Possible influences on the expression of X chromosome-linked dystrophin abnormalities by heterozygosity for autosomal recessive Fukuyama congenital muscular dystrophy

The genetic basis of hydrocephalus: genes, pathways, mechanisms, and global impact

Hydrocephalus (HC) is a heterogenous disease characterized by alterations in cerebrospinal fluid (CSF) dynamics that may cause increased intracranial pressure. HC is a component of a wide array of genetic syndromes as well as a secondary consequence of brain injury (intraventricular hemorrhage (IVH), infection, etc.) that can present across the age spectrum, highlighting the phenotypic heterogeneity of the disease. Surgical treatments include ventricular shunting and endoscopic third ventriculostomy with or without choroid plexus cauterization, both of which are prone to failure, and no effective pharmacologic treatments for HC have been developed. Thus, there is an urgent need to understand the genetic architecture and molecular pathogenesis of HC. Without this knowledge, the development of preventive, diagnostic, and therapeutic measures is impeded. However, the genetics of HC is extraordinarily complex, based on studies of varying size, scope, and rigor. This review serves to provide a comprehensive overview of genes, pathways, mechanisms, and global impact of genetics contributing to all etiologies of HC in humans.

Duchenne Muscular Dystrophy and Early Onset Hypertrophic Cardiomyopathy associated with Mutations in Dystrophin and Hypertrophic Cardiomyopathy-Associated Genes

Duchenne muscular dystrophy (DMD) is a progressive muscular damage disorder caused by mutations in dystrophin gene. Cardiomyopathy may first be evident after 10 years of age and increases in incidence with age. We present a boy diagnosed at 18 months with a rare phenotype of DMD in association with early-onset hypertrophic cardiomyopathy (HCM). The cause of DMD is a deletion of exons 51–54 of dystrophin gene. The cause of HCM was verified by whole exome sequencing. Novel missense variations in two genes: MAP2K5 inherited from the mother and ACTN2 inherited from the father, or de novo. The combination of MAP2K5, ACTN2, and dystrophin mutations, could be causing the HCM in our patient. This is the second patient diagnosed, at relatively young age, with DMD and HCM, with novel variations in genes known to cause HCM. This study demonstrates the need for genetic diagnosis to elucidate the underlying pathology of HCM.

From genotype to phenotype: genetics and medical practice in the new millennium

The completion of the human genome project will provide a vast amount of information about human genetic diversity. One of the major challenges for the medical sciences will be to relate genotype to phenotype. Over recent years considerable progress has been made in relating the molecular pathology of monogenic diseases to the associated clinical phenotypes. Studies of the inherited disorders of haemoglobin, notably the thalassaemias, have shown how even in these, the simplest of monogenic diseases, there is remarkable complexity with respect to their phenotypic expression. Although studies of other monogenic diseases are less far advanced, it is clear that the same level of complexity will exist. This information provides some indication of the difficulties that will be met when trying to define the genes that are involved in common multigenic disorders and, in particular, in trying to relate disease phenotypes to the complex interactions between many genes and multiple environmental factors.

Rett syndrome and genetic drift

An X chromosome gene is assumed to be responsible for the cause of Rett syndrome (RS). However, new genealogical observations suggest involvement of autosomal recessive gene(s) as well, at least in familial cases. To account for these and other recent observations, the theoretical model presented in 1990 by the authors of this paper is applied to the calculation of gene frequencies. Observed frequencies of sporadic and familial cases of RS are used, taking into account genetic drift in inbreeded areas. Moreover, an attempt is made to use the proportion of RS variants in familial and sporadic cases for the explanation of so called 'formes frustes', and as evidence for the existence of female as well as male carriers. The estimated frequency of the recessive autosome mutation, or possibly a frequent polymorphism, is 22.5%.

Severe dystrophinopathy in a patient with congenital hypotonia

We studied a 2-year-old child with congenital hypotonia and proximal muscle weakness. There was no family history of neuromuscular disease. The child also had hypospadia. The central nervous system was apparently not involved. Muscle biopsy showed a dystrophic pattern and dystrophin was absent as shown by immunofluorescence and by Western blot. Vinculin and spectrin were also reduced, while merosin was normal in muscle fibers. This observation suggests that congenital hypotonia may be associated with a severe form of dystrophinopathy.

Immunohistochemical alterations of dystrophin in congenital muscular dystrophy

The dystrophin distribution in the plasma muscle membrane using immunohystochemistry was studied in 22 children with congenital muscular dystrophy. The dystrophin was detected by immunofluorescence in muscle biopsy through a polyclonal antibody. All the cases had patchy interruptions of the fluorescence in the plasma membrane. A large patchy interruption of the sarcolemma was found in 17 cases, small interruption in 12, and a combination of large and small patchy discontinuity in 7. Small gaps around the fiber like a rosary were found in 15 cases. The frequency of these abnormalities ranged cases from: all fibers in 5 cases, frequent in 8, occasional in 5, and rare in 4. Five cases had total absence of immunofluorescence. These results suggest that the dystrophin expression is abnormal in this group of children and that this type of abnormalities can not be differentiated from early Becker muscular dystrophy nor childhood autosomal recessive muscular dystrophy through immunohystochemistry alone.

X-chromosome methylation in manifesting and healthy carriers of dystrophinopathies: concordance of activation ratios among first degree female relatives and skewed inactivation as cause of the affected phenotypes

The X-chromosome activity states of 11 manifesting carriers of dystrophinopathies, all with normal karyotypes, were estimated by restriction fragment length polymorphism (RFLP)-methylation analysis with the probes M27 beta (DXS255), p2-19(DXS605) and pSPT/PGK (PGK1) to test the role of skewed X-inactivation ratios as the cause of their affected phenotypes. In eight cases preferential inactivation of the putative X chromosome carrying the normal dystrophin allele in > or = 90% of their peripheral lymphocytes was observed, two cases showed non-apparent deviant ratios (60:40 and 70:30) from the theoretically expected values around the mean of 50% and in one case the three markers employed yielded no information. The analysis of the X-inactivation ratio in six mother-daughter pairs, all non-manifesting Duchenne muscular dystrophy (DMD) carriers, and in the close female relatives of the patients showed: (a) neither of the two X chromosomes was preferentially inactivated with respect to their parental origin; (b) a high concordance among the activation ratios of mothers and daughters, a result difficult to explain just in terms of random X-chromosome inactivation.

Three-dimensional MR imaging of brain surface anomalies in Fukuyama-type congenital muscular dystrophy

Fukuyama-type congenital muscular dystrophy (FCMD), the second most common childhood muscular dystrophy in Japan, is characterized by the association with severe brain anomalies such as pachygyria and focal interhemispheric fusion. Conventional imaging techniques such as X-ray CT scan and MRI are ineffective for visualization of these brain surface anomalies. Here we investigated the efficacy of three-dimensional (3-D) reconstruction of brain surface MR images for the detection of brain anomalies in FCMD patients. 3-D brain surface MR images clearly visualized anomalies of cerebral gyrus such as pachygyria, as well as focal interhemispheric fusion. In addition, reconstructed horizontal images visualized structural derangement such as abnormal protrusion of white matter into gray matter. MR image abnormalities were confirmed by autopsy in 1 patient. These abnormalities were never observed in Duchenne muscular dystrophy (DMD) patients. Our results indicate the efficacy of the present method for the differential diagnosis between FCMD and DMD with severe mental retardation, which is essential for the genetic study to identify the causative gene of FCMD.

The molecular basis of genetic dominance

Studies of mutagenesis in many organisms indicate that the majority (over 90%) of mutations are recessive to wild type. If recessiveness represents the 'default' state, what are the distinguishing features that make a minority of mutations give rise to dominant or semidominant characters? This review draws on the rapid expansion in knowledge of molecular and cellular biology to classify the molecular mechanisms of dominant mutation. The categories discussed include (1) reduced gene dosage, expression, or protein activity (haploinsufficiency); (2) increased gene dosage; (3) ectopic or temporally altered mRNA expression; (4) increased or constitutive protein activity; (5) dominant negative effects; (6) altered structural proteins; (7) toxic protein alterations; and (8) new protein functions. This provides a framework for understanding the basis of dominant genetic phenomena in humans and other organisms.

Dystrophin-glycoprotein complex: its role in the molecular pathogenesis of muscular dystrophies

Dystrophin, the protein product of the Duchenne muscular dystrophy (DMD) gene, is associated with a large oligomeric complex of sarcolemmal glycoproteins, including dystroglycan which provides a linkage to the extracellular matrix component, laminin. In patients with DMD, the absence of dystrophin leads to the loss in all of the dystrophin-associated proteins, causing the disruption of the linkage between the subsarcolemmal cytoskeleton and the extracellular matrix. This may render the sarcolemma vulnerable to physical stress. These recent developments in the research concerning the function of the dystrophin-glycoprotein complex pave a way for the better understanding of the pathogenesis of muscular dystrophies.

Localization of a gene for Fukuyama type congenital muscular dystrophy to chromosome 9q31-33

Fukuyama type congenital muscular dystrophy (FCMD) is an autosomal recessive severe muscular dystrophy associated with an anomaly of the brain. Twenty-one FCMD families, 13 of them with consanguineous marriages, were analysed by genetic linkage analyses with polymorphic microsatellite markers to map the FCMD gene. Significant lod scores were obtained with the markers D9S58 (Zmax = 5.81 at theta = 0.06), D9S59 (Zmax = 4.33 at theta = 0.02), and HXB (Zmax = 3.28 at theta = 0.09) on chromosome 9q31-33. Multipoint analysis placed FCMD between D9S58 and D9S59, with a maximum lod score of 16.93. These markers will be useful for presymptomatic, prenatal and carrier diagnosis of family members carrying FCMD, and they represent important resources for the identification of a gene responsible for FCMD.

Integrated study of 100 patients with Xp21 linked muscular dystrophy using clinical, genetic, immunochemical, and histopathological data. Part 3. Differential diagnosis and prognosis

This report is the third part of a trilogy from a multidisciplinary study which was undertaken to investigate gene and protein expression in a large cohort of patients with well defined and diverse clinical phenotypes. The aim of part 3 was to review which of the analytical techniques that we had used would be the most useful for differential diagnosis, and which would provide the most accurate indication of disease severity. Careful clinical appraisal is very important and every DMD patient was correctly diagnosed on this basis. In contrast, half of the sporadic BMD patients and all of the sporadic female patients had received different tentative diagnoses based on clinical assessments alone. Sequential observations of quantitative parameters (such as the time taken to run a fixed distance) were found to be useful clinical indicators for prognosis. Intellectual problems might modify the impression of physical ability in patients presenting at a young age. Histopathological assessment was accurate for DMD but differentiation between BMD and other disorders was more difficult, as was the identification of manifesting carriers. Our data on a small number of women with symptoms of muscle disease indicate that abnormal patterns of dystrophin labelling on sections may be an effective way of differentiating between female patients with a form of limb girdle dystrophy and those carrying a defective Xp21 gene. Dystrophin gene analysis detects deletions/duplications in 50 to 90% of male patients and is the most effective non-invasive technique for diagnosis. Quantitative Western blotting, however, would differentiate between all Xp21 and non-Xp21 male patients. In this study we found a clear relationship between increased dystrophin abundance (determined by densitometric analysis of blots) and clinical condition, with a correlation between dystrophin abundance and the age at loss of independent mobility among boys with DMD and intermediate D/BMD. This indicates that blotting is the most sensitive and accurate technique for diagnosis and prognosis.

The structural and functional diversity of dystrophin

Duchenne and Becker muscular dystrophies are caused by defects of the dystrophin gene. Expression of this large X-linked gene is under elaborate transcriptional and splicing control. At least five independent promoters specify the transcription of their respective alternative first exons in a cell-specific and developmentally controlled manner. Three promoters express full-length dystrophin, while two promoters near the C terminus express the last domains in a mutually exclusive manner. Six exons of the C terminus are alternatively spliced, giving rise to several alternative forms. Genetic, biochemical and anatomical studies of dystrophin suggest that a number of distinct functions are subserved by its great structural diversity. Extensive studies of dystrophin may lead to an understanding of the cause and perhaps a rational treatment for muscular dystrophy.

Abnormal expression of dystrophin-associated proteins in Fukuyama-type congenital muscular dystrophy

The absence of dystrophin causes Duchenne muscular dystrophy. Dystrophin is associated with a large complex of sarcolemmal glycoproteins which provides a linkage to the extracellular matrix component, laminin, and when dystrophin is absent all the dystrophin-associated proteins are much reduced. We report here that dystrophin-associated proteins have abnormally low expression in Fukuyama-type congenital muscular dystrophy (FCMD), despite near-normal expression of dystrophin. An abnormality of dystrophin-associated proteins in the sarcolemma seems to be a common denominator in the pathological processes leading to muscle cell necrosis in three forms of severe muscular dystrophy (Duchenne, Japanese Fukuyama-type, and north African Duchenne-like autosomal recessive).

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.

The first decade of molecular genetics in neurology: changing clinical thought and practice

Molecular genetics has had a powerful impact on clinical neurology. Definitions of disease are changing from clinical criteria to DNA analysis, resolving questions about the nature of clinically similar but not identical diseases. Genetic counseling is more reliable. Concepts of mendelian inheritance are being tested and new forms of mutation have been discovered to explain anticipation. Nonmendelian forms of inheritance have emerged; concepts of pathogenesis are on a more secure footing; and novel treatments are being explored.