Brain alterations in the classical form of congenital muscular dystrophy. Clinical and neuroimaging follow-up of 12 cases and correlation with the expression of merosin in muscle

Merosin-deficient congenital muscular dystrophy with cerebral white matter changes: a clue to its diagnosis beyond infancy

A 6-year-old boy born by a third-degree consanguineous marriage presented with progressive muscle weakness and delayed motor milestones noticed in early infancy with preserved language and social milestones. Examination revealed generalised hypotonia and hyporeflexia. Baseline haematological and biochemical investigations were normal except for mildly elevated creatine kinase. Provisional diagnosis of congenital myopathy was entertained. We performed brain imaging to look for abnormalities associated with congenital muscular dystrophy even though there were only features of myopathy with normal mentation. An MRI of the brain revealed periventricular and subcortical white matter hyperintensities suggestive of leucoencephalopathy. Muscle biopsy findings were consistent with degenerative muscle changes and immunohistochemical staining for merosin was negative, thus confirming the diagnosis of merosin-deficient congenital muscular dystrophy. Supportive care in the form of physiotherapy was initiated. The family was offered genetic counselling in their second pregnancy and immunohistochemistry at 12 weeks confirmed the fetus to be affected, which was then terminated.

Sequential neuroradiological and neurophysiological studies in a Japanese girl with merosin-deficient congenital muscular dystrophy

We describe the early manifestation and sequential assessment of the central and peripheral nervous system in a Japanese girl with merosin-deficient congenital muscular dystrophy. She showed severe hypotonia (''floppy infant") and suffered mild respiratory failure postnatally. Serum creatine kinase was elevated to 11,487 IU/L. The muscle biopsy showed dystrophic changes with negative expression of merosin (laminin α2), thereby confirming merosin-deficient congenital muscular dystrophy. Her motor milestones were severely delayed, but she could sit without support at the age of 3 years. After 3 years, her motor ability deteriorated and by the age of 5 years, she could not sit and control her neck. Magnetic resonance imaging (MRI) at 2 months of age revealed patterns that were appropriate for her age. At 1 year of age, the T2 weighted images showed diffuse high signal intensities throughout the centrum semiovale, and periventricular and subcortical white matter of the frontal and occipital lobes, while the U fibers, the corpus callosum and the internal capsule were spared. At the age of 7 years, these white matter abnormalities decreased. MR spectroscopy (MRS) revealed normal values of N-acetylaspartate (NAA)/creatine (Cr) and choline (Cho)/Cr metabolite ratios as well as slightly increased myoinositol (mI)/Cr metabolite ratios. Neurophysiological motor nerve conduction velocity (MCV) and compound muscle action potential (CMAP) of the median nerve were in the normal range at the age of 2 months. After the child reached 1 year of age, the MCV and CMAP lagged behind those of healthy controlled children. The sensory nerve conduction velocity of the median nerve demonstrated a mild delay at the age of 15 months. It improved to normal range at the age of 6 years but decreased at 7 years of age. These sequential findings suggest not only that muscular degeneration and dysmyelination had occurred but also that various other factors, including demyelination and the vasogenic system, may influence the pathology of MDC1A.

Biological role of dystroglycan in Schwann cell function and its implications in peripheral nervous system diseases

Dystroglycan is a central component of the dystrophin-glycoprotein complex (DGC) that links extracellular matrix with cytoskeleton, expressed in a variety of fetal and adult tissues. Dystroglycan plays diverse roles in development and homeostasis including basement membrane formation, epithelial morphogenesis, membrane stability, cell polarization, and cell migration. In this paper, we will focus on biological role of dystroglycan in Schwann cell function, especially myelination. First, we review the molecular architecture of DGC in Schwann cell abaxonal membrane. Then, we will review the loss-of-function studies using targeted mutagenesis, which have revealed biological functions of each component of DGC in Schwann cells. Based on these findings, roles of dystroglycan in Schwann cell function, in myelination in particular, and its implications in diseases will be discussed in detail. Finally, in view of the fact that understanding the role of dystroglycan in Schwann cells is just beginning, future perspectives will be discussed.

Cognition and adaptive skills in myotonic dystrophy type 1: a study of 55 individuals with congenital and childhood forms

AIMS

To investigate cognitive abilities and adaptive skills in children and adolescents with myotonic dystrophy type 1 (DM1) and correlate the findings to the cytosine-thymine-guanine (CTG) repeat expansion size.

