Prenatal diagnosis of Fukuyama type congenital muscular dystrophy by polymorphism analysis

Prenatal diagnosis of muscle-eye-brain disease

OBJECTIVES

To present a family in which it was possible to perform prenatal diagnosis for the recessively inherited muscle-eye-brain disease (MEB) using linkage analysis.

METHODS

Linkage analysis and direct sequencing of the POMGNT1 gene were carried out in a Turkish MEB family with one affected individual. Fetal DNA was obtained from an ongoing pregnancy by chorionic villus sampling (CVS).

RESULTS

Both linkage analysis of the POMGNT1/1p32-p34 region and direct sequencing for the novel familial mutation (R605H) demonstrated that the fetus did not have MEB.

CONCLUSION

We report the first case of prenatal diagnosis in MEB by molecular genetic analysis.

Prenatal diagnosis of Fukuyama congenital muscular dystrophy

Fukuyama congenital muscular dystrophy (FCMD) is characterized by infantile hypotonia, symmetrical generalized muscle weakness, and neuronal migration disturbances that result in changes consistent with cobblestone lissencephaly with cerebral and cerebellar cortical dysplasia. FCMD is recognized as an autosomal recessive genetic defect. Genetic counselling is recommended for parents at risk of having a child with FCMD. Given the high risk and overwhelming prospect of having another child with this incurable devastating condition leads many couples to consider prenatal diagnosis. In Japanese families, haplotype analysis using microsatellite markers is available. In non-Japanese families, DNA sequence analysis is available. Both disease-causing alleles of an affected family member must be identified before prenatal testing can be performed.

A case of Walker-Warburg syndrome

Walker-Warburg syndrome (WWS) is an autosomal recessive disorder characterized by type II lissencephaly, cerebellar and retinal anomalies, and congenital muscular dystrophy. We report a female diagnosed with WWS based on clinical criteria. This patient was found to have fetal hydrocephalus on ultrasonography at 29 weeks of gestation, and exhibited severe hypotonia, ocular malformations, and hydrocephalus at birth. MRI revealed type II lissencephaly, hydrocephalus, and other severe brain malformations. Genetic analysis was performed to distinguish WWS from severe Fukuyama-type congenital muscular dystrophy (FCMD), which has numerous findings in common. This revealed no expression of the founder haplotype or single-stranded conformation polymorphism (SSCP) abnormalities. Since the life expectancy of patients with FCMD is longer, differential diagnosis should be performed precisely.

The Fukuyama congenital muscular dystrophy story

Fukuyama congenital muscular dystrophy is one of the most common autosomal recessive disorders in the Japanese population, characterized by congenital muscular dystrophy in combination with cortical dysgenesis (micropolygyria). Recently, we have identified the gene responsible for fukuyama congenital muscular dystrophy on 9q31, which encodes a novel 461-amino-acid protein termed fukutin. Most Fukuyama congenital muscular dystrophy-bearing chromosomes are derived from a single ancestral founder (87%), and a 3 kb-retrotransposal insertion into the 3' untranslated region of this gene was found to be a founder mutation. Two independent point mutations causing premature termination confirmed that that this gene is responsible for Fukuyama congenital muscular dystrophy. Fukuyama congenital muscular dystrophy is the first human disease to be caused by an ancient retrotransposal integration. Fukutin contains an amino-terminal signal sequence, which together with results from transfection experiments suggests that it is an extracellular protein. Discovery of the Fukuyama congenital muscular dystrophy gene represents an important step toward greater understanding of the pathogenesis of muscular dystrophies and also of normal brain development.

Early ultrastructural changes in the central nervous system in Fukuyama congenital muscular dystrophy

Electron microscopy of the central nervous system surface structure is described in two fetuses with Fukuyama congenital muscular dystrophy (FCMD). In addition to relatively large surface defects, many minute defects less than several micrometers in size associated with protrusion of glial cytoplasm were observed in the cerebrum. These findings were considered to represent early changes prior to cortical dysplasia. The basement membrane adjacent to the defects showed amorphous, wavy, or whorled configurations, and gradually disappeared. The glial cytoplasmic membrane seemed to be relatively well preserved in some areas where the basement membrane disappeared. On the other hand, both the basement membrane and cytoplasmic membrane became indistinct irregularly in areas without defects, including the spinal cord; similar lesions were found in the skeletal muscle. These observations confirm previous observations concerning defects of the pial-glial barrier of the brain surface, and may suggest the involvement of abnormal basement membrane or related structures, or both, in the genesis of the brain lesions of FCMD.

Polymorphism analysis of Fukuyama type congenital muscular dystrophy (FCMD) siblings with different phenotypes

Peak motor function in Fukuyama type congenital muscular dystrophy (FCMD) is generally considered to be no better than sitting without help or sliding on the buttocks. There are a few patients who acquire the ability to stand and a small fraction of our total congenital muscular dystrophy (CMD) population are able to walk at some point. These ambulant cases may reflect a broad spectrum of motor disabilities in the category of FCMD, or may represent another CMD entity, which closely resembles but is distinct from FCMD. Since the localization of the FCMD gene to chromosome 9q3 1 by Toda et al. in 1993 and 1994, polymorphism analysis of this disease has become possible. We describe correlations between clinical features and genetic analysis using microsatellite markers flanking the FCMD locus in two FCMD families each having two affected children with distinctly different motor abilities. The results demonstrate that two sets of FCMD siblings share exactly the same haplotype at nine marker loci spanning 23.3 cM, surrounding the FCMD locus. Our results provide genetic confirmation that some FCMD cases may acquire the ability to walk.

Pial-glial barrier abnormalities in fetuses with Fukuyama congenital muscular dystrophy

This report concerns light and electron microscopic studies on the central nervous system of a 20-week and an 18-week fetus with Fukuyama congenital muscular dystrophy (FCMD). The diagnosis of FCMD was established by prenatal molecular genetic analysis. Cerebral lesions containing neurites, subpial granular cells and glias, accompanied by cortical dysplasia were found in both cases. Small irregular defects, readily detectable by periodic acid-methenamine-silver staining or by immunohistochemical staining for S-100 protein, were observed in the cerebral surface. More severe dysplasia was evident at the areas with the larger defects. Surface defects were also observed in the cerebellum and brain stem, with brain tissue extruding into the leptomeninges. The pyramidal tract was aberrant in the pons and medulla oblongata. The spinal cord appeared normal by light microscopy. Electron microscopic examination revealed an abnormal configuration of the basement membrane and glial cytoplasmic membrane of the brain and spinal cord surfaces, including areas with no detectable defects by light microscopy. These findings suggest that abnormalities of the pial-glial barrier, especially the basement membrane and/or basement membrane-related structures, are involved in the genesis of cortical dysplasia.