Kathryn Selby

An analysis of exome sequencing for diagnostic testing of the genes associated with muscle disease and spastic paraplegia.

In this study, we assess exome sequencing (ES) as a diagnostic alternative for genetically heterogeneous disorders. Because ES readily identified a previously reported homozygous mutation in the CAPN3 gene for an individual with an undiagnosed limb girdle muscular dystrophy, we evaluated ES as a generalizable clinical diagnostic tool by assessing the targeting efficiency and sequencing coverage of 88 genes associated with muscle disease (MD) and spastic paraplegia (SPG). We used three exome‐capture kits on 125 individuals. Exons constituting each gene were defined using the UCSC and CCDS databases. The three exome‐capture kits targeted 47–92% of bases within the UCSC‐defined exons and 97–99% of bases within the CCDS‐defined exons. An average of 61.2–99.5% and 19.1–99.5% of targeted bases per gene were sequenced to 20X coverage within the CCDS‐defined MD and SPG coding exons, respectively. Greater than 95–99% of targeted known mutation positions were sequenced to ≥1X coverage and 55–87% to ≥20X coverage in every exome. We conclude, therefore, that ES is a rapid and efficient first‐tier method to screen for mutations, particularly within the CCDS annotated exons, although its application requires disclosure of the extent of coverage for each targeted gene and supplementation with second‐tier Sanger sequencing for full coverage. Hum Mutat 33:614–626, 2012.

Myostatin inhibitor ACE‐031 treatment of ambulatory boys with Duchenne muscular dystrophy: Results of a randomized, placebo‐controlled clinical trial

Introduction: ACE‐031 is a fusion protein of activin receptor type IIB and IgG1‐Fc, which binds myostatin and related ligands. It aims to disrupt the inhibitory effect on muscle development and provide potential therapy for myopathies like Duchenne muscular dystrophy (DMD). Methods: ACE‐031 was administered subcutaneously every 2–4 weeks to DMD boys in a randomized, double‐blind, placebo‐controlled, ascending‐dose trial. The primary objective was safety evaluation. Secondary objectives included characterization of pharmacokinetics and pharmacodynamics. Results: ACE‐031 was not associated with serious or severe adverse events. The study was stopped after the second dosing regimen due to potential safety concerns of epistaxis and telangiectasias. A trend for maintenance of the 6‐minute walk test (6MWT) distance in the ACE‐031 groups compared with a decline in the placebo group (not statistically significant) was noted, as was a trend for increased lean body mass and bone mineral density (BMD) and reduced fat mass. Conclusion: ACE‐031 use demonstrated trends for pharmacodynamic effects on lean mass, fat mass, BMD, and 6MWT. Non–muscle‐related adverse events contributed to the decision to discontinue the study. Myostatin inhibition is a promising therapeutic approach for DMD. Muscle Nerve 55: 458–464, 2017

A population-based study of dystrophin mutations in Canada.

INTRODUCTION We carried out a population-based study of dystrophin mutations in patients followed by members of the Canadian Paediatric Neuromuscular Group (CPNG) over a ten-year period. OBJECTIVES We aimed to describe the changes in diagnostic testing for dystrophinopathy and to determine the frequency of dystrophin mutations from 2000 to 2009. METHODS De-identified data containing the clinical phenotypes, diagnostic methods, and mutational reports from dystrophinopathy patients followed by CPNG centres from January 2000 to December 2009 were analyzed using descriptive statistics. RESULTS 773 patients had a confirmed diagnosis of dystrophinopathy based on genetic testing (97%), muscle biopsy (2%), or family history (1%). 573 (74%) had complete deletion/duplication analysis of all 79 exons or whole gene sequencing, resulting in 366 (64%) deletions, 64 (11%) duplications, and 143 (25%) point mutations. The percentage of patients who were diagnosed using currently accepted genetic testing methods varied across Canada, with a mean of 63% (SD 23). 246 (43%) mutations involved exons 45 to 53. The top ten deletions (n=147, 26%) were exons 45-47, 45-48, 45, 45-50, 45-55, 51, 45-49, 45-52, 49-50, and 46-47. 169 (29%) mutations involved exons 2 to 20. The most common duplications (n=29, 5.1%) were exons 2, 2-7, 2-17, 3-7, 8-11, 10, 10-11, and 12. CONCLUSION This is the most comprehensive report of dystrophin mutations in Canada. Consensus guidelines regarding the diagnostic approach to dystrophinopathy will hopefully reduce the geographical variation in mutation detection rates in the coming decade.

Hemiplegic migraine, seizures, progressive spastic paraparesis, mood disorder, and coma in siblings with low systemic serotonin

Background: Serotonin has an important role in vascular resistance and blood pressure control, and a functional serotonin transporter polymorphism has been associated with migraine. Disturbances in serotonin metabolism have been associated with autism, depression, and myoclonus related conditions, but serotonin has far more functions in the body. Familial hemiplegic migraine is a rare autosomal dominant subtype of migraine with aura in which attacks are associated with hemiparesis. Cases: We present two siblings with hemiplegic migraine, depression, progressive spastic paraparesis, myelopathy, and spinal cord atrophy. One of the sisters presented with prolonged coma after a migraine episode. Both sisters were found to have low cerebrospinal fluid serotonin metabolite (5-hydroxyindoleacetic acid), low platelet serotonin levels, and diminished serotonin transport capacity. Their clinical symptoms improved on 5-hydroxytryptophan replacement therapy. Mutational analysis of the CACNA1A and ATP1A2 genes was negative. Conclusion: This is the first time that systemic serotonin deficiency has been described in familial hemiplegic migraine. We hypothesize that the deficiency of serotonin transport may be part of a complex cellular membrane trafficking dysfunction involving not only the serotonin transporter but also other transporters and ion channels.

Brain MRI abnormalities and spectrum of neurological and clinical findings in three patients with proximal 16p11.2 microduplication

The phenotype of recurrent ∼600 kb microdeletion and microduplication on proximal 16p11.2 is characterized by a spectrum of neurodevelopmental impairments including developmental delay and intellectual disability, epilepsy, autism and psychiatric disorders which are all subject to incomplete penetrance and variable expressivity. A variety of brain MRI abnormalities were reported in patients with 16p11.2 rearrangements, but no systematic correlation has been studied among patients with similar brain anomalies, their neurodevelopmental and clinical phenotypes. We present three patients with the proximal 16p11.2 microduplication exhibiting significant developmental delay, anxiety disorder and other variable clinical features. Our patients have abnormal brain MRI findings of cerebral T2 hyperintense foci (3/3) and ventriculomegaly (2/3). The neuroradiological or neurological findings in two cases prompted an extensive diagnostic work‐up. One patient has exhibited neurological regression and progressive vision impairment and was diagnosed with juvenile neuronal ceroid‐lipofuscinosis. We compare the clinical course and phenotype of these patients in regard to the clinical significance of the cerebral lesions and the need for MRI surveillance. We conclude that in all three patients the lesions were not progressive, did not show any sign of malignant transformation and could not be correlated to specific clinical features. We discuss potential etiologic mechanisms that may include overexpression of genes within the duplicated region involved in control of cell proliferation and complex molecular mechanisms such as the MAPK/ERK pathway. Systematic studies in larger cohorts are needed to confirm our observation and to establish the prevalence and clinical significance of these neuroanatomical abnormalities in patients with 16p11.2 duplications.

Longitudinal Outcomes in the 2014 Acute Flaccid Paralysis Cluster in Canada: A Nationwide Study

We describe the presenting features and long-term outcome of an unusual cluster of pediatric acute flaccid paralysis cases that occurred in Canada during the 2014 enterovirus D68 outbreak. Children (n = 25; median age 7.8 years) presenting to Canadian centers between July 1 and October 31, 2014, and who met diagnostic criteria for acute flaccid paralysis were evaluated retrospectively. The predominant presenting features included prodromal respiratory illness (n = 22), cerebrospinal fluid lymphocytic pleocytosis (n = 18), pain in neck/back (n = 14) and extremities (n = 10), bowel/bladder dysfunction (n = 9), focal central gray matter lesions found in all regions of the spinal cord within the cohort (n = 16), brain stem lesions (n = 8), and bulbar symptoms (n = 5). Enterovirus D68 was detectable in nasopharyngeal specimens (n = 7) but not in cerebrospinal fluid. Acute therapies (corticosteroids, intravenous immunoglobulins, plasmapheresis) were well tolerated with few side effects. Fourteen of 16 patients who were followed beyond 12 months post onset had neurologic deficits but showed ongoing clinical improvement and motor recovery.

Compound heterozygous TRPV4 mutations in two siblings with a complex phenotype including severe intellectual disability and neuropathy

TRPV4 encodes a polymodal calcium‐permeable plasma membrane channel. Dominant pathogenic mutations in TRPV4 lead to a wide spectrum of abnormal phenotypes. This is the first report of biallelic TRPV4 mutations and we describe two compound heterozygous siblings presenting with a complex phenotype including severe neuromuscular involvement. In light of previously well described dominant inheritance for TRPV4‐related neuromuscular disease, our study suggests a role for compound heterozygosity and loss‐of‐function as a potential novel disease mechanism for this group of disorders. Profound intellectual disability was also noted in both affected children, suggesting that TRPV4 may be necessary for normal brain development.

The Canadian Neuromuscular Disease Registry: Connecting patients to national and international research opportunities

Introduction Patient registries serve an important role in rare disease research, particularly for the recruitment and planning of clinical trials. The Canadian Neuromuscular Disease Registry was established with the primary objective of improving the future for neuromuscular (NM) patients through the enablement and support of research into potential treatments. Methods In this report, we discuss design and utilization of the Canadian Neuromuscular Disease Registry with special reference to the paediatric cohort currently enrolled in the registry. Results As of July 25, 2017, there are 658 paediatric participants enrolled in the registry, 249 are dystrophinopathies (229 are Duchenne muscular dystrophy), 57 are myotonic dystrophy participants, 98 spinal muscular atrophy participants and 65 are limb girdle muscular dystrophy. A total of 175 patients have another NM diagnosis. The registry has facilitated 20 clinical trial inquiries, 5 mail-out survey studies and 5 other studies in the paediatric population. Discussion The strengths of the registry are discussed. The registry has proven to be an invaluable tool to NM disease research and has increased Canadas visibility as a competitive location for the conduct of clinical trials for NM therapies.

Improved strength on 5-hydroxytryptophan and carbidopa in spinal cord atrophy

There is ample evidence of an important role of descending serotonergic projections in modulating spinal motor neuron activation and firing, and experimental studies suggest that 5-HT receptor stimulation can improve motor function after spinal cord injury; however, relevant clinical data is sorely lacking. We describe two sisters with hemiplegic migraine, low CSF and platelet serotonin levels, and progressive spastic paraparesis associated with profound spinal cord atrophy whose lower extremity strength and ambulation responded to a precursor replacement strategy (5-hydroxytryptophan and carbidopa administration), an approach that may have broader applicability in myelopathies of diverse etiology where descending serotonergic projections are compromised.