METHOD

Cognitive level was assessed in 55 children and adolescents with DM1 (31 males, 24 females; mean age 12y 1mo, SD 5y 1mo; range 2y 7mo-21y 5mo) divided into the following categories: severe congenital DM1 (n=19), mild congenital DM1 (n=18), and childhood DM1 (n=18). The Griffiths Mental Developmental Scale, the Wechsler Scales, and the Vineland Adaptive Behavior Scales (VABS) for adaptive skills were used for this purpose.

RESULTS

Learning disability was found in 95% of the severe congenital group, 83% of the mild congenital group, and 89% of the childhood DM1 group. The more severe the form of DM1, the lower the full-scale IQ (FSIQ; r(s)=0.28, p=0.044). The individuals with severe congenital and childhood DM1 had a significantly higher verbal IQ than performance IQ (severe congenital: mean difference 5.7, SD 5.7, p=0.008; childhood DM1: mean difference 9.8, SD 18.0, p=0.038). CTG repeat expansion correlated negatively with FSIQ (r(s)=-0.63, p<0.006). Almost all participants showed poor results on the VABS. There was a positive relationship between cognitive level and adaptive skills in the mild congenital (r(s)=0.95, p<0.01) and childhood DM1 groups (r(s)=0.92, p<0.01).

INTERPRETATION

Children and adolescents with DM1 exhibit significant cognitive and adaptive problems.

Autism spectrum conditions in myotonic dystrophy type 1: a study on 57 individuals with congenital and childhood forms

Myotonic dystrophy type 1 (DM1) is an autosomal dominant disorder, caused by an expansion of a CTG triplet repeat in the DMPK gene. The aims of the present study were to classify a cohort of children with DM1, to describe their neuropsychiatric problems and cognitive level, to estimate the size of the CTG expansion, and to correlate the molecular findings with the neuropsychiatric problems. Fifty-seven children and adolescents (26 females; 31 males) with DM1 (CTG repeats > 40) were included in the study. The following instruments were used: Autism Diagnostic Interview-Revised (ADI-R), 5-15, Griffiths Mental Development Scales, and the Wechsler Scales. Based on age at onset and presenting symptoms, the children were divided into four DM1 groups; severe congenital (n = 19), mild congenital (n = 18), childhood (n = 18), and classical DM1 (n = 2). Forty-nine percent had an autism spectrum disorder (ASD) and autistic disorder was the most common diagnosis present in 35% of the subjects. Eighty-six percent of the individuals with DM1 had mental retardation (MR), most of them moderate or severe MR. ASD was significantly correlated with the DM1 form; the more severe the form of DM1, the higher the frequency of ASD. The frequency of ASD increased with increasing CTG repeat expansions. ASD and/or other neuropsychiatric disorders such as attention deficit hyperactivity disorder, and Tourette's disorder were found in 54% of the total DM1 group. In conclusion, awareness of ASD comorbidity in DM1 is essential. Further studies are warranted to elucidate the molecular etiology causing neurodevelopmental symptoms such as ASD and MR in DM1.

Merosin-negative congenital muscular dystrophy: diffusion-weighted imaging findings of brain

Merosin-negative congenital muscular dystrophy is a rare genetic disease of childhood involving the central and peripheral nervous system. There were high signal intensities throughout the centrum semiovale, periventricular, and sub-cortical white matters on T2-weighted images in a 4-year-old girl with merosin-negative congenital muscular dystrophy. An apparent diffusion coefficient map revealed increased signal intensity and apparent diffusion coefficient values in the periventricular and deep white matters. It may be attributable to increased water content in the white matter because of an abnormal blood-brain barrier rather than to decreased or abnormal myelination.

Nonmuscular involvement in merosin-negative congenital muscular dystrophy

The spectrum of nonmuscular involvement in six children with merosin-negative congenital muscular dystrophy is described. In all children, biochemical, neuroradiologic, cardiac, and neurophysiologic studies were performed. Cerebral structures that were myelinated at gestation, including internal capsule, corpus callosum, brainstem, and cerebellar white matter, demonstrated no abnormalities, whereas the periventricular and subcortical white matter, which were myelinated in the first postnatal year, demonstrated signs of leukoencephalopathy. Cerebrospinal fluid analysis revealed an elevated albumin cerebrospinal fluid to serum ratio in the younger children. Electroencephalogram results were abnormal in the two elder children. One child suffered from congestive cardiomyopathy. The increase in nerve conduction velocity in these children over the years lagged behind those of healthy patients, pointing to a demyelinating neuropathy. We conclude that in merosin-negative congenital muscular dystrophy patients, nonmuscular involvement includes the central and peripheral nervous system and the heart. The pattern of myelination of the brain and nerve conduction slowing suggests a myelination arrest. Merosin deficiency can give rise to a congestive cardiomyopathy, which is of no clinical relevance in the majority of children.

The expanding phenotype of laminin alpha2 chain (merosin) abnormalities: case series and review

Initial reports of patients with laminin alpha2 chain (merosin) deficiency had a relatively homogeneous phenotype, with classical congenital muscular dystrophy (CMD) characterised by severe muscle weakness, inability to achieve independent ambulation, markedly raised creatine kinase, and characteristic white matter hypodensity on cerebral magnetic resonance imaging. We report a series of five patients with laminin alpha2 deficiency, only one of whom has this severe classical CMD phenotype, and review published reports to characterise the expanded phenotype of laminin alpha2 deficiency, as illustrated by this case series. While classical congenital muscular dystrophy with white matter abnormality is the commonest phenotype associated with laminin alpha2 deficiency, 12% of reported cases have later onset, slowly progressive weakness more accurately designated limb-girdle muscular dystrophy. In addition, the following clinical features are reported with increased frequency: mental retardation (~6%), seizures (~8%), subclinical cardiac involvement (3-35%), and neuronal migration defects (4%). At least 25% of patients achieve independent ambulation. Notably, three patients with laminin alpha2 deficiency were asymptomatic, 10 patients had normal MRI (four with LAMA2 mutations reported), and between 10-20% of cases had maximum recorded creatine kinase of less than 1000 U/l. LAMA2 mutations have been identified in 25% of cases. Sixty eight percent of these have the classical congenital muscular dystrophy, but this figure is likely to be affected by ascertainment bias. We conclude that all dystrophic muscle biopsies, regardless of clinical phenotype, should be studied with antibodies to laminin alpha2. In addition, the use of multiple antibodies to different regions of laminin alpha2 may increase the diagnostic yield and provide some correlation with severity of clinical phenotype.

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.

Merosin and congenital muscular dystrophy

Merosin (also called as Laminin-2) is an isoform of laminin comprised of the alpha2, beta1 and gamma1 chains. In European populations, half of the patients with classical congenital muscular dystrophy have mutations of the LAMA2 gene (6q22-23) and present reduced or absence of laminin alpha2 chain. This form is generally referred to as merosin-deficient CMD. Merosin-deficient CMD is characterized by involvement of not only skeletal muscle but also central and peripheral nervous systems: Extensive brain white matter abnormalities are found by magnetic resonance imaging (MRI). However, most patients show no mental retardation. Recent case studies reported that some patients have several structural abnormalities such as abnormal cerebral cortical gyration, hypoplasia of cerebellum and pons, and dilation of ventricles. At present, functions of merosin related to muscle degeneration have not been fully elucidated. In addition, the mechanisms responsible for pathogenesis of diffuse brain white matter abnormalities remain to be determined. As mouse models for merosin-deficient CMD, three spontaneous mutants(dy, dy(2J), dy(PAS1)) and two mutants named dy(W) and dy(3K) by targeted gene disruption have been reported. These mice will help to elucidate the pathogenesis of merosin-deficient CMD and serve to develop therapy.

Cognitive abilities in children with congenital muscular dystrophy: correlation with brain MRI and merosin status

The aim of the study was to evaluate whether children with merosin-positive or merosin-deficient congenital muscular dystrophy (CMD) show any cognitive impairment and whether this is related to brain abnormalities on magnetic resonance imaging (MRI). Twenty-two patients (age range: 5.8-15.3 years) were assessed by the Wechsler Intelligence Scales. Twelve were merosin-positive and ten merosin-deficient. One child had severe mental retardation and could not be tested. The full scale IQ in the remaining 21 ranged from 51 to 134, the verbal IQ ranged from 78 to 136 and the performance from 51 to 136. Of the twelve children with normal merosin one had a mild delay (IQ < 75) and two were borderline (IQ 75-95). Of the ten children with merosin-deficiency, one showed severe mental retardation and could not be tested, one showed a mild delay and two had borderline results. While the children with merosin deficiency with the typical diffuse white matter changes on MRI had normal scores, the children who in addition had cerebellar hypoplasia had lower performance IQ. The child with cortical dysplasia had severe mental retardation. Our results suggest that the spectrum of cognitive abilities in CMD is very wide even within genetically homogeneous conditions.

Laminin-2/integrin interactions enhance myelin membrane formation by oligodendrocytes

To examine the role of extracellular matrix (ECM)/integrin interactions in myelination we have analyzed oligodendrocyte differentiation and myelin membrane formation in oligodendrocytes grown in cell culture. We have found that the ECM substrates fibronectin, vitronectin, and laminin-2 (merosin) have no effect on differentiation, as measured by the appearance of myelin basic protein-expressing cells, but that laminin-2 substrates dramatically enhance myelin membrane formation. Blocking antibody and immunolocalization studies suggest that this effect is mediated via 1 integrins. The v integrins expressed on oligodendrocytes, in contrast, are less effective at promoting membrane formation. These results show that the interaction between laminin-2 expressed in white matter tracts and oligodendrocyte laminin-binding integrins may be an important part of the signalling mechanisms that stimulate oligodendrocytes to elaborate the extensive myelin membrane required to wrap the axon and form the myelin sheath. The results also provide a logical explanation for the abnormalities of myelination observed in humans with merosin-deficient congenital muscular dystrophy.

Merosin-deficient congenital muscular dystrophy: the spectrum of brain involvement on magnetic resonance imaging

Children with merosin-deficient congenital muscular dystrophy (CMD) have striking white matter changes on T-2 weighted brain magnetic resonance imaging (MRI). There have been occasional cases with structural abnormalities, mainly involving the occipital cortex. We report our brain imaging findings in 14 children with merosin-deficient CMD. Ten cases had a severe reduction or absence of merosin on immunocytochemistry and four cases had partial reduction. All 14 cases had white matter changes, which appeared after the first 6 months of life and persisted with time. The changes were diffuse and the oldest child scanned (14 years) also showed involvement of the U fibres. Five children with total absence of merosin also had structural abnormalities. One child had moderate mental retardation and epilepsy, mainly characterised by complex partial seizures, with atypical absences, which had been difficult to treat. Brain MRI showed marked occipital agyria and pontocerebellar hypoplasia. The gyral pattern of the rest of the brain looked normal. The four other cases, all with normal intelligence, also had cerebellar hypoplasia with variable involvement of the pons. They did not, however, have neuronal migration defects. It is recognised that several forms of congenital muscular dystrophy, namely Fukuyama CMD, muscle-eye-brain disease and Walker-Warburg syndrome, have structural brain abnormalities and associated severe mental retardation. Our cases demonstrate that a range of structural malformations can also be found in a significant number of children with merosin-deficient CMD.

Visual function in children with merosin-deficient and merosin-positive congenital muscular dystrophy

This study evaluates whether abnormalities of visual function are present in children with congenital muscular dystrophy and whether these, if present, are associated with merosin status or magnetic resonance imaging (MRI) findings. Twenty children (age range 5-17 years) with a diagnosis of classical congenital muscular dystrophy were assessed on visual acuity, stereopsis, and visual fields and the results compared with merosin status and MRI findings. Visual-evoked potential results were available for 14 of 20 children. All 20 children revealed normal results on all the clinical tests assessing visual function, irrespective of their merosin status or of MRI findings. Visual-evoked potentials were normal in the children with merosin-positive congenital muscular dystrophy but were abnormal in those with merosin deficiency. Unlike the other forms of congenital muscular dystrophy, which are associated with structural brain changes and eye involvement, visual function was always normal in the classical form of congenital muscular dystrophy. Interestingly, visual function was normal also in the group of children with merosin-deficient congenital muscular dystrophy who manifested white matter changes involving the occipital lobes on MRI and abnormal visual evoked potentials. Further studies are needed to specify the nature of the white matter changes observed with MRI and the reason for the dissociation between clinical and neurophysiologic findings.

Merosin-deficient congenital muscular dystrophy and cortical dysplasia

Congenital muscular dystrophy (CMD) encompasses a heterogenous group of muscle disorders with autosomal recessive inheritance, characterized by muscular weakness and hypotonia at birth or within the first few months of life and developmental delay. Merosin-deficient CMD is a clinically distinct form which may be associated with significant abnormalities of the brain detectable by neuroimaging. We report two siblings of consanguineous parents with merosin-deficient CMD in an Irish family who in addition to the characteristic white matter abnormalities on neuroimaging, had occipital dysplasia. Clinical, electrophysiological muscle biopsy findings and neuroimaging were very similar in both cases. Although merosin-deficient CMD with white matter abnormalities on neuroimaging is well documented in the literature, the association with occipital dysplasia has only rarely been reported. The appearance of an identical cortical defect in these siblings suggests an underlying genetic mechanism.