Ocular manifestations in Fukuyama type congenital muscular dystrophy

Congenital muscular dystrophies and the extracellular matrix

During the past decade, considerable progress in the field of congenital muscular dystrophies (CMDs) had led to the identification of a growing number of causative genes. This genetic progress has uncovered crucial pathophysiological concepts and has been instrumental in redefining clinical phenotypes. Important new pathogenic mechanisms include the disorders of O-mannosyl-linked glycosylation of alpha-dystroglycan as well as the involvement of a collagen type VI in the pathogenesis of congenital disorders of muscle. Thus, an emerging theme among gene products involved in the pathogenesis of congenital muscular dystrophy is their intimate connection to the extracellular matrix. In this review, we focus on the clinical phenotypes that we are correlating with the novel genetic and biochemical findings encountered within CMD. This correlation will frequently lead to a considerably expanded clinical spectrum associated with a given CMD gene.

The congenital muscular dystrophies: recent advances and molecular insights

Over the past decade, molecular understanding of the congenital muscular dystrophies (CMDs) has greatly expanded. The diseases can be classified into 3 major groups based on the affected genes and the location of their expressed protein: abnormalities of extracellular matrix proteins (LAMA2, COL6A1, COL6A2, COL6A3), abnormalities of membrane receptors for the extracellular matrix (fukutin, POMGnT1, POMT1, POMT2, FKRP, LARGE, and ITGA7), and abnormal endoplasmic reticulum protein (SEPN1). The diseases begin in the perinatal period or shortly thereafter. A specific diagnosis can be challenging because the muscle pathology is usually not distinctive. Immunostaining of muscle using a battery of antibodies can help define a disorder that will need confirmation by gene testing. In muscle diseases with overlapping pathological features, such as CMD, careful attention to the clinical clues (e.g., family history, central nervous system features) can help guide the battery of immunostains necessary to target an unequivocal diagnosis.

Congenital muscular dystrophies

The number of new syndromes, loci, and genes responsible for CMD forms has dramatically increased in the last few years, and it has become increasingly evident that the classification of the different forms of CMD is a difficult task. A recent classification separated the forms of CMD that have been mapped (CMD diseases) from the ones with clearly defined clinical and pathologic features that have not been mapped yet (CMD syndromes). Eight CMD forms have been mapped up to now, and the genes responsible for three of them have been identified. This review describes an update of clinical, pathologic, and genetic findings in the different CMD forms.

Clinicopathological study on eyes from cases of Fukuyama type congenital muscular dystrophy

Fukuyama type congenital muscular dystrophy (FCMD) is an autosomal recessive disorder characterized by progressive muscular dystrophy and dysgenesis of the central nervous system and eyes. To clarify the pathomechanism of the ocular involvement in FCMD, we performed postmortem pathological analyses of eyes from three postnatal FCMD cases, two fetal FCMD cases, and three control cases by macroscopic, histopathological, immunohistochemical and in situ hybridization approaches. The macroscopic and histopathological examinations revealed a variety of ocular abnormalities such as folding, fusion or dysplasia of the retinas in the FCMD cases both with and without ophthalmological alterations. Immunoreactivities for collagen IV and laminin, produced by Müller cells, as the basement membrane components, were less intense in the inner limiting membrane of the FCMD retinas than in that of the control retinas. A number of the perivascular glial cells containing S-100 protein and glial fibrillary acidic protein were increased in the postnatal FCMD cases. Immunoreactivities for vimentin, glutamate transporter-1, glutamine synthase and ornithine aminotransferase, expressed in the Müller cells, were undetectable in the fetal FCMD retinas, and reduced in the postnatal FCMD retinas compared with the control retinas. Fukutin mRNA signals were distributed diffusely in the retinoblast layer of the control retinas, focally in the retinoblast layer of the fetal FCMD retinas, and only in the dysplastic areas with rosette formation of the postnatal FCMD retinas, composed of retinoblasts and other retinal cells including the Müller cells. The present findings suggest that the Müller cells are implicated in the retinal pathology of FCMD.

Immature astrocytes in Fukuyama congenital muscular dystrophy: an immunohistochemical study

Recent studies of Fukuyama congenital muscular dystrophy have focused on abnormalities of the basement membrane in muscle and brain. The cerebral cortex has a unique basement membrane at the glia limitans, which is intimately related to astrocytes in the developing brain, and the basement membrane may be partially produced by the astrocyte. In this study the cerebral astrocytes in six patients with Fukuyama congenital muscular dystrophy, including two fetal patients, were characterized by immunohistochemical study. In fetal Fukuyama congenital muscular dystrophy, astrocytes reacted less to antibodies of glial fibrillary acidic protein, S-100 protein, and alphaB-crystallin than control astrocytes, but in postnatal Fukuyama congenital muscular dystrophy, astrocytes reacted more to these antibodies and displayed beading of processes. Moreover, vimentin was positive in the astrocytes of two postnatal Fukuyama congenital muscular dystrophy patients. This astrocytic appearance may suggest immaturity of astrocytes in Fukuyama congenital muscular dystrophy. Astrocytes exhibiting beaded cytoplasmic processes were prominent at the subpia of the cortex and around vessels. The authors hypothesize that these immature astrocytes are unable to participate in the function of the cortical basement membrane, which is defective in Fukuyama congenital muscular dystrophy. Studies of neurons and meninges were similar to those of control subjects.

Muscle-eye-brain disease: a neuropathological study

A combination of congenital central nervous, ocular and muscular abnormalities is characteristic of muscle-eye-brain disease (MEB), of Fukuyama congenital muscular dystrophy (FCMD), and of Walker-Warburg syndrome (WWS). The nosological relationship of these inherited malformative disorders is still unestablished, although the genetic locus for FCMD has been excluded in MEB. We present the first postmortem neuropathological study of MEB based on 2 male patients. Apart from sharply limited occipital agyric areas, their brains showed coarse gyri with an abnormally nodular surface ("cobblestone cortex"). Both the cerebral and cerebellar cortices showed a total disorganization without horizontal lamination. The haphazardly oriented cortical neurons formed irregular clusters or islands, separated by gliovascular strands extending from the pia. The ocular abnormalities included a pronounced glial preretinal membrane. Although MEB shares the cobblestone cortex-type malformation with FCMD and WWS, the cerebral and ocular manifestations are less severe than in WWS. Furthermore, a consistently weak staining for laminin alpha2 chain (merosin) was found in muscle biopsy specimens from 4 MEB patients, while normal immunoreactivity was observed for the laminin beta2 chain, reported to be severely deficient in WWS. These findings support nosological independence of MEB.

Muscle-eye-brain disease and Fukuyama type congenital muscular dystrophy are not allelic

Muscle-Eye-Brain disease (MEB) and Fukuyama type congenital muscular dystrophy (FCMD) are clinically similar autosomal recessive diseases, characterized by congenital muscular dystrophy and severe mental retardation, raising the possibility that they might be caused by mutations of the same gene. Recently FCMD was localized to chromosome 9q31-33 by linkage. We performed a linkage study in seven Finnish MEB families with 12 affected patients using markers D9S53, D9S58, D9S59 and HXB. The MEB phenotype was not linked to any of the markers. A multipoint linkage analysis excluded the entire region harboring FCMD. We thus conclude that MEB and FCMD are not allelic.

Ocular findings in muscle-eye-brain (MEB) disease: a follow-up study

We present ocular findings of 20 patients with the recessively inherited muscle-eye-brain (MEB) disease, characterised by severe visual failure, mental retardation, a pachygyria-polymicrogyria type neuronal migration disorder and congenital muscular dystrophy. The ocular findings consisted of myopia ranging from -6 to -27 D, retinal degeneration and optic atrophy. Five infants had congenital glaucoma, and juvenile cataracts developed in 9 children. The visual evoked potentials were abnormally high (> 50 microV) and delayed in 70% of patients. The electroretinogram was abolished in 12 patients. The changes were progressive during the follow-up time, which was up to 20 years.

Developmental aspects of type II lissencephaly. Comparative study of dysplastic lesions in fetal and post-natal brains

We report neuropathological studies of five cases of type II lissencephaly from three fetuses and two infants. This comparative study allowed us to determine the developmental course of the cerebral lesions. Two distinct developmental events seem to generate this type of brain malformation: firstly, an early disturbance in cortex formation, which results both from a disorder of radial migration and a pial barrier disruption; secondly, a late perturbation of cerebral surface organization, resulting in fusion of the cerebral surface. All these features can be related to a primitive meningeal pathology, and more generally, to a neurocristopathy. Accordingly to our observations, this brain malformation appears during both migrational and post-migrational stages and may be considered more like a polymicrogyria than a lissencephaly.

Muscle and brain disease: an update

A number of syndromes included under this rubric are considered, and their main features discussed. The congenital muscular dystrophy of the Fukuyama type as it occurs in Japan and in the western world are almost certainly the same condition. The muscle disorder is associated with cerebral lesions which may be due to an arrest of neural migration or to demyelination. Muscle, eye and brain disease, or Santavuori's syndrome, shows ocular abnormalities, as well as those of the muscle and brain, as does the Walker-Warburg syndrome. In the latter disorder the cerebral lesions tend to be more severe, and it is more rapidly fatal. The manifestations of all these syndromes undoubtedly overlap, but there has been controversy on the question of their identity. Are they separate entities, or are they different expressions of a similar genetic disorder? The genes for all these conditions will have to be isolated to see if the different phenotypes are alleles of the same gene, or not. Some of the arguments, for and against, are presented.

Ocular findings in Walker-Warburg syndrome

Ocular symptoms are frequently observed in Walker-Warburg (WWS) and associated syndromes. The majority of patients present with malformations of the anterior segment and severe retinal dysplasia. We report on the findings in a female patient with WWS who died at the age of 9 months. Major ocular findings were: severe iridocorneal malformation, a membrane-like structure of the lens and funnel-shaped retinal dysplasia. The retina presented various grades of differentiation with rosettes and atypical sequences of cells, e.g. ganglion cells intermingled between granular layers. The anterior part of the retina presented as a primitive homogeneous layer with a cell-free space that might be interpreted as the primary optic ventricle. This finding suggests that we are dealing with a primary dysplastic non-attachment rather than a real detachment of the retina in WWS. The malformation of the anterior segment was not typical of the Peters' anomaly, as usually described in WWS, but of Rieger's syndrome.

Clinical variation within sibships in Fukuyama-type congenital muscular dystrophy

A family in which three siblings were affected with severe cerebral malformations in association with ocular anomalies and muscle disease is reported. One sibling was diagnosed as having Fukuyama type congenital muscular dystrophy (FCMD) because he showed severe hypotonia with dystrophic findings on a muscle biopsy in addition to pachygyria on CT. At the age of 3 years, retinal detachment developed in both eyes. Another sibling exhibited at birth such characteristic features as pachygyria, cephalocele, hydrocephalus, retinal detachment in both eyes, elevated serum creatine kinase activity and arthrogryposis multiplex congenita. We consider these findings to be more consistent with Walker-Warburg syndrome (WWS) than with FCMD. Anencephaly found in the third sibling was regarded as WWS with extreme brain abnormality. The appearance of two syndromes (FCMD and WWS) in the three members of the same family suggests that these syndromes could be allelic with variable phenotypes.

Congenital muscular dystrophies--problems of classification

The classification of congenital muscular dystrophies (CMD), based on perceived clinical and morphological similarities or differences, is controversial. CMD without cerebral involvement has sometimes been divided into a mild and a severe form. This distinction is, however, arbitrary and not uncontested. Whether Ullrich's disease, formerly called atonic-sclerotic dystrophy, is a disease entity and if so, whether it is a primary muscle disorder, is uncertain. CMD without cerebral involvement is inherited in an autosomal recessive fashion in the great majority of cases. CMDs with cerebral involvement are usually classified into at least three forms: the Fukuyama type of CMD, occurring almost exclusively in Japanese patients; CMD with hypomyelination, sometimes also called the occidental type of cerebromuscular dystrophy; and Walker-Warburg syndrome. Muscle-eye-brain disease, described in a number of Finnish patients, may or may not belong in this last category. In CMD with cerebral involvement inheritance is also autosomal recessive. It is possible that single sporadic cases are phenocopies due to infectious or other exogenous causes. Reports of clinical and morphological findings from an increasing number of patients show a high degree of variability within and, on the other hand, certain similarities between the forms of CMD with cerebral involvement. In addition, neuroradiological changes are also found with increasing frequency in CMD patients without clinical neuropsychological abnormalities. It is not unreasonable to speculate that molecular genetic techniques will reveal in the near future a variable defect in one gene locus or defects in a few gene loci as the cause of the various clinical forms of CMDs.