Brain MRI abnormalities in muscular dystrophy due to FKRP mutations

The first report of two homozygous sequence variants in FKRP and SELENON genes associated with syndromic congenital muscular dystrophy in Iran: Further expansion of the clinical phenotypes

BACKGROUND

Congenital muscular dystrophy (CMD) refers to hypotonia and delayed motor development that is manifested at or near the birth. Additional presentations have been observed in CMD syndromes.

METHODS

Thorough clinical examinations were performed on two unrelated Iranian families with typical symptoms of CMD and uncommon features such as intellectual disability and nephrolithiasis. The genomic DNA of probands were subjected to whole exome sequencing. Following the detection of candidate variants with a bioinformatic pipeline, the familial co-segregation analysis was carried out using polymerase chain reaction-based Sanger sequencing.

RESULTS

We identified a missense homozygous variant in the fukutin-related protein (FKRP) gene (c.968G>A, p.Arg323His) related to CMD-dystroglycanopathy type B5 (MDDGB5) and a frameshift homozygous variant in the selenoprotein N (SELENON) gene (c.1446delC, p.Asn483Thrfs*11) associated with congenital rigid-spine muscular dystrophy 1 (RSMD1), which were completely segregated with the phenotypes in the families. These variants were not found in either the 1000 Genomes Project or the Exome Aggregation Consortium. The present study provides the first report of these homozygous sequence variants in Iran. Moreover, our study was the first observation of nephrolithiasis in FKRP-related dystroglycanopathy and intellectual disability in SELENON-related myopathies. Based on in silico studies and molecular docking, these variations induced pathogenic effects on the proteins.

CONCLUSIONS

Our findings extend the genetic database of Iranian patients with CMD and, in general, the phenotypical spectrum of syndromic CMD. It is recommended to consider these variants for a more accurate clinical interpretation, prenatal diagnosis and genetic counseling in families with a history of CMD, especially in those combined with cognitive impairments or renal dysfunctions.

Discovery of Novel Therapeutics for Muscular Dystrophies using Zebrafish Phenotypic Screens

The recent availability and development of mutant and transgenic zebrafish strains that model human muscular dystrophies has created new research opportunities for therapeutic development. Not only do these models mimic many pathological aspects of human dystrophies, but their small size, large clutch sizes, rapid ex utero development, body transparency, and genetic tractability enable research approaches that would be inconceivable with mammalian model systems. Here we discuss the use of zebrafish models of muscular dystrophy to rapidly screen hundreds to thousands of bioactive compounds in order to identify novel therapeutic candidates that modulate pathologic phenotypes. We review the justification and rationale behind this unbiased approach, including how zebrafish screens have identified FDA-approved drugs that are candidates for treating Duchenne and limb girdle muscular dystrophies. Not only can these drugs be re-purposed for treating dystrophies in a fraction of the time and cost of new drug development, but their identification has revealed novel, unexpected directions for future therapy development. Phenotype-driven zebrafish drug screens are an important compliment to the more established mammalian, target-based approaches for rapidly developing and validating therapeutics for muscular dystrophies.

Functional and cellular localization diversity associated with Fukutin-related protein patient genetic variants

Genetic variants in Fukutin-related protein (FKRP), an essential enzyme of the glycosylation pathway of α-dystroglycan, can lead to pathologies with different severities affecting the eye, brain, and muscle tissues. Here, we generate an in vitro cellular system to characterize the cellular localization as well as the functional potential of the most common FKRP patient missense mutations. We observe a differential retention in the endoplasmic reticulum (ER), the indication of misfolded proteins. We find data supporting that mutant protein able to overcome this ER-retention through overexpression present functional levels comparable to the wild-type. We also identify a specific region in FKRP protein localized between residues 300 and 321 in which genetic variants found in patients lead to correctly localized proteins but which are nevertheless functionally impaired or catalytically dead in our model, indicating that this particular region might be important for the enzymatic activity of FKRP within the Golgi. Our system thus allows the functional testing of patient-specific mutant proteins and the identification of candidate mutants to be further explored with the aim of finding pharmacological treatments targeting the protein quality control system.

Clinical, genetic, and pathologic characterization of FKRP Mexican founder mutation c.1387A>G

Objective

To characterize the clinical phenotype, genetic origin, and muscle pathology of patients with the FKRP c.1387A>G mutation.

Methods

Standardized clinical data were collected for all patients known to the authors with c.1387A>G mutations in FKRP. Muscle biopsies were reviewed and used for histopathology, immunostaining, Western blotting, and DNA extraction. Genetic analysis was performed on extracted DNA.

Results

We report the clinical phenotypes of 6 patients homozygous for the c.1387A>G mutation in FKRP. Onset of symptoms was <2 years, and 5 of the 6 patients never learned to walk. Brain MRIs were normal. Cognition was normal to mildly impaired. Microarray analysis of 5 homozygous FKRP c.1387A>G patients revealed a 500-kb region of shared homozygosity at 19q13.32, including FKRP. All 4 muscle biopsies available for review showed end-stage dystrophic pathology, near absence of glycosylated α-dystroglycan (α-DG) by immunofluorescence, and reduced molecular weight of α-DG compared with controls and patients with homozygous FKRP c.826C>A limb-girdle muscular dystrophy.

Conclusions

The clinical features and muscle pathology in these newly reported patients homozygous for FKRP c.1387A>G confirm that this mutation causes congenital muscular dystrophy. The clinical severity might be explained by the greater reduction in α-DG glycosylation compared with that seen with the c.826C>A mutation. The shared region of homozygosity at 19q13.32 indicates that FKRP c.1387A>G is a founder mutation with an estimated age of 60 generations (∼1,200–1,500 years).

Challenges of implementing a personalized mental task near-infrared spectroscopy brain-computer interface for a non-verbal young adult with motor impairments

PURPOSE

Near-infrared spectroscopy brain-computer interfaces (NIRS-BCIs) have been proposed as potential motor-free communication pathways. This paper documents the challenges of implementing an NIRS-BCI with a non-verbal, severely and congenitally impaired, but cognitively intact young adult.

METHODS

A 5-session personalized mental task NIRS-BCI training paradigm was invoked, whereby participant-specific mental tasks were selected either by the researcher or by the user, on the basis of prior performance or user preference.

RESULTS

Although the personalized mental task selection and training framework had been previously demonstrated with able-bodied participants, the participant was not able to exceed chance-level accuracies. Challenges to the acquisition of BCI control may have included disinclination to BCI training, structural or functional brain atypicalities, heightened emotional arousal and confounding haemodynamic patterns associated with novelty and reward processing.

CONCLUSIONS

Overall, we stress the necessity for further clinical NIRS-BCI research involving non-verbal individuals with severe motor impairments.

Comparison of brain MRI findings with language and motor function in the dystroglycanopathies

OBJECTIVE

To describe the spectrum of brain MRI findings in a cohort of individuals with dystroglycanopathies (DGs) and relate MRI results to function.

METHODS

All available brain MRIs done for clinical indications on individuals enrolled in a DG natural history study (NCT00313677) were reviewed. Reports were reviewed when MRI was not available. MRIs were categorized as follows: (1) cortical, brainstem, and cerebellar malformations; (2) cortical and cerebellar malformations; or (3) normal. Language development was assigned to 1 of 3 categories by a speech pathologist. Maximal motor function and presence of epilepsy were determined by history or examination.

RESULTS

Twenty-five MRIs and 9 reports were reviewed. The most common MRI abnormalities were cobblestone cortex or dysgyria with an anterior-posterior gradient and cerebellar hypoplasia. Seven individuals had MRIs in group 1, 8 in group 2, and 19 in group 3. Language was impaired in 100% of those in MRI groups 1 and 2, and degree of language impairment correlated with severity of imaging. Eighty-five percent of the whole group achieved independent walking, but only 33% did in group 1. Epilepsy was present in 8% of the cohort and rose to 37% of those with an abnormal MRI.

CONCLUSIONS

Developmental abnormalities of the brain such as cobblestone lissencephaly, cerebellar cysts, pontine hypoplasia, and brainstem bowing are hallmarks of DG and should prompt consideration of these diagnoses. Brain imaging in individuals with DG helps to predict outcomes, especially language development, aiding clinicians in prognostic counseling.

FKRP mutations, including a founder mutation, cause phenotype variability in Chinese patients with dystroglycanopathies

Mutations in the fukutin-related protein (FKRP) gene have been associated with dystroglycanopathies, which are common in Europe but rare in Asia. Our study aimed to retrospectively analyze and characterize the clinical, myopathological and genetic features of 12 Chinese patients with FKRP mutations. Three patients were diagnosed with congenital muscular dystrophy type 1C (MDC1C) and nine patients were diagnosed with limb girdle muscular dystrophy type 2I (LGMD2I). Three muscle biopsy specimens had dystrophic changes and reduced glycosylated α-dystroglycan staining, and two showed reduced expression of laminin α2. Two known and 13 novel mutations were identified in our single center cohort. Interestingly, the c.545A>G mutation was found in eight of the nine LGMD2I patients as a founder mutation and this founder mutation in Chinese patients differs from the one seen in European patients. Moreover, patients homozygous for the c.545A>G mutation were clinically asymptomatic, a less severe phenotype than in compound heterozygous patients with the c.545A>G mutation. The 13 novel mutations of FKRP significantly expanded the mutation spectrum of MDC1C and LGMD2I, and the different founder mutations indicate the ethnic difference in FKRP mutations.

Identification of a Post-translational Modification with Ribitol-Phosphate and Its Defect in Muscular Dystrophy

Glycosylation is an essential post-translational modification that underlies many biological processes and diseases. α-dystroglycan (α-DG) is a receptor for matrix and synaptic proteins that causes muscular dystrophy and lissencephaly upon its abnormal glycosylation (α-dystroglycanopathies). Here we identify the glycan unit ribitol 5-phosphate (Rbo5P), a phosphoric ester of pentose alcohol, in α-DG. Rbo5P forms a tandem repeat and functions as a scaffold for the formation of the ligand-binding moiety. We show that enzyme activities of three major α-dystroglycanopathy-causing proteins are involved in the synthesis of tandem Rbo5P. Isoprenoid synthase domain-containing (ISPD) is cytidine diphosphate ribitol (CDP-Rbo) synthase. Fukutin and fukutin-related protein are sequentially acting Rbo5P transferases that use CDP-Rbo. Consequently, Rbo5P glycosylation is defective in α-dystroglycanopathy models. Supplementation of CDP-Rbo to ISPD-deficient cells restored α-DG glycosylation. These findings establish the molecular basis of mammalian Rbo5P glycosylation and provide insight into pathogenesis and therapeutic strategies in α-DG-associated diseases.

Diagnostic approach to the congenital muscular dystrophies

Congenital muscular dystrophies (CMDs) are early onset disorders of muscle with histological features suggesting a dystrophic process. The congenital muscular dystrophies as a group encompass great clinical and genetic heterogeneity so that achieving an accurate genetic diagnosis has become increasingly challenging, even in the age of next generation sequencing. In this document we review the diagnostic features, differential diagnostic considerations and available diagnostic tools for the various CMD subtypes and provide a systematic guide to the use of these resources for achieving an accurate molecular diagnosis. An International Committee on the Standard of Care for Congenital Muscular Dystrophies composed of experts on various aspects relevant to the CMDs performed a review of the available literature as well as of the unpublished expertise represented by the members of the committee and their contacts. This process was refined by two rounds of online surveys and followed by a three-day meeting at which the conclusions were presented and further refined. The combined consensus summarized in this document allows the physician to recognize the presence of a CMD in a child with weakness based on history, clinical examination, muscle biopsy results, and imaging. It will be helpful in suspecting a specific CMD subtype in order to prioritize testing to arrive at a final genetic diagnosis.

Congenital muscular dystrophies: a brief review

Congenital muscular dystrophies (CMDs) are clinically and genetically heterogeneous neuromuscular disorders with onset at birth or in infancy in which the muscle biopsy is compatible with a dystrophic myopathy. In the past 10 years, knowledge of neuromuscular disorders has dramatically increased, particularly with the exponential boost of disclosing the genetic background of CMDs. This review will highlight the clinical description of the most important forms of CMD, paying particular attention to the main keys for diagnostic approach. The diagnosis of CMDs requires the concurrence of expertise in multiple specialties (neurology, morphology, genetics, neuroradiology) available in a few centers worldwide that have achieved sufficient experience with the different CMD subtypes. Currently, molecular diagnosis is of paramount importance not only for phenotype-genotype correlations, genetic and prenatal counseling, and prognosis and aspects of management, but also concerning the imminent availability of clinical trials and treatments.

Cardiovascular magnetic resonance of cardiomyopathy in limb girdle muscular dystrophy 2B and 2I

BACKGROUND

Limb girdle muscular dystrophies (LGMD) are inclusive of 7 autosomal dominant and 14 autosomal recessive disorders featuring progressive muscle weakness and atrophy. Studies of cardiac function have not yet been well-defined in deficiencies of dysferlin (LGMD2B) and fukutin related protein (LGMD2I). In this study of patients with these two forms of limb girdle muscular dystrophy, cardiovascular magnetic resonance (CMR) was used to more specifically define markers of cardiomyopathy including systolic dysfunction, myocardial fibrosis, and diastolic dysfunction.

METHODS

Consecutive patients with genetically-proven LGMD types 2I (n = 7) and 2B (n = 9) and 8 control subjects were enrolled. All subjects underwent cardiac magnetic resonance (CMR) on a standard 1.5 Tesla clinical scanner with cine imaging for left ventricular (LV) volume and ejection fraction (EF) measurement, vector velocity analysis of cine data to calculate myocardial strain, and late post-gadolinium enhancement imaging (LGE) to assess for myocardial fibrosis.

RESULTS

Sixteen LGMD patients (7 LGMD2I, 9 LGMD2B), and 8 control subjects completed CMR. All but one patient had normal LV size and systolic function; one (type 2I) had severe dilated cardiomyopathy. Of 15 LGMD patients with normal systolic function, LGE imaging revealed focal myocardial fibrosis in 7 (47%). Peak systolic circumferential strain rates were similar in patients vs. controls: εendo was -23.8 ± 8.5vs. -23.9 ± 4.2%, εepi was -11.5 ± 1.7% vs. -10.1 ± 4.2% (p = NS for all). Five of 7 LGE-positive patients had grade I diastolic dysfunction [2I (n = 2), 2B (n = 3)]. that was not present in any LGE-negative patients or controls.

CONCLUSIONS

LGMD2I and LGMD2B generally result in mild structural and functional cardiac abnormalities, though severe dilated cardiomyopathy may occur. Long-term studies are warranted to evaluate the prognostic significance of subclinical fibrosis detected by CMR in these patients.

Cognitive profile and MRI findings in limb-girdle muscular dystrophy 2I

Limb-girdle muscular dystrophy 2I (LGMD2I) is a neuromuscular disorder with a heterogeneous phenotype. It is caused by mutations in the Fukutin Related Protein (FKRP) gene, which is ubiquitously expressed in human tissues. FKRP functions in CNS are largely unknown. To investigate possible cognitive impairment in LGMD2I and to describe brain MRI features. Ten LGMD2I patients (four males and six females, mean age 44 years, age range 19-69 years) were assessed with an extensive neuropsychological battery, psychopathological tests and neuromuscular specific quality-of-life questionnaire. Adults were compared with ten matched healthy controls. All patients underwent complete neurological examination, and nine underwent brain MRI scanning. Patients showed a fairly specific cognitive profile with mild impairment in executive functions and visuo-spatial planning without substantial impairment in global and logic IQ. MRI findings were heterogeneous: four patients showed non-specific white matter abnormalities; two patients showed moderate ventriculomegaly; three patients showed mild enlargement of subarachnoid spaces, without a specific pattern. Cerebellar atrophy was marked in one patient. Abnormal glycosylation of α-dystroglycan in LGMD2I may interfere with brain development and cognitive performances involving the frontal and posterior parietal regions, but does not result in specific brain MRI abnormalities.

A homozygous FKRP start codon mutation is associated with Walker-Warburg syndrome, the severe end of the clinical spectrum

Dystroglycanopathies are a heterogeneous group of disorders caused by defects in the glycosylation pathway of alpha-dystroglycan. The clinical spectrum ranges from severe congenital muscular dystrophy with structural brain and eye involvement to a relatively mild adult onset limb-girdle muscular dystrophy without brain abnormalities and normal intelligence. Mutations have been identified in one of six putative or demonstrated glycosyltransferases. Many different FKRP mutations have been identified, which cover the complete clinical spectrum of dystroglycanopathies. In contrast to the other known genes involved in these disorders, genotype-phenotype correlations are not obvious for FKRP mutations. To date, no homozygous or compound heterozygous null mutations have been identified in FKRP, suggesting that null mutations in FKRP could result in embryonic lethality. We report a family with two siblings carrying a homozygous mutation in the start codon of FKRP that is likely to result in a loss of functional FKRP protein. The clinical phenotype of the patients was consistent with Walker-Warburg syndrome, the most severe disorder in the disease spectrum of dystroglycanopathies.

Four Caucasian patients with mutations in the fukutin gene and variable clinical phenotype

Fukuyama congenital muscular dystrophy (FCMD) is frequent in Japan, due to a founder mutation of the fukutin gene (FKTN). Outside Japan, FKTN mutations have only been reported in a few patients with a wide spectrum of phenotypes from Walker-Warburg syndrome to limb-girdle muscular dystrophy (LGMD2M). We studied four new Caucasian patients from three unrelated families. All showed raised serum CK initially isolated in one case and muscular dystrophy. Immunohistochemical studies and haplotype analysis led us to search for mutations in FKTN. Two patients (two sisters) presented with congenital muscular dystrophy, mental retardation, and posterior fossa malformation including cysts, and brain atrophy at Brain MRI. The other two patients had normal intelligence and brain MRI. Sequencing of the FKTN gene identified three previously described mutations and two novel missense mutations. Outside Japan, fukutinopathies are associated with a large spectrum of phenotypes from isolated hyperCKaemia to severe CMD, showing a clear overlap with that of FKRP.

Muscle protein alterations in LGMD2I patients with different mutations in the Fukutin-related protein gene

Fukutin-related protein (FKRP) is a protein involved in the glycosylation of cell surface molecules. Pathogenic mutations in the FKRP gene cause both the more severe congenital muscular dystrophy Type 1C and the milder Limb-Girdle Type 2I form (LGMD2I). Here we report muscle histological alterations and the analysis of 11 muscle proteins: dystrophin, four sarcoglycans, calpain 3, dysferlin, telethonin, collagen VI, alpha-DG, and alpha2-laminin, in muscle biopsies from 13 unrelated LGMD2I patients with 10 different FKRP mutations. In all, a typical dystrophic pattern was observed. In eight patients, a high frequency of rimmed vacuoles was also found. A variable degree of alpha2-laminin deficiency was detected in 12 patients through immunofluorescence analysis, and 10 patients presented alpha-DG deficiency on sarcolemmal membranes. Additionally, through Western blot analysis, deficiency of calpain 3 and dystrophin bands was found in four and two patients, respectively. All the remaining proteins showed a similar pattern to normal controls. These results suggest that, in our population of LGMD2I patients, different mutations in the FKRP gene are associated with several secondary muscle protein reductions, and the deficiencies of alpha2-laminin and alpha-DG on sections are prevalent, independently of mutation type or clinical severity.

Protein O-mannosyltransferase activities in lymphoblasts from patients with α-dystroglycanopathies

Defects in O-mannosylation of alpha-dystroglycan cause some forms of congenital muscular dystrophy (CMD), the so-called alpha-dystroglycanopathies. Six genes are responsible for these diseases with overlapping phenotypes. We investigated the usefulness of a biochemical approach for the diagnosis and investigation of the alpha-dystroglycanopathies using immortalized lymphoblasts prepared from genetically diagnosed and undiagnosed CMD patients and from control subjects. We measured the activities of protein O-mannose beta1,2-N-acetylglucosaminyltransferase 1 (POMGnT1) and protein O-mannosyltransferase (POMT). Lymphoblasts from patients harbouring known mutations in either POMGNT1 or POMT1 showed a marked decrease in POMGnT1 or POMT activity, respectively, compared to controls. Furthermore, we identified pathogenic mutations in POMGNT1, POMT1 or POMT2 in six previously genetically uncharacterised patients who had very low enzyme activity. In conclusion, the lymphoblast-based enzymatic assay is a sensitive and useful method (i) to select patients harbouring POMGNT1, POMT1 or POMT2 mutations; (ii) to assess the pathogenicity of new or already described mutations.

Prenatal diagnosis of complete trisomy 19q

This communication presents the first case of complete trisomy 19q, prenatally detected by ultrasound investigation. Real-time high-resolution ultrasound examination was performed at 19 weeks of gestation. After termination of the pregnancy, autopsy investigation was done. GTG-banding, fluorescence in situ hybridization m-(FISH) analysis, and FISH analysis with a 19q subtelomeric specific probe were used for identification of the fetal karyotype. Sonographic examination revealed an enlarged cisterna magna, cerebellar hypoplasia and aplasia of the inferior part of the vermis, combined and bilateral kidney malformations, significant nuchal fold, absence of fetal nasal bones, and intracardial calcifications. Autopsy confirmed ultrasound findings, but also revealed situs viscerum inversus of the lungs. Fetal karyotype was defined as: 46,XY,der(21)t(19;21)(q11;p13)mat. Our ultrasound and autopsy findings will certainly contribute to better knowledge of phenotype characterization of this rare chromosomal disorder.

MRI findings in congenital muscular dystrophies associated with brain abnormalities

Magnetic resonance imaging (MRI) has become an important tool in diagnosing complex congenital muscular dystrophies (CMD) with brain abnormalities. Currently, there are two recognized types of CMDs with MRI brain abnormalities, firstly, laminin α2-chain-deficient CMD (MDC1A) with mutations in the LAMA2 gene, and secondly CMDs with hypoglycosylated α-dystroglycan which include Walker–Warburg syndrome (WWS), muscle–eye–brain disease (MEB), Fukuyama CMD (FCMD) and CMD types 1C and 1D (MDC1C and 1D). Brain MRI in MDC1A demonstrates abnormal white matter but rarely other brain abnormalities. In the latter group of CMDs, there is a whole spectrum of abnormalities involving both white and gray matter. The most severe MRI findings are in WWS. Patients with MEB, FCMD and MDC1C and lD also have gray and white matter abnormalities, which, in general, are less severe than those observed in WWS. There may be an overlap in these complex CMDs, both genotypically and in MRI findings.