Merosin-positive congenital muscular dystrophy with transient brain dysmyelination, pontocerebellar hypoplasia and mental retardation

Development of the human cerebellum and its disorders

The cerebellum arises from two anatomically and molecularly different proliferative compartments: the cerebellar ventricular zone and the rhombic lip. The protracted development makes the cerebellum vulnerable to a broad spectrum of developmental disorders, of which the more frequent (the Dandy-Walker and related malformations and the pontocerebellar hypoplasias) are discussed in this article. Several genes for congenital malformations of the human cerebellum have recently been identified, including genes causing Joubert syndrome, the Dandy-Walker malformation, and pontocerebellar hypoplasias.

Morphological spectrum of prenatal cerebellar disruptions

There is increasing evidence that the cerebellum is susceptible to both prenatal infections and haemorrhages as well as being vulnerable in extremely preterm babies, but not to perinatal and postnatal hypoxic-ischaemic injuries. Starting with the imaging appearance we describe and illustrate a spectrum of prenatal cerebellar disruptions: cerebellar agenesis; unilateral cerebellar hypoplasia; unilateral cerebellar cleft; global cerebellar hypoplasia; vanishing cerebellum in myelomeningocele; and disruption of cerebellar development in preterm infants. We discuss neuroradiological characteristics, possible disruptive events, and clinical findings in the different morphological patterns. Remarkably, the same disruptive agent can cause different neuroradiological patterns, which appear likely to represent a morphological spectrum. The analysis of imaging patterns is crucial in recognising cerebellar disruptions. Recognition of cerebellar disruptions and their differentiation from cerebellar malformations is important in terms of diagnosis, prognosis, and genetic counselling.

Pontocerebellar hypoplasia type 1

Pontocerebellar hypoplasias are heterogeneous disorders that share a reduction in the size of brainstem and cerebellum. We describe a patient with features of the rare combination of pontocerebellar hypoplasia and spinal motor neuron disease. Parental consanguinity, low Apgar scores, facial weakness, dysphagia, tongue fasciculations, stridor, generalized hypotonia, severe muscle weakness, areflexia, and congenital joint contractures were evident. Cranial magnetic resonance imaging revealed a small cerebellum and brainstem, and a muscle biopsy revealed neurogenic changes. These abnormalities suggested pontocerebellar hypoplasia type 1.

Severe, fetal-onset form of olivopontocerebellar hypoplasia in three sibs: PCH type 5?

We present three siblings with a precise onset of fetal seizure-like activity who had severe olivopontocerebellar hypoplasia (OPCH) and degeneration. Autopsies at 20, 27, and 37 weeks gestation showed diffuse central nervous system volume loss that was most marked for the cerebellum and brain stem structures. Neuropathological abnormalities included dysplastic, C-shaped inferior olivary nuclei, absent or immature dentate nuclei, and cell paucity more marked for the cerebellar vermis than the hemispheres. Delayed development was seen in layer 2 of the cerebral cortex and in Purkinje cells of the cerebellum. Prenatal monitoring defined a developmental window of 16-18 weeks gestation when ultrasonic assessment of cerebellar width was used for prenatal diagnosis. We discuss our findings in the context of the differential diagnosis for infantile (O)PCH and propose a classification scheme for the pontocerebellar hypoplasias. These patients represent the earliest reported with OPCH and provide unique information regarding the developmental neuropathology of this condition.

Brain MRI abnormalities in muscular dystrophy due to FKRP mutations

INTRODUCTION

FKRP mutations cause a muscular dystrophy which may present in the neonatal period (MDC1C) or later in life (LGMD2I). Intelligence and brain imaging have been previously reported as being normal in FKRP-associated muscular dystrophy, except in rare cases presenting with mental retardation associated with structural brain abnormalities.

PATIENTS AND METHODS

We studied cerebral MRIs in twelve patients with FKRP-associated muscular dystrophy presenting in infancy or early childhood, at ages between 14 months and 43 years. Two patients had severe cognitive deficits, four had mild-moderate mental retardation and the rest were considered to have normal intelligence. All, but one were wheelchair-bound and 7 were mechanically ventilated.

RESULTS

Brain MRI was abnormal in 9 of 12 patients. Brain atrophy was seen in 8 patients. One child had isolated ventricular enlargement at 4 years. Cortical atrophy involved predominantly temporal and frontal lobes and was most important at later ages. In two cases with serial images this atrophy seemed progressive. Three patients, two with severe and one with moderate mental retardation, showed structural abnormalities of the posterior fossa with hypoplasia of the vermis and pons, and cerebellar hemispheric cysts. These abnormalities were stable with time. Two of these three patients also showed diffuse white matter abnormalities in early childhood, which regressed with time.

CONCLUSIONS

MRI abnormalities are common in patients with FKRP-associated muscular dystrophy presenting at birth or in early childhood. Progressive brain atrophy is the most frequent finding. Posterior fossa malformations and transient white matter changes may be seen in patients with associated mental retardation.

Congenital malformations of the human brainstem

Congenital disorders of the brainstem often result in multiple severe neurodevelopmental problems. With the advent of magnetic resonance imaging and discovery of genes directing brainstem formation, a more coherent clinical picture of these disorders is emerging. Proper evaluation, management, and counseling for these disorders rests on the clinician having a framework through which to approach them.

Merosin-deficient congenital muscular dystrophy with mental retardation and cerebellar cysts, unlinked to the LAMA2, FCMD, MEB and CMD1B loci, in three Tunisian patients

We report three Tunisian patients affected by congenital muscular dystrophy with mental retardation and cerebellar cysts on cranial magnetic resonance imaging. The clinical features were characterized by hypotonia at birth, joint contractures associated with severe psychomotor retardation, absence of speech, inability to walk in three patients, but calf hypertrophy was noted only in two patients. Brain magnetic resonance imaging showed several cerebellar cysts and vermis hypoplasia in all of the patients. Abnormality of the white matter was present in two patients. The pattern of gyration was normal in all cases. Serum creatine kinase was elevated in all three cases and their muscle biopsy showed dystrophic changes compatible with congenital muscular dystrophy. The immunohistochemical analysis of the skeletal muscle revealed partial merosin deficiency, more pronounced for the N-terminal antibody. Linkage analysis excluded congenital muscular dystrophy loci on chromosomes 6q22, 9q31, 1p32 and 1q42. These patients constituted a particular form of congenital muscular dystrophy with a combination of severe motor delay, mental retardation, partial merosin deficiency and cerebellar cysts. Two patients showed white matter abnormalities on magnetic resonance imaging and hypertrophy of the calves. These cases, in addition to those reported previously, confirmed the large phenotypic variability in the group of secondary merosin deficiency congenital muscular dystrophy.

Congenital muscular dystrophy with adducted thumbs, ptosis, external ophthalmoplegia, mental retardation and cerebellar hypoplasia: a novel form of CMD

At least six different forms of congenital muscular dystrophy are associated with structural changes of the central nervous system, and three of these have been mapped: merosin-deficient congenital muscular dystrophy on chromosome 6q2, Fukuyama congenital muscular dystrophy on chromosome 9q31, and muscle eye brain disease on chromosome 1p32. Walker-Warburg syndrome, congenital muscular dystrophy with calf hypertrophy, pontocerebellar hypoplasia, and normal eyes, and congenital muscular dystrophy with severe mental retardation and cerebellar cysts are nosologically distinct and have been excluded from the known congenital muscular dystrophy loci with structural changes of the central nervous system. Here, we describe a novel congenital muscular dystrophy syndrome which is phenotypically distinct from the recognized forms of congenital muscular dystrophy with brain involvement. Two siblings, a boy and a girl, were born to consanguineous parents from Sicily. Both children were born with adducted thumbs and toe contractures. They were floppy from birth, walked late, showed profound generalized muscle weakness including facial muscles, elevated creatine kinase levels of 200-700U/l, and histological changes compatible with muscular dystrophy. In addition, both showed ptosis, external ophthalmoplegia, mild mental retardation, and mild cerebellar hypoplasia on MRI. Immunocytochemistry showed normal expression of muscle membrane proteins including laminin alpha 2, laminin beta 2, and alpha-dystroglycan. Linkage analysis excluded the candidate loci on chromosomes 6q2, 9q31, and 1q32. The gene locus for congenital muscular dystrophy 1B, MDC 1B, on chromosome 1q42 was also excluded. Adducted thumbs are a distinct clinical sign that has not been reported in congenital muscular dystrophy before and should facilitate recognition of further patients with this disorder.

Merosin-positive congenital muscular dystrophy with mental retardation, microcephaly and central nervous system abnormalities unlinked to the Fukuyama muscular dystrophy and muscular-eye-brain loci: report of three siblings

Classical merosin (2 laminin)-positive congenital muscular dystrophy is a heterogeneous subgroup of disorders; a few cases characterized by severe mental retardation, brain involvement and no ocular abnormalities were called Fukuyama-like congenital muscular dystrophy. We report a family of healthy non-consanguineous parents, with four affected siblings, of which one died at the age of 7 months due to an intercurrent illness, who presented congenital hypotonia, severe mental retardation, microcephaly, delayed psychomotor development, generalized muscular wasting and weakness with mild facial involvement, calf pseudohypertrophy, joint contractures and areflexia. Muscle biopsy disclosed severe muscular dystrophy. Immunostaining for laminin 2 80 kDa and clone Mer3/22B2 monoclonal antibodies, 1 and 1 chain was preserved. Magnetic resonance imaging findings were consistent with pontocerebellar hypoplasia, bilateral opercular abnormalities and focal cortical dysplasia as well as minute periventricular white matter changes. Clusters of small T2-weighted focal hyperintensities in both cerebellar hemispheres consistent with cysts were observed in two of the three siblings studied with magnetic resonance imaging. Ophthalmologic and cardiologic examination was normal. Haplotype analysis using microsatellite markers excluded the Fukuyama congenital muscular dystrophy, LAMA2 and muscle-eye-brain disease loci. Thus, a wider spectrum of phenotypes, gene defects and protein deficiencies might be involved in congenital muscular dystrophy with brain abnormalities.

Ataxia and congenital muscular dystrophy: the follow-up of a new specific phenotype

Cerebellar hypoplasia may, at neuroimaging studies, be found in association with congenital muscular dystrophy (CMD), although it is an extremely rare occurrence. We here report on three CMD patients who underwent a longitudinal evaluation of clinical and neuroimaging features for a mean period of 18 years. Case 1, a 22-year-old woman, and cases 2 and 3, brothers aged 26 and 20 years, respectively, had presented a mild to moderate muscular weakness and increased serum creatine kinase (CK) levels since birth. All cases were diagnosed in the first years of life, with identification of evident dystrophic changes at muscle biopsy and moderate to severe cerebellar hypoplasia at brain computed tomography (CT) scan. Subsequently, all the patients underwent a second muscle biopsy, with immunostaining and immunoblot analysis, which showed normal values for merosin, dystrophin and dystrophin-related proteins. During the longitudinal study, the patients underwent repeated neurological and psychiatric examinations, serum CK controls, intellectual ability assessments and neuroimaging evaluations (CT and/or magnetic resonance imaging (MRI)). In all cases, these investigations indicated a mild to moderate deficit in the proximal muscles and a clear-cut cerebellar syndrome which, it was assumed, had been present since the first years. The patients also presented some intellectual difficulties, with an IQ of 0.69 in case 1, 0.83 in case 2 and 0.61 in case 3. The clinical course of all the patients was static, and all symptoms of the combined muscle and brain involvement persisted. Nor were any changes in the cerebellar hypoplasia observed at repeat MRIs. Findings obtained by us on the longitudinal study and a review of the literature indicate that cerebellar hypoplasia and merosin-positive CMD constitute a particular clinical phenotype, mainly characterized by an ataxic syndrome associated with a non-severe muscular involvement and a possible mild intellectual impairment.

Heterogeneity of classic congenital muscular dystrophy with involvement of the central nervous system: report of five atypical cases

A heterogeneous group of patients with congenital muscular dystrophy associated with clinical or radiologic central nervous system involvement other than the severe classic form with merosin deficiency, muscle-eye-brain disease, and Walker-Warburg syndrome is described. A probable hereditary or familial occurrence could be suggested in all patients. One merosin-positive patient presented severe motor incapacity and cerebral atrophy without any clinical manifestation of central nervous system involvement. A second patient, also merosin-positive, had moderate motor and mental handicap, and epilepsy with no changes in neuroimaging. A third patient, found to have partial merosin deficiency by muscle biopsy, manifested severe psychomotor retardation and cerebral atrophy with foci of abnormal white-matter signal on magnetic resonance imaging. Finally, two merosin-positive siblings with microcephaly, mental retardation, and an incapacitating progressive neuromuscular course, exhibited cataracts without defects of neuronal migration or brain malformation. This report emphasizes the broad clinical spectrum and heterogeneity of merosin-positive congenital muscular dystrophy with associated central nervous system involvement, and illustrates the importance of further studies on clinical, immunohistochemical, and genetic grounds for identifying new subsets of congenital muscular dystrophy.

Inherited disorders of the extracellular matrix

Primary and secondary defects in extracellular matrix proteins emphasize the role of these proteins in neuromuscular disorders; mutations have been found in the genes for the laminin-alpha 2 chain, for all three alpha chains of collagen VI and for integrin alpha 2. Secondary alterations in protein expression occur in association with these primary defects, and in other disorders they implicate the extracellular matrix. Animal models are helping to elucidate the function of some of these proteins, to develop therapeutic strategies and to suggest candidate proteins for other neuromuscular disorders.