Search

Muscle magnetic resonance imaging (MRI) and ultrasound (US) are emerging tools to assist in the diagnosis of children with genetic muscle disease. Increasing number of studies demonstrate that these imaging techniques can identify selective patterns of muscle atrophy, fatty degeneration, and muscle edema that help to distinguish between different early-onset genetic myopathies and muscular dystrophies. Recognizing patterns of pathology by muscle imaging can help to guide genetic testing and avoid the more invasive procedure of a muscle biopsy. Conversely, since massive parallel sequencing is now more commonly used as the initial step in diagnostic testing, imaging techniques can help to confirm or exclude if a variant of uncertain significance is indeed disease causing and compatible with a pattern of pathology as detected by muscle imaging. Whereas for diagnostic purposes and pattern recognition, muscle pathology does not need to be quantified, measuring disease progression is increasingly supported by quantitative muscle imaging, which is critical given the recent increment in rare disease therapeutic trials. Here, we discuss the value of muscle imaging techniques in pediatricmuscle disease and summarize data identifying specific patterns of involvement in muscle MRI and US in some of the more common genetic myopathies and muscular dystrophies. [ABSTRACT FROM AUTHOR]

Background Despite remarkable advances in genetic testing, many adults with syndromic epilepsy remain without a molecular diagnosis. The challenge in providing genetic testing for this patient population lies in the extensive genetic heterogeneity associated with epilepsy. Even for the subset of epilepsy patients that present with a defining feature, such as microcephaly, the number of possible genes that would require interrogation by Sanger sequencing is extensive and often prohibitively expensive. Case presentation We report a family of French Canadian descent with four adult children affected with severe intellectual disability, epilepsy and microcephaly born to consanguineous parents and evaluated by the Genetics Service to provide informed genetic counseling to unaffected family members regarding possible recurrence risks. We used whole-exome sequencing (WES) of DNA from one affected sibling as a first-line diagnostic tool and compared the prioritization of variants using two strategies: 1) focusing on genes with homozygous variants; and, 2) focusing on genes associated with microcephaly. Both approaches prioritized the same homozygous novel frameshift mutation (p.Arg608Serfs"26) in WDR62, a gene known to cause autosomal recessive primary microcephaly. Sanger sequencing confirmed the presence of the homozygous mutation in the other three affected siblings. Conclusions WES and subsequent filtering of the rare variants in a single affected family member led to the rapid and cost-effective identification of a novel homozygous frameshift mutation in WDR62, thereby explaining the severe neurodevelopmental disorder in this family and facilitating genetic counseling. Our findings support WES as an effective first-line diagnostic tool in families presenting with rare genetically heterogeneous neurological disorders. [ABSTRACT FROM AUTHOR]

ABSTRACT Ataxia demonstrates substantial phenotypic and genetic heterogeneity. We set out to determine the diagnostic yield of exome sequencing in pediatric patients with ataxia without a molecular diagnosis after standard-of-care assessment in Canada. FORGE (Finding Of Rare disease GEnes) Canada is a nation-wide project focused on identifying novel disease genes for rare pediatric diseases using whole-exome sequencing. We retrospectively selected all FORGE Canada projects that included cerebellar ataxia as a feature. We identified 28 such families and a molecular diagnosis was made in 13; a success rate of 46%. In 11 families, we identified mutations in genes associated with known neurological syndromes and in two we identified novel disease genes. Exome analysis of sib pairs and/or patients born to consanguineous parents was more likely to be successful (9/13) than simplex cases (4/15). Our data suggest that exome sequencing is an effective first line test for pediatric patients with ataxia where a specific single gene is not immediately suspected to be causative. [ABSTRACT FROM AUTHOR]

In 1987 Fitzsimmons and Guilbert described identical male twins with progressive spastic paraplegia, brachydactyly with cone shaped epiphyses, short stature, dysarthria, and "low-normal" intelligence. In subsequent years, four other patients, including one set of female identical twins, a single female child, and a single male individual were described with the same features, and the eponym Fitzsimmons syndrome was adopted (OMIM #270710). We performed exome analysis of the patient described in 2009, and one of the original twins from 1987, the only patients available from the literature. No single genetic etiology exists that explains Fitzsimmons syndrome; however, multiple different genetic causes were identified. Specifically, the twins described by Fitzsimmons had heterozygous mutations in the SACS gene, the gene responsible for autosomal recessive spastic ataxia of Charlevoix Saguenay (ARSACS), as well as a heterozygous mutation in the TRPS1, the gene responsible in Trichorhinophalangeal syndrome type 1 (TRPS1 type 1) which includes brachydactyly as a feature. A TBL1XR1 mutation was identified in the patient described in 2009 as contributing to his cognitive impairment and autistic features with no genetic cause identified for his spasticity or brachydactyly. The findings show that these individuals have multiple different etiologies giving rise to a similar phenotype, and that "Fitzsimmons syndrome" is in fact not one single syndrome. Over time, we anticipate that continued careful phenotyping with concomitant genome-wide analysis will continue to identify the causes of many rare syndromes, but it will also highlight that previously delineated clinical entities are, in fact, not syndromes at all. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Background: Congenital nonprogressive spinocerebellar ataxia is characterized by early gross motor delay, hypotonia, gait ataxia, mild dysarthria and dysmetria. The clinical presentation remains fairly stable and may be associated with cerebellar atrophy. To date, only a few families with autosomal dominant congenital nonprogressive spinocerebellar ataxia have been reported. Linkage to 3pter was demonstrated in one large Australian family and this locus was designated spinocerebellar ataxia type 29. The objective of this study is to describe an unreported Canadian family with autosomal dominant congenital nonprogressive spinocerebellar ataxia and to identify the underlying genetic causes in this family and the original Australian family., Methods and Results: Exome sequencing was performed for the Australian family, resulting in the identification of a heterozygous mutation in the ITPR1 gene. For the Canadian family, genotyping with microsatellite markers and Sanger sequencing of ITPR1 gene were performed; a heterozygous missense mutation in ITPR1 was identified., Conclusions: ITPR1 encodes inositol 1,4,5-trisphosphate receptor, type 1, a ligand-gated ion channel that mediates calcium release from the endoplasmic reticulum. Deletions of ITPR1 are known to cause spinocerebellar ataxia type 15, a distinct and very slowly progressive form of cerebellar ataxia with onset in adulthood. Our study demonstrates for the first time that, in addition to spinocerebellar ataxia type 15, alteration of ITPR1 function can cause a distinct congenital nonprogressive ataxia; highlighting important clinical heterogeneity associated with the ITPR1 gene and a significant role of the ITPR1-related pathway in the development and maintenance of the normal functions of the cerebellum.