Publications by authors named "Stacy Hewson"

24 Publications

  • Page 1 of 1

Extended Phenotyping and Functional Validation Facilitate Diagnosis of a Complex Patient Harboring Genetic Variants in and Causing Overlapping Phenotypes.

Genes (Basel) 2021 Aug 29;12(9). Epub 2021 Aug 29.

Department of Ophthalmology and Vision Sciences, Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.

Identifying multiple ultra-rare genetic syndromes with overlapping phenotypes is a diagnostic conundrum in clinical genetics. This study investigated the pathogenicity of a homozygous missense variant in ( NM_016194.4: c.920T > G (p. Leu307Arg); NM_006578.4: c.794T > G (p. Leu265Arg)) identified through exome sequencing in a female child who also had 3-methylcrotonyl-CoA carboxylase (3-MCC) deficiency (newborn screening positive) and hemoglobin E trait. The proband presented with early-onset intellectual disability, the severity of which was more in keeping with -related disorder than 3-MCC deficiency. She later developed bradycardia and cardiac arrest, and upon re-phenotyping showed cone photo-transduction recovery deficit, all known only to -related disorders. Patient-derived fibroblast assays showed preserved GNB5S expression, but bioluminescence resonance energy transfer assay showed abolished function of the variant reconstituted Gβ5S containing RGS complexes for deactivation of D2 dopamine receptor activity, confirming variant pathogenicity. This study highlights the need for precise phenotyping and functional assays to facilitate variant classification and clinical diagnosis in patients with complex medical conditions.
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http://dx.doi.org/10.3390/genes12091352DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8469011PMC
August 2021

The Phenotypic Spectrum of Tuberous Sclerosis Complex: A Canadian Cohort.

Child Neurol Open 2021 Jan-Dec;8:2329048X211012817. Epub 2021 May 4.

Epilepsy Program, Division of Neurology, Department of Pediatrics, The Hospital for Sick Children, Toronto, Ontario, Canada.

Objective: We aimed to further elucidate the phenotypic spectrum of Tuberous Sclerosis Complex (TSC) depending on genotype.

Methods: A retrospective review of patients seen in the TSC clinic at the Hospital for Sick Children was conducted and the frequency of TSC manifestations was compared based on genotype.

Results: Nineteen-patients had TSC1 mutations, 36 had TSC2 mutations and 11 had no mutation identified (NMI). Patients with TSC2 mutations had a higher frequency of early-onset epilepsy and more frequent systemic manifestations. The NMI group had milder neurologic and systemic manifestations. Our data did not demonstrate that intellectual disability and infantile spasms were more common in TSC2 mutations.

Conclusions: This is the first Canadian pediatric cohort exploring the genotype-phenotype relationship in TSC. We report that some manifestations are more frequent and severe in TSC2 mutations and that NMI may have a milder phenotype. Disease surveillance and counseling should continue regardless of genotype until this is better elucidated.
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http://dx.doi.org/10.1177/2329048X211012817DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8114745PMC
May 2021

Outcomes of patients with cobalamin C deficiency: A single center experience.

JIMD Rep 2021 Jan 8;57(1):102-114. Epub 2020 Nov 8.

Division of Clinical and Metabolic Genetics, Department of Pediatrics The Hospital for Sick Children Toronto Ontario Canada.

Biallelic variants in results in the combined methylmalonic aciduria and homocystinuria, called cobalamin (cbl) C (cblC) deficiency. We report 26 patients with cblC deficiency with their phenotypes, genotypes, biochemical parameters, and treatment outcomes, who were diagnosed and treated at our center. We divided all cblC patients into two groups: group 1: SX group: identified after manifestations of symptoms (n = 11) and group 2: NB group: identified during the asymptomatic period via newborn screening (NBS) or positive family history of cblC deficiency (n = 15). All patients in the SX group had global developmental delay and/or cognitive dysfunction at the time of the diagnosis and at the last assessment. Seizure, stroke, retinopathy, anemia, cerebral atrophy, and thin corpus callosum in brain magnetic resonance imaging (MRI) were common in patients in the SX group. Global developmental delay and cognitive dysfunction was present in nine patients in the NB group at the last assessment. Retinopathy, anemia, and cerebral atrophy and thin corpus callosum in brain MRI were less frequent. We report favorable outcomes in patients identified in the neonatal period and treated pre-symptomatically. Identification of cblC deficiency by NBS is crucial to improve neurodevelopmental outcomes.
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http://dx.doi.org/10.1002/jmd2.12179DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7802631PMC
January 2021

A pathogenic UFSP2 variant in an autosomal recessive form of pediatric neurodevelopmental anomalies and epilepsy.

Genet Med 2021 05 20;23(5):900-908. Epub 2021 Jan 20.

Children's Medical Center Research Institute, UT Southwestern Medical Center, Dallas, TX, USA.

Purpose: Neurodevelopmental disabilities are common and genetically heterogeneous. We identified a homozygous variant in the gene encoding UFM1-specific peptidase 2 (UFSP2), which participates in the UFMylation pathway of protein modification. UFSP2 variants are implicated in autosomal dominant skeletal dysplasias, but not neurodevelopmental disorders. Homozygosity for the variant occurred in eight children from four South Asian families with neurodevelopmental delay and epilepsy. We describe the clinical consequences of this variant and its effect on UFMylation.

Methods: Exome sequencing was used to detect potentially pathogenic variants and identify shared regions of homozygosity. Immunoblotting assessed protein expression and post-translational modifications in patient-derived fibroblasts.

Results: The variant (c.344T>A; p.V115E) is rare and alters a conserved residue in UFSP2. Immunoblotting in patient-derived fibroblasts revealed reduced UFSP2 abundance and increased abundance of UFMylated targets, indicating the variant may impair de-UFMylation rather than UFMylation. Reconstituting patient-derived fibroblasts with wild-type UFSP2 reduced UFMylation marks. Analysis of UFSP2's structure indicated that variants observed in skeletal disorders localize to the catalytic domain, whereas V115 resides in an N-terminal domain possibly involved in substrate binding.

Conclusion: Different UFSP2 variants cause markedly different diseases, with homozygosity for V115E causing a severe syndrome of neurodevelopmental disability and epilepsy.
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http://dx.doi.org/10.1038/s41436-020-01071-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8105169PMC
May 2021

A Cross-Sectional Study of Nemaline Myopathy.

Neurology 2021 03 4;96(10):e1425-e1436. Epub 2021 Jan 4.

From the Division of Neurology (K.A.), Genetics and Genome Biology (K.A., M.A., J.J.D., M.B., N.S.), Division of Respiratory Medicine (R.A., F.S., T.T.), Centre for Computational Medicine (M.B., N.S.), Division of Emergency Medicine (M.D.), and Division of Clinical and Metabolic Genetics (S.H.), Hospital for Sick Children; Princess Margaret Hospital (S.S.), Department of Medical Oncology and Hematology; University of Toronto (R.A.), Ontario, Canada; The Manton Center for Orphan Disease Research (A.H.B., C.A.G.), Division of Genetics and Genomics, Boston Children's Hospital, Harvard Medical School, MA; National Institute of Neurological Disorders and Stroke (C.G.B.), Neuromuscular and Neurogenetic Disorders of Childhood Section, and Clinical Research Center (M.S.J.), Rehabilitation Medicine Department, NIH, Bethesda, MD; Department of Computer Science (M.B., M.G., N.S.), University of Toronto, Ontario, Canada; Columbia University Irving Medical Center (A.C.), Division of Pediatric Pulmonology, New York, NY; Goryeb Children's Hospital (J.D.), Department of Pediatric Neurology, Morristown, NJ; Mount Sinai Hospital (C.H.), Prenatal Diagnosis and Medical Genetics, Toronto, Ontario, Canada; Medical College of Wisconsin (M.W.L.), Department of Pathology and Laboratory Medicine, Milwaukee; Children's Hospital of Philadelphia (O.H.M.), Division of Pulmonology, PA; UT Southwestern Medical Center (L.N.), Department of Physical Therapy, Dallas, TX; and Driscoll Children's Hospital (C.H.W.), Division of Neurology, Texas A&M University, Corpus Christi.

Objective: Nemaline myopathy (NM) is a rare neuromuscular condition with clinical and genetic heterogeneity. To establish disease natural history, we performed a cross-sectional study of NM, complemented by longitudinal assessment and exploration of pilot outcome measures.

Methods: Fifty-seven individuals with NM were recruited at 2 family workshops, including 16 examined at both time points. Participants were evaluated by clinical history and physical examination. Functional outcome measures included the Motor Function Measure (MFM), pulmonary function tests (PFTs), myometry, goniometry, and bulbar assessments.

Results: The most common clinical classification was typical congenital (54%), whereas 42% had more severe presentations. Fifty-eight percent of individuals needed mechanical support, with 26% requiring wheelchair, tracheostomy, and feeding tube. The MFM scale was performed in 44 of 57 participants and showed reduced scores in most with little floor/ceiling effect. Of the 27 individuals completing PFTs, abnormal values were observed in 65%. Last, bulbar function was abnormal in all patients examined, as determined with a novel outcome measure. Genotypes included mutations in (18), (20), and (2). Seventeen individuals were genetically unresolved. Patients with pathogenic and variants were largely similar in clinical phenotype. Patients without genetic resolution had more severe disease.

Conclusion: We present a comprehensive cross-sectional study of NM. Our data identify significant disabilities and support a relatively stable disease course. We identify a need for further diagnostic investigation for the genetically unresolved group. MFM, PFTs, and the slurp test were identified as promising outcome measures for future clinical trials.
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http://dx.doi.org/10.1212/WNL.0000000000011458DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8055318PMC
March 2021

Homozygous GLUL deletion is embryonically viable and leads to glutamine synthetase deficiency.

Clin Genet 2020 12 1;98(6):613-619. Epub 2020 Oct 1.

Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, University of Toronto, Toronto, Canada.

Glutamine synthetase (GS) is the enzyme responsible for the biosynthesis of glutamine, providing the only source of endogenous glutamine necessary for several critical metabolic and developmental pathways. GS deficiency, caused by pathogenic variants in the glutamate-ammonia ligase (GLUL) gene, is a rare autosomal recessive inborn error of metabolism characterized by systemic glutamine deficiency, persistent moderate hyperammonemia, and clinically devastating seizures and multi-organ failure shortly after birth. The four cases reported thus far were caused by homozygous GLUL missense variants. We report a case of GS deficiency caused by homozygous GLUL gene deletion, diagnosed prenatally and likely representing the most severe end of the spectrum. We expand the known phenotype of this rare condition with novel dysmorphic, radiographic and neuropathologic features identified on post-mortem examination. The biallelic deletion identified in this case also included the RNASEL gene and was associated with immune dysfunction in the fetus. This case demonstrates that total absence of the GLUL gene in humans is viable beyond the embryonic period, despite the early embryonic lethality found in GLUL animal models.
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http://dx.doi.org/10.1111/cge.13844DOI Listing
December 2020

ALU transposition induces familial hypertrophic cardiomyopathy.

Mol Genet Genomic Med 2020 01 30;8(1):e951. Epub 2019 Sep 30.

CHEO, Ottawa, Canada.

Background: Hypertrophic cardiomyopathy (HCM) is characterized by left ventricular hypertrophy (LVH) in the absence of predisposing cardiovascular conditions. Pathogenic variants in at least 16 cardiac sarcomeric genes have been implicated in HCM, most of which act in a dominant-negative fashion. However loss-of-function (haploinsufficiency) is the most common disease mechanism for pathogenic variants in MYBPC3, suggesting that MYBPC3 complete deletion may play a role in HCM pathogenesis. Here, we investigate MYBPC3 complete deletion as a disease mechanism in HCM by analyzing two unrelated patients with confirmed diagnosis of HCM that tested negative by Sanger sequencing analysis.

Methods: MYBPC3 complete deletion was investigated by Multiplex ligation-dependent probe amplification (MLPA) and microarray analyses. The mechanism of deletion was investigated by interrogating the SINEBase database.

Results: Patient-1 was diagnosed with nonobstructive HCM in his mid-40s while undergoing assessment for palpitations, and patient-2 with obstructive HCM in his late-20s while undergoing systolic heart murmur assessment for an unrelated illness. MLPA testing revealed a heterozygous deletion of all MYBPC3 exons in both patients. Subsequent microarray testing confirmed these deletions which extended beyond the 5' and 3' ends of MYBPC3. Genomic assessment suggested that these deletions resulted from Alu/Alu-homologous recombination.

Conclusion: Our results demonstrate that haploinsufficiency resulting from MYBPC3 complete deletion, potentially mediated by Alu recombination, is an important disease mechanism in cardiomyopathy and emphasizes the importance of copy number variation analysis in patients clinically suspected of HCM.
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http://dx.doi.org/10.1002/mgg3.951DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6978237PMC
January 2020

Variants in TCF20 in neurodevelopmental disability: description of 27 new patients and review of literature.

Genet Med 2019 09 11;21(9):2036-2042. Epub 2019 Feb 11.

Spectrum Health Medical Genetics, Grand Rapids, MI, USA.

Purpose: To define the clinical characteristics of patients with variants in TCF20, we describe 27 patients, 26 of whom were identified via exome sequencing. We compare detailed clinical data with 17 previously reported patients.

Methods: Patients were ascertained through molecular testing laboratories performing exome sequencing (and other testing) with orthogonal confirmation; collaborating referring clinicians provided detailed clinical information.

Results: The cohort of 27 patients all had novel variants, and ranged in age from 2 to 68 years. All had developmental delay/intellectual disability. Autism spectrum disorders/autistic features were reported in 69%, attention disorders or hyperactivity in 67%, craniofacial features (no recognizable facial gestalt) in 67%, structural brain anomalies in 24%, and seizures in 12%. Additional features affecting various organ systems were described in 93%. In a majority of patients, we did not observe previously reported findings of postnatal overgrowth or craniosynostosis, in comparison with earlier reports.

Conclusion: We provide valuable data regarding the prognosis and clinical manifestations of patients with variants in TCF20.
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http://dx.doi.org/10.1038/s41436-019-0454-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7171701PMC
September 2019

Mitochondrial POLG related disorder presenting prenatally with fetal cerebellar growth arrest.

Metab Brain Dis 2018 08 25;33(4):1369-1373. Epub 2018 Mar 25.

Division of Clinical and Metabolic Genetics, Department of Paediatrics, The Hospital for Sick Children, University of Toronto, Toronto, ON, Canada.

We report the prenatal findings of severe cerebellar growth arrest in two siblings with POLG1 mutations. The first presented with seizures and lactic acidosis immediately after premature birth and was diagnosed with mitochondrial disease on muscle biopsy. Molecular DNA analysis confirmed homozygous missense mutation in the POLG1 gene. The pregnancy of the second sibling was monitored closely by repeat fetal ultrasounds since the parents declined invasive testing. A detailed fetal ultrasound at 19 weeks gestation showed a small cerebellum with transcerebellar diameter (TCD) on axial cranial imaging, measuring below the 5th centile for gestational age. Molecular analysis confirmed the same homozygous familial mutation in the POLG1gene. This report further delineates the phenotypic features of the POLG related disorders and expands it to the prenatal era. Subsequent pregnancies were monitored by molecular analysis, using chorionic villus sampling (CVS).
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http://dx.doi.org/10.1007/s11011-018-0218-2DOI Listing
August 2018

Periodic reanalysis of whole-genome sequencing data enhances the diagnostic advantage over standard clinical genetic testing.

Eur J Hum Genet 2018 05 16;26(5):740-744. Epub 2018 Feb 16.

Genome Diagnostics, Department of Paediatric Laboratory Medicine, The Hospital for Sick Children, Toronto, ON, Canada.

Whole-genome sequencing (WGS) as a first-tier diagnostic test could transform medical genetic assessments, but there are limited data regarding its clinical use. We previously showed that WGS could feasibly be deployed as a single molecular test capable of a higher diagnostic rate than current practices, in a prospectively recruited cohort of 100 children meeting criteria for chromosomal microarray analysis. In this study, we report on the added diagnostic yield with re-annotation and reanalysis of these WGS data ~2 years later. Explanatory variants have been discovered in seven (10.9%) of 64 previously undiagnosed cases, in emerging disease genes like HMGA2. No new genetic diagnoses were made by any other method in the interval period as part of ongoing clinical care. The results increase the cumulative diagnostic yield of WGS in the study cohort to 41%. This represents a greater than 5-fold increase over the chromosomal microarrays, and a greater than 3-fold increase over all the clinical genetic testing ordered in practice. These findings highlight periodic reanalysis as yet another advantage of genomic sequencing in heterogeneous disorders. We recommend reanalysis of an individual's genome-wide sequencing data every 1-2 years until diagnosis, or sooner if their phenotype evolves.
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http://dx.doi.org/10.1038/s41431-018-0114-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5945683PMC
May 2018

Prevalence of Genetic Disorders and GLUT1 Deficiency in a Ketogenic Diet Clinic.

Can J Neurol Sci 2018 01 16;45(1):93-96. Epub 2017 Nov 16.

1Department of Pediatrics,Division of Clinical and Metabolic Genetics,University of Toronto,Toronto,Ontario,Canada.

Between July of 2012 and December of 2014, 39 patients were enrolled prospectively to investigate the prevalence of glucose transporter 1 (GLUT1) deficiency in a ketogenic diet clinic. None of them had GLUT1 deficiency. All patients seen in the same clinic within the same period were reviewed retrospectively. A total of 18 of these 85 patients had a genetic diagnosis, including GLUT1 deficiency, pathogenic copy number variants, congenital disorder of glycosylation, neuronal ceroid lipofuscinosis type II, mitochondrial disorders, tuberous sclerosis, lissencephaly, and SCN1A-, SCN8A-, and STXBP1-associated epileptic encephalopathies. The prevalence of genetic diagnoses was 21% and prevalence of GLUT1 deficiency was 2.4% in our retrospective cohort study.
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http://dx.doi.org/10.1017/cjn.2017.246DOI Listing
January 2018

Improved diagnostic yield compared with targeted gene sequencing panels suggests a role for whole-genome sequencing as a first-tier genetic test.

Genet Med 2018 04 3;20(4):435-443. Epub 2017 Aug 3.

Division of Clinical and Metabolic Genetics, The Hospital for Sick Children, Toronto, Ontario, Canada.

PurposeGenetic testing is an integral diagnostic component of pediatric medicine. Standard of care is often a time-consuming stepwise approach involving chromosomal microarray analysis and targeted gene sequencing panels, which can be costly and inconclusive. Whole-genome sequencing (WGS) provides a comprehensive testing platform that has the potential to streamline genetic assessments, but there are limited comparative data to guide its clinical use.MethodsWe prospectively recruited 103 patients from pediatric non-genetic subspecialty clinics, each with a clinical phenotype suggestive of an underlying genetic disorder, and compared the diagnostic yield and coverage of WGS with those of conventional genetic testing.ResultsWGS identified diagnostic variants in 41% of individuals, representing a significant increase over conventional testing results (24%; P = 0.01). Genes clinically sequenced in the cohort (n = 1,226) were well covered by WGS, with a median exonic coverage of 40 × ±8 × (mean ±SD). All the molecular diagnoses made by conventional methods were captured by WGS. The 18 new diagnoses made with WGS included structural and non-exonic sequence variants not detectable with whole-exome sequencing, and confirmed recent disease associations with the genes PIGG, RNU4ATAC, TRIO, and UNC13A.ConclusionWGS as a primary clinical test provided a higher diagnostic yield than conventional genetic testing in a clinically heterogeneous cohort.
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http://dx.doi.org/10.1038/gim.2017.119DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5895460PMC
April 2018

Variable expressivity of a likely pathogenic variant in KCNQ2 in a three-generation pedigree presenting with intellectual disability with childhood onset seizures.

Am J Med Genet A 2017 Aug 11;173(8):2226-2230. Epub 2017 Jun 11.

Division of Clinical and Metabolic Genetics, Department of Pediatrics, University of Toronto, The Hospital for Sick Children, Toronto, Ontario, Canada.

KCNQ2 has been reported as a frequent cause of autosomal dominant benign familial neonatal seizures. De novo likely pathogenic variants in KCNQ2 have been described in neonatal or early infantile onset epileptic encephalopathy patients. Here, we report a three-generation family with six affected patients with a novel likely pathogenic variant (c.628C>T; p.Arg210Cys) in KCNQ2. Four family members, three adults and a child, presented with a childhood seizure onset with variability in the severity of seizures and response to treatment, intellectual disability (ID) as well as behavioral problems. The two youngest affected patients had a variable degree of global developmental delay with no seizures at their current age. This three-generation family with six affected members expands the phenotypic spectrum of KCNQ2 associated encephalopathy to KCNQ2 associated ID and or childhood onset epileptic encephalopathy. We think that KCNQ2 associated epileptic encephalopathy should be included in the differential diagnosis of childhood onset epilepsy and early onset global developmental delay, cognitive dysfunction, or ID. Furthermore, whole exome sequencing in families with ID and history of autosomal dominant inheritance pattern with or without seizures, may further broaden the phenotypic spectrum of KCNQ2 associated epileptic encephalopathy or encephalopathy.
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http://dx.doi.org/10.1002/ajmg.a.38281DOI Listing
August 2017

Novel recessive mutations in COQ4 cause severe infantile cardiomyopathy and encephalopathy associated with CoQ deficiency.

Mol Genet Metab Rep 2017 Sep 11;12:23-27. Epub 2017 May 11.

Division of Personalized Genomic Medicine, Department of Pathology and Cell Biology, Columbia University Medical Center, United States.

Coenzyme Q (CoQ) or ubiquinone is one of the two electron carriers in the mitochondrial respiratory chain which has an essential role in the process of oxidative phosphorylation. Defects in CoQ synthesis are usually associated with the impaired function of CoQ-dependent complexes I, II and III. The recessively transmitted CoQ deficiency has been associated with a number of phenotypically and genetically heterogeneous groups of disorders manifesting at variable age of onset. The infantile, multisystemic presentation is usually caused by mutations in genes directly involved in CoQ biosynthesis. To date, mutations in ( and ), , , , , /, , and genes have been identified in patients with primary form of CoQ deficiency. Here we report novel mutations in the gene, which were identified in an infant with profound mitochondrial disease presenting with perinatal seizures, hypertrophic cardiomyopathy and severe muscle CoQ deficiency.
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http://dx.doi.org/10.1016/j.ymgmr.2017.05.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5432661PMC
September 2017

Long-term outcome of patients with X-linked adrenoleukodystrophy: A retrospective cohort study.

Eur J Paediatr Neurol 2017 Jul 21;21(4):600-609. Epub 2017 Feb 21.

Division of Clinical and Metabolic Genetics, Department of Pediatrics, University of Toronto, The Hospital for Sick Children, Toronto, Canada; Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, Canada.

Background: X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal disorder associated with leukodystrophy, myeloneuropathy and adrenocortical insufficiency. We performed a retrospective cohort study to evaluate long-term outcome of patients with X-ALD.

Method: All patients with X-ALD diagnosed between 1989 and 2012 were included. Electronic patient charts were reviewed for clinical features, biochemical investigations, molecular genetic testing, neuroimaging, long-term outcome and treatment.

Results: Forty-eight patients from 18 unrelated families were included (15 females; 33 males). Seventeen patients were symptomatic at the time of the biochemical diagnosis including 14 with neurocognitive dysfunction and 3 with Addison disease only. Thirty-one asymptomatic individuals were identified by positive family history of X-ALD. During follow-up, eight individuals developed childhood cerebral X-ALD (CCALD), one individual developed adrenomyeloneuropathy (AMN), six individuals developed Addison disease only, and five individuals remained asymptomatic. Direct sequencing of ABCD1 confirmed the genetic diagnosis in 29 individuals. Seven patients with CCALD underwent hematopoietic stem cell transplantation (HSCT). Nine patients lost the follow-up. There was no correlation between clinical severity score, Loes score and elevated degree of elevated very long chain fatty acid (VLCFA) levels in CCALD.

Conclusion: Our study reports forty-eight new patients with X-ALD and their long-term outcome. Only 35% of the patients presented with neurological features or Addison disease. The remaining individuals were identified due to positive family history. Close monitoring of asymptomatic males resulted in early HSCT to prevent progressive lethal neurodegenerative disease. Identification of patients with X-ALD is important to improve neurodevelopmental outcome of asymptomatic males.
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http://dx.doi.org/10.1016/j.ejpn.2017.02.006DOI Listing
July 2017

Whole Genome Sequencing Expands Diagnostic Utility and Improves Clinical Management in Pediatric Medicine.

NPJ Genom Med 2016 Jan;1

Division of Clinical and Metabolic Genetics, The Hospital for Sick Children, Toronto, Ontario, Canada.

The standard of care for first-tier clinical investigation of the etiology of congenital malformations and neurodevelopmental disorders is chromosome microarray analysis (CMA) for copy number variations (CNVs), often followed by gene(s)-specific sequencing searching for smaller insertion-deletions (indels) and single nucleotide variant (SNV) mutations. Whole genome sequencing (WGS) has the potential to capture all classes of genetic variation in one experiment; however, the diagnostic yield for mutation detection of WGS compared to CMA, and other tests, needs to be established. In a prospective study we utilized WGS and comprehensive medical annotation to assess 100 patients referred to a paediatric genetics service and compared the diagnostic yield versus standard genetic testing. WGS identified genetic variants meeting clinical diagnostic criteria in 34% of cases, representing a 4-fold increase in diagnostic rate over CMA (8%) (p-value = 1.42e-05) alone and >2-fold increase in CMA plus targeted gene sequencing (13%) (p-value = 0.0009). WGS identified all rare clinically significant CNVs that were detected by CMA. In 26 patients, WGS revealed indel and missense mutations presenting in a dominant (63%) or a recessive (37%) manner. We found four subjects with mutations in at least two genes associated with distinct genetic disorders, including two cases harboring a pathogenic CNV and SNV. When considering medically actionable secondary findings in addition to primary WGS findings, 38% of patients would benefit from genetic counseling. Clinical implementation of WGS as a primary test will provide a higher diagnostic yield than conventional genetic testing and potentially reduce the time required to reach a genetic diagnosis.
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http://dx.doi.org/10.1038/npjgenmed.2015.12DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5447450PMC
January 2016

Diagnostic yield of genetic testing in epileptic encephalopathy in childhood.

Epilepsia 2015 May 25;56(5):707-16. Epub 2015 Mar 25.

Division of Neurology, Department of Paediatrics, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.

Objective: Epilepsy is a common neurologic disorder of childhood. To determine the genetic diagnostic yield in epileptic encephalopathy, we performed a retrospective cohort study in a single epilepsy genetics clinic.

Methods: We included all patients with intractable epilepsy, global developmental delay, and cognitive dysfunction seen between January 2012 and June 2014 in the Epilepsy Genetics Clinic. Electronic patient charts were reviewed for clinical features, neuroimaging, biochemical investigations, and molecular genetic investigations including targeted next-generation sequencing of epileptic encephalopathy genes.

Results: Genetic causes were identified in 28% of the 110 patients: 7% had inherited metabolic disorders including pyridoxine dependent epilepsy caused by ALDH7A1 mutation, Menkes disease, pyridox(am)ine-5-phosphate oxidase deficiency, cobalamin G deficiency, methylenetetrahydrofolate reductase deficiency, glucose transporter 1 deficiency, glycine encephalopathy, and pyruvate dehydrogenase complex deficiency; 21% had other genetic causes including genetic syndromes, pathogenic copy number variants on array comparative genomic hybridization, and epileptic encephalopathy related to mutations in the SCN1A, SCN2A, SCN8A, KCNQ2, STXBP1, PCDH19, and SLC9A6 genes. Forty-five percent of patients obtained a genetic diagnosis by targeted next-generation sequencing epileptic encephalopathy panels. It is notable that 4.5% of patients had a treatable inherited metabolic disease.

Significance: To the best of our knowledge, this is the first study to combine inherited metabolic disorders and other genetic causes of epileptic encephalopathy. Targeted next-generation sequencing panels increased the genetic diagnostic yield from <10% to >25% in patients with epileptic encephalopathy.
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http://dx.doi.org/10.1111/epi.12954DOI Listing
May 2015

The natural history of glycogen storage disease types VI and IX: Long-term outcome from the largest metabolic center in Canada.

Mol Genet Metab 2014 Nov 21;113(3):171-6. Epub 2014 Sep 21.

Division of Clinical and Metabolic Genetics, Department of Pediatrics, University of Toronto, Toronto, ON, Canada; Genetics and Genome Biology Research Program, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada. Electronic address:

Objectives: Glycogen storage disease (GSD) types VI and IX are caused by phosphorylase system deficiencies. To evaluate the natural history and long-term treatment outcome of the patients with GSD-VI and -IX, we performed an observational retrospective case study of 21 patients with confirmed diagnosis of GSD-VI or -IX.

Methods: All patients with GSD-VI or -IX, diagnosed at The Hospital for Sick Children, were included. Electronic and paper charts were reviewed for clinical features, biochemical investigations, molecular genetic testing, diagnostic imaging, long-term outcome and treatment by two independent research team members. All information was entered into an Excel database.

Results: We report on the natural history and treatment outcomes of the 21 patients with GSD-VI and -IX and 16 novel pathogenic mutations in the PHKA2, PHKB, PHKG2 and PYGL genes. We report for the first time likely liver adenoma on liver ultrasound and liver fibrosis on liver biopsy specimens in patients with GSD-VI and mild cardiomyopathy on echocardiography in patients with GSD-VI and -IXb.

Conclusion: We recommend close monitoring in all patients with GSD-VI and -IX for the long-term liver and cardiac complications. There is a need for future studies if uncooked cornstarch and high protein diet would be able to prevent long-term complications of GSD-VI and -IX.
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http://dx.doi.org/10.1016/j.ymgme.2014.09.005DOI Listing
November 2014

Late-onset Zellweger spectrum disorder caused by PEX6 mutations mimicking X-linked adrenoleukodystrophy.

Pediatr Neurol 2014 Aug 28;51(2):262-5. Epub 2014 Mar 28.

Division of Clinical and Metabolic Genetics, The Hospital for Sick Children, Toronto, Ontario, Canada; Genetics & Genome Biology Program, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada. Electronic address:

Background: Zellweger spectrum disorder is an autosomal recessively inherited multisystem disorder caused by one of the 13 different PEX gene defects resulting in defective peroxisomal assembly and multiple peroxisomal enzyme deficiencies. We report a new patient with late-onset Zellweger spectrum disorder mimicking X-linked adrenoleukodystrophy.

Patient Description: This 8.5-year-old boy with normal development until 6.5 years of age presented with bilateral sensorineural hearing loss during a school hearing test. He then developed acute-onset diplopia, clumsiness, and cognitive dysfunction at age 7 years. Magnetic resonance imaging of the brain revealed symmetric leukodystrophy, although without gadolinium enhancement. Elevated plasma very long chain fatty acid levels were suggestive of X-linked adrenoleukodystrophy, but his ABCD1 gene had normal coding sequence and dosage. Additional studies of cultured skin fibroblasts were consistent with Zellweger spectrum disorder. Molecular testing identified disease-causing compound heterozygous mutations in the PEX6 gene supporting the Zellweger spectrum disorder diagnosis in this patient.

Conclusions: We describe a new patient with late-onset Zellweger spectrum disorder caused by PEX6 mutations who presented with an acute neurodegenerative disease course mimicking X-linked adrenoleukodystrophy. This finding provides an additional reason that molecular confirmation is important for the genetic counseling and management of patients with a clinical and biochemical diagnosis of X-linked adrenoleukodystrophy.
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http://dx.doi.org/10.1016/j.pediatrneurol.2014.03.020DOI Listing
August 2014

Danon Disease Due to a Novel LAMP2 Microduplication.

JIMD Rep 2014 13;14:11-6. Epub 2013 Nov 13.

Division of Metabolics and Newborn Screening, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada.

Danon disease is a rare X-linked disorder comprising hypertrophic cardiomyopathy, skeletal myopathy, intellectual disability, and retinopathy; mutations of the lysosome-associated membrane protein gene LAMP2 are responsible. Most affected persons exhibit "private" point mutations; small locus rearrangements have recently been reported in four cases. Here, we describe the clinical, pathologic, and molecular features of a male proband and his affected mother with Danon disease and a small LAMP2 microduplication. The proband presented at age 12 years with exercise intolerance, hypertrophic cardiomyopathy, and increased creatine kinase. Endomyocardial biopsy findings were nonspecific, showing myocyte hypertrophy and reactive mitochondrial changes. Quadriceps muscle biopsy demonstrated the characteristic autophagic vacuoles with sarcolemma-like features. LAMP2 tissue immunostaining was absent; however, LAMP2 sequencing was normal. Deletion/duplication testing by multiplex ligation-dependent probe amplification (MLPA) assay revealed a 1.5kb microduplication containing LAMP2 exons 4 and 5. RT-PCR studies were consistent with the inclusion of these two duplicated exons in the final spliced transcript, resulting in a frameshift. The proband's mother, who had died following cardiac transplantation due to suspected myocarditis at age 35, was reviewed and was shown to be affected upon immunostaining of banked myocardial tissue. This case constitutes the second report of a pathogenic microduplication in Danon disease, and illustrates a number of potential diagnostic pitfalls. Firstly, given the imperfect sensitivity of LAMP2 sequencing, tissue immunostaining and/or MLPA should be considered as a diagnostic adjunct in the workup for this disorder. Secondly, the pathological findings in myocardium may be falsely indicative of relatively common conditions such as myocarditis.
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http://dx.doi.org/10.1007/8904_2013_277DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4213339PMC
October 2014

X-linked adrenoleukodystrophy: ABCD1 de novo mutations and mosaicism.

Mol Genet Metab 2011 Sep-Oct;104(1-2):160-6. Epub 2011 Jun 22.

DNA Diagnostic Laboratory, Johns Hopkins University School of Medicine, CMSC1004, 600 N. Wolfe Street, Baltimore, MD 21287, USA.

X-linked adrenoleukodystrophy (X-ALD) is a progressive peroxisomal disorder affecting adrenal glands, testes and myelin stability that is caused by mutations in the ABCD1 (NM_000033) gene. Males with X-ALD may be diagnosed by the demonstration of elevated very long chain fatty acid (VLCFA) levels in plasma. In contrast, only 80% of female carriers have elevated plasma VLCFA; therefore targeted mutation analysis is the most effective means for carrier detection. Amongst 489 X-ALD families tested at Kennedy Krieger Institute, we identified 20 cases in which the ABCD1 mutation was de novo in the index case, indicating that the mutation arose in the maternal germ line and supporting a new mutation rate of at least 4.1% for this group. In addition, we identified 10 cases in which a de novo mutation arose in the mother or the grandmother of the index case. In two of these cases studies indicated that the mothers were low level gonosomal mosaics. In a third case biochemical, molecular and pedigree analysis indicated the mother was a gonadal mosaic. To the best of our knowledge mosaicism has not been previously reported in X-ALD. In addition, we identified one pedigree in which the maternal grandfather was mosaic for the familial ABCD1 mutation. Less than 1% of our patient population had evidence of gonadal or gonosomal mosaicism, suggesting it is a rare occurrence for this gene and its associated disorders. However, the residual maternal risk for having additional ovum carrying the mutant allele identified in an index case that appears to have a de novo mutation is at least 13%.
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http://dx.doi.org/10.1016/j.ymgme.2011.05.016DOI Listing
January 2012

A sociolinguistic exploration of genetic counseling discourse involving a child with a new genetic diagnosis.

Patient Educ Couns 2010 Jan 21;78(1):40-5. Epub 2009 Aug 21.

Division of Clinical and Metabolic Genetics, The Hospital for Sick Children, Toronto, ON, Canada, M5G 1X8.

Objectives: To examine the process of genetic counseling with the aim of observing how participants negotiate a common understanding in light of the inherent power asymmetry of a genetics health care encounter.

Methods: Data from ten sessions between genetic counselors and parents of children with a genetic diagnosis were taped. Transcripts were examined using a qualitative discourse analysis approach focusing on communication features such as question design, topic initiation and control, and lexical or discourse features which could give insights into rapport building strategies.

Results: Counselors tightly controlled the medical history phase in all sessions and verbally dominated the scientific information phase. More symmetric communication occurred when: (i) counselors showed flexibility with their agenda and gave parents the opportunity to share their health experience; (ii) counselors showed signs of involvement through the use of 'rapport building' strategