons of dystrophin transcripts using cocktail antisense oligonucleotides

Duchenne muscular dystrophy (DMD) is one of the most common and lethal genetic disorders, with 20,000 children per year born with DMD globally. DMD is caused by mutations in the dystrophin (DMD) gene. Antisense-mediated exon skipping therapy is a promising therapeutic approach that uses short DNA-like molecules called antisense oligonucleotides (AOs) to skip over/splice out the mutated part of the gene to produce a shortened but functional dystrophin protein. One major challenge has been its limited applicability. Multiple exon skipping has recently emerged as a potential solution. Indeed, many DMD patients need exon skipping of multiple exons in order to restore the reading frame, depending on how many base pairs the mutated exon(s) and adjacent exons have. Theoretically, multiple exon skipping could be used to treat approximately 90%, 80%, and 98% of DMD patients with deletion, duplication, and nonsense mutations, respectively. In addition, multiple exon skipping could be used to select deletions that optimize the functionality of the truncated dystrophin protein. The proof of concept of systemic multiple exon skipping using a cocktail of AOs has been demonstrated in dystrophic dog and mouse models. Remaining challenges include the insufficient efficacy of systemic treatment, especially for therapies that target the heart, and limited long-term safety data. Here we review recent preclinical developments in AO-mediated multiple exon skipping and discuss the remaining challenges.

Neuropsychological profile of duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is an inherited myogenic disorder characterized by progressive muscle wasting. DMD is a fatal X-linked recessive disorder with an estimated prevalence of 1 in 3,500 male live births. This disease has long been associated with intellectual impairment. Research has shown that boys with DMD have variable intellectual performance, indicating the presence of specific cognitive deficits. The aim of the study was to use a battery of intelligence, learning, and memory tests to identify a neuropsychological profile in boys with DMD. A total of 22 boys diagnosed with DMD in the age range of 6 to 10 years old were evaluated using the Wechsler Intelligence Scale for Children-Third Edition, Rey's Auditory Verbal Learning Test, and the Memory for Designs Test. The data were interpreted using means, standard deviations, percentages, and percentiles. Normative data were also used for further interpretation. The results showed that boys with DMD had a significantly lower IQ (88.5). Verbal IQ (86.59) was found to be lower than Performance IQ (92.64). There was evidence of impaired performance on the Processing Speed, Freedom From Distractibility, and Verbal Comprehension Indexes. Specific deficits in information processing, complex attention, immediate verbal memory span, verbal working memory, verbal comprehension, vocabulary, visuoconstruction ability, and verbal learning and encoding were observed. However, perceptional organization, general fund of information, abstract reasoning, visual discrimination and acuity, visual learning and memory, and verbal memory were adequate. The neuropsychological findings support the hypothesis that these children have specific cognitive deficits as opposed to a global intellectual deficit.

Symptomatic female carriers of Duchenne muscular dystrophy (DMD): genetic and clinical characterization

Duchenne muscular dystrophy (DMD) is an X-linked recessive disease caused by mutations in the dystrophin gene and is characterized by muscle degeneration and death. DMD affects males; females being asymptomatic carriers of mutations. However, some of them manifest symptoms due to a translocation between X chromosome and an autosome or to a heterozygous mutation leading to inactivation of most of their normal X chromosome. Six symptomatic female carriers and two asymptomatic were analyzed by: I) Segregation of STRs-(CA)n and MLPA assays to detect a hemizygous alteration, and II) X chromosome inactivation pattern to uncover the reason for symptoms in these females. The symptomatic females shared mild but progressive muscular weakness and increased serum creatin kinase (CK) levels. Levels of dystrophin protein were below normal or absent in many fibers. Segregation of STRs-(CA)n revealed hemizygous patterns in three patients, which were confirmed by MLPA. In addition, this analysis showed a duplication in another patient. X chromosome inactivation assay revealed a skewed X inactivation pattern in the symptomatic females and a random inactivation pattern in the asymptomatic ones. Our results support the hypothesis that the DMD phenotype in female carriers of a dystrophin mutation has a direct correlation with a skewed X-chromosome inactivation pattern.

Risikoberechnungen beim X-chromosomal rezessiven Erbgang

Am Beispiel der Muskeldystrophie Duchenne werden Risikoberechnungen beim X-chromosomal rezessiven Erbgang mithilfe des Bayesschen Rechentableaus durchgeführt und dabei demonstriert, wie sich auch komplexe genetische Modelle berücksichtigen lassen und auf das Risiko auswirken.

Intragenic DNA polymorphism analysis of DMD/BMD dystrophy gene for carrier and prenatal diagnosis in 60 Iranian healthy individuals

Duchenne and Becker muscular dystrophies (DMD/BMD) are allelic, x-linked neuromuscular disease resulting from mutations in dystrophin gene. DMD is the most severe and frequent inherited but still incurable disease in males. About two-third of such patients have large deletions or duplications that can be identified by multiplex polymerase chain reaction (PCR). In one-third of remaining cases, a linkage analysis that involves DNA markers of intragenic dystrophic gene is considered a rapid and simple method for carrier detection and prenatal diagnosis. In the present study, we investigated frequency and heterozygosity of three polymorphic restriction sites and also four highly polymorphic (CA)(n) repeat microsatellites loci within hot spots region of human dystrophin gene in 60 healthy Iranian populations. Our findings indicated that the allele frequencies of pERT87-8/TaqI, pERT87-15/BamHI, and pERT87-15/XmnI were 0.23/0.77, 0.221/0.779, and 0.239/0.761, respectively. Among these three polymorphic sites, pERT78-15/XmnI locus had the highest heterozygosity with frequency of 47.17%. We also found that STR49 had the highest heterozygosity among four polymorphic microsatellites. These findings are useful in linkage analysis of Iranian DMD families in both carrier detection and prenatal diagnosis.

Muskeldystrophien Duchenne und Becker

Die Duchenne-Muskeldystrophie (DMD) ist die häufigste Muskelerkrankung im Kindesalter. Es liegt ein X-chromosomal rezessiver Erbgang mit Mutationen im Dystrophingen (etwa 65% Deletionen, etwa 7% Duplikationen, etwa 26% Punktmutationen und etwa 2% unbekannte Mutationen) vor. Das genetische Modell ist komplex. Die Mutationsraten in beiden Geschlechtern sind ungleich. Punktmutationen und Duplikationen entstehen eher in der Spermatogenese, Deletionen eher in der Oogenese. Angenähert handelt es sich bezüglich aller Patienten bei etwa 33% um Neumutationen, von welchen der größere Teil als Keimzellmosaik vorliegt. Die Becker-Muskeldystrophie (BMD) ist mit der DMD allelisch.

Modelling Germline Mosaicism and Different New Mutation Rates Simultaneously for Appropriate Risk Calculations in Families with Duchenne Muscular Dystrophy

For several genetic diseases two biological phenomena have been recognised as important: germline mosaicism; and different new mutation rates in males and females depending on mutation type. Both principles have been investigated separately and their influence on risk estimation in families has been exemplified in the literature. The aim of this paper is to present a general model that includes mosaicism and different new mutation rates. Mosaicism is introduced by defining additional alleles at the disease locus in combination with adapted segregation rules. Taking Duchenne muscular dystrophy as an example, we derive the conditions which have to be fulfilled for a population in mutation selection equilibrium. Our approach describes the model at the population level and not in individual subjects. This has the advantage of being able to use well known algorithms for the calculation of likelihoods in pedigrees, and to include additional diagnostic information such as marker genotypes and carrier deletion test results. We demonstrate the impact of the new model on a typical pedigree. In families where the patient is not available, the distinction between point mutations and deletions is important, since often molecular diagnostic tests for females can only screen for deletions. Negative deletion test results can now be included in the risk calculations.

The role of polymorphic short tandem (CA)n repeat loci segregation analysis in the detection of Duchenne muscular dystrophy carriers and prenatal diagnosis

BACKGROUND

Duchenne and Becker muscular dystrophies (DMD/BMD) are X-linked diseases caused by mutations in the dystrophin gene at Xp21.2; they include gross deletions (60%), duplications (10%), and small mutations (30%). Since there is no cure or effective treatment for progressive muscular dystrophy, prevention of the disease is important and strongly depends on carrier-status information. Two-thirds of DMD/BMD cases are familial; thus, female relatives are candidates for carrier-risk assessment.

AIM

Segregation analysis of polymorphic short tandem (CA)n repeats [STR-(CA)n] was used to establish and compare the haplotypes of female relatives of patients with DMD/BMD with those of the patient in order to identify the mutant dystrophin gene and thus determine each female relative's carrier status.

METHODS

248 individuals from 52 families were studied through segregation of up to 11 STR-(CA)n loci. The assay was performed on leukocyte DNA by PCR amplification, polyacrylamide-gel electrophoresis and autoradiography. Haplotypes were established by determination of alleles on the autoradiography.

RESULTS

38 of 51 (75%) female relatives from familial cases were diagnosed as carriers or non-carriers with a 95-100% likelihood, and 18 out of 56 (32%) female relatives from sporadic cases could be excluded from the risk of being a DMD carrier with the same probability. In addition, STR studies detected gross deletions in 13 of the 52 (25%) families in both male and female individuals, four of which were de novo deletions. STR assays were also informative in families without an available DNA sample of an affected male and in two of seven symptomatic females. Determination of carrier status was particularly significant for prediction of DMD risk in prenatal analysis of five male chorionic villi. Other genetic events revealed by STR analysis were: (i) 11 recombinations identified in 6.6% of meiosis in the DMD families; (ii) germinal mosaicism detected in two female carriers; and (iii) changes in STR-(CA)n length during transmission from father to daughters, including three retractions and one elongation at an estimated rate of 0.004.

CONCLUSION

The STR assay is an excellent molecular tool for carrier-status identification and the detection of deletions and other genetic changes in families affected by DMD/BMD. Thus, it is useful in genetic counseling for the prevention of this disease.

Detection of germline mosaicism in two Duchenne muscular dystrophy families using polymorphic dinucleotide (CA)n repeat loci within the dystrophin gene

BACKGROUND

Approximately one-third of new cases of Duchenne muscular dystrophy (DMD) can be attributed to sporadically arising new mutations, however in the majority of cases the DMD mutation has been inherited from the mother. These female carriers can have either a constitutive or mosaic mutation.

AIM

The aim of this study was to determine the segregation of the at-risk haplotype and to find a deletion in the dystrophin gene of patients.

METHOD

We analyzed individuals from two families with a history of DMD in order to predict the carrier status of related females. In one of these cases the mother had two affected sons, while in the other one son and two grandchildren were affected; therefore we predict that the mother would be an obligatory carrier.

RESULTS

Haplotype analysis of the DMD loci revealed that in the two families both the healthy and affected brothers had inherited the same X maternal chromosome. However, the affected brother carried a deletion, which was absent in the unaffected sibling.

CONCLUSION

These findings suggested that the mothers in the two families were germline mosaics for the DMD gene. The results of this study demonstrate the usefulness of the methodology that combine the haplotype analysis with the identification of the mutation in order to detect hidden germline mosaicisms and, thus, improve genetic counseling.

Genetic diseases of muscle

In the last twenty years, the genetic basis for most of the inherited myopathies and muscular dystrophies has been unveiled. Diseases have been found to result from loss of function of structural components of the muscle basal lamina (e.g., MCD1A), sarcolemma (e.g., the sarcoglycanopathies), nucleus (e.g., EDMD) and sarcomere (e.g., the nemaline myopathies). A few have been associated with abnormalities in the genes for muscle enzymes (e.g., calpain and fukutin). Alternate mechanisms of pathogenesis have also recently been suggested by mutations lying outside of coding regions, such as the "field effect" of chromosomal mutations in DM2. In the future, we will likely identify the genes responsible for the remaining disorders, including many of the distal myopathies. In addition, we may also find skeletal muscle diseases associated with some of the presently non-implicated muscle proteins: syntropin, dystrobrevin, epsilon-sarcoglycan and sarcospan. The next steps may be to identify and understand the relationship of modifier genes producing the phenotypic heterogeneity of many of these diseases and to characterize those and other targets for therapeutic intervention, whether by gene therapy or by pharmacological treatment.

Brain function in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is the second most commonly occurring genetically inherited disease in humans. It is an X-linked condition that affects approximately one in 3300 live male births. It is caused by the absence or disruption of the protein dystrophin, which is found in a variety of tissues, most notably skeletal muscle and neurones in particular regions of the CNS. Clinically DMD is characterized by a severe pathology of the skeletal musculature that results in the premature death of the individual. An important aspect of DMD that has received less attention is the role played by the absence or disruption of dystrophin on CNS function. In this review we concentrate on insights into this role gained from investigation of boys with DMD and the genetically most relevant animal model of DMD, the dystrophin-deficient mdx mouse. Behavioural studies have shown that DMD boys have a cognitive impairment and a lower IQ (average 85), whilst the mdx mice display an impairment in passive avoidance reflex and in short-term memory. In DMD boys, there is evidence of disordered CNS architecture, abnormalities in dendrites and loss of neurones, all associated with neurones that normally express dystrophin. In the mdx mouse, there have been reports of a 50% decrease in neurone number and neural shrinkage in regions of the cerebral cortex and brainstem. Histological evidence shows that the density of GABA(A) channel clusters is reduced in mdx Purkinje cells and hippocampal CA1 neurones. At the biochemical level, in DMD boys the bioenergetics of the CNS is abnormal and there is an increase in the levels of choline-containing compounds, indicative of CNS pathology. The mdx mice also display abnormal bioenergetics, with an increased level of inorganic phosphate and increased levels of choline-containing compounds. Functionally, DMD boys have EEG abnormalities and there is some preliminary evidence that synaptic function is affected adversely by the absence of dystrophin. Electrophysiological studies of mdx mice have shown that hippocampal neurones have an increased susceptibility to hypoxia. These recent findings on the role of dystrophin in the CNS have implications for the clinical management of boys with DMD.

Genetic, biochemical, and clinical features of chronic granulomatous disease

The reduced nicotinamide dinucleotide phosphate (NADPH) oxidase complex allows phagocytes to rapidly convert O2 to superoxide anion which then generates other antimicrobial reactive oxygen intermediates, such as H2O2, hydroxyl anion, and peroxynitrite anion. Chronic granulomatous disease (CGD) results from a defect in any of the 4 subunits of the NADPH oxidase and is characterized by recurrent life-threatening bacterial and fungal infections and abnormal tissue granuloma formation. Activation of the NADPH oxidase requires translocation of the cytosolic subunits p47phox (phagocyte oxidase), p67phox, and the low molecular weight GT-Pase Rac, to the membrane-bound flavocytochrome, a heterodimer composed of the heavy chain gp91phox and the light chain p22phox. This complex transfers electrons from NADPH on the cytoplasmic side to O2 on the vacuolar or extracellular side, thereby generating superoxide anion. Activation of the NADPH oxidase requires complex rearrangements between the protein subunits, which are in part mediated by noncovalent binding between src-homology 3 domains (SH3 domains) and proline-rich motifs. Outpatient management of CGD patients relies on the use of prophylactic antibiotics and interferon-gamma. When infection is suspected, aggressive effort to obtain culture material is required. Treatment of infections involves prolonged use of systemic antibiotics, surgical debridement when feasible, and, in severe infections, use of granulocyte transfusions. Mouse knockout models of CGD have been created in which to examine aspects of pathophysiology and therapy. Gene therapy and bone marrow transplantation trials in CGD patients are ongoing and show great promise.

Carrier detection in Duchenne and Becker muscular dystrophy Argentine families

In order to offer carrier detection, genetic counseling, and prenatal diagnosis to families with Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) in our country, segregation analysis of highly polymorphic short tandem repeats (STR) (dC-dA)n: (dG-dT)n loci was utilized. The risks to females of 15 DMD BMD families (9 familial and 6 sporadic) were evaluated on STR, pedigree and serum creatine kinase (SCK) data. From the 36 females at risk of being carriers (not including 8 obligate carriers), results of STR analysis were compatible with carrier status in 7 and not compatible in 20. In 9 females, no information regarding carriership was derived from the STR analysis. Prenatal diagnosis is now possible on the carrier females. Previously identified deletions in the central part of the gene were confirmed by STR analysis in 3 families. Five new alleles were identified in Argentine individuals; allele frequencies differed from those of North American people. Results derived from this study are useful for carrier detection and genetic counseling in DMD/BMD. One case of probable mosaicism in an unaffected father was detected on a pedigree basis in a family with DMD patients.

Genetic analysis of 13 families with X-linked chronic granulomatous disease reveals a low proportion of sporadic patients and a high proportion of sporadic carriers

X-linked chronic granulomatous disease (X-CGD) is the most common type of CGD, whose responsible gene has been identified and termed as CYBB, according to the gp91-phox, a subunit of cytochrome b558. Although approximately 200 different mutations of the gp91-phox gene have been reported, no precise study of the proportion of sporadic cases in X-CGD, based on molecular genetic analysis, has been reported. We made a genetic analysis of six newly identified X-CGD patients together with that of eight previously reported X-CGD patients. The mutations newly detected were three missense mutations, two splice mutations, and one insertion of 2 bases. All of the mutations were novel. Twelve mothers (two of them came from the same family) and four maternal grandmothers from 13 different X-CGD families were available for further genetic studies. It was revealed that a proportion of sporadic patients was low and that of sporadic carriers was high. These results suggest that the mutation for the disease originates mainly from male gametes.

Molecular genetic analysis of 67 patients with Duchenne/Becker muscular dystrophy

A total of 56 Duchenne muscular dystrophy (DMD) patients and 11 Becker muscular dystrophy (BMD) patients was analyzed by extended "multiplex" amplification of the DMD/BMD gene; deletions were found in 60% of these patients. The data obtained were used to test the frameshift hypothesis and to compare the distribution of familial versus isolated cases. A significant correlation was found between deletions and isolated cases. Additional experiments were performed in order to determine the deletion breakpoints more precisely. These data are a prerequisite for carrier analysis in the respective families by detection or exclusion of aberrant cDNA fragments derived from ectopic lymphocyte RNA. This diagnostic technique is illustrated by 5 examples.

Similar proportion of sporadic cases in cytochrome b558 negative chronic granulomatous disease and Duchenne muscular dystrophy

We studied 12 Japanese families of cytochrome b558 (b) negative chronic granulomatous disease (13 patients and 23 family members) and 15 controls for cytochrome b content, O2-, and H2O2 production. Cytochrome b content (nmol/10(8) cells), O2- production (nmol/10(7) cells/min), and percentage of H2O2 generating cells (%) were 1) 0.45-1.19, 64.1-174.2, and 85.8-100.0 in controls (mean +/- 2 S.D.), 2) 0.13-0.38, 22.6-50.9, and 20.0-62.4 in healthy carriers, and 3) undetectable, undetectable, and 0 in patients, respectively. These findings indicate that healthy carriers and normal homozygotes are separable by these three parameters, and that 4 of the 12 families studied represent fresh gene mutation. Pooling of data by Segal et al., Ohno et al., and ours yielded the overall incidence of a fresh gene mutation to be 19.4% (7 of 36 cases). The lower fresh mutation rate than predicted from Haldane's formula suggests a higher mutation rate in males than in females, as previously suggested in Duchenne muscular dystrophy.

Genetic epidemiology of complex phenotypes

A theory is given for complex phenotypes represented by an ordered polychotomy separately for affected (as severity) and for normals (as diathesis), with consideration of history, ascertainment, sampling frames, and phenotype systems. Nonrandom selection of probands by severity is permitted. Both probit and logistic models are developed in a form compatible with segregation and/or linkage analysis. Probabilities are set out in detail in the Appendix. This approach avoids problems that have been encountered with quantitative traits and correlated phenotypes, although using this information.

Theoretical considerations on germline mosaicism in Duchenne muscular dystrophy

A newly formulated mutation selection equilibrium for lethal X linked recessive traits such as Duchenne muscular dystrophy is presented, which allows for both male and female germline mosaicism. Estimates of the additional parameters used are given, thus allowing the incorporation of germline mosaicism into the calculation of genetic risks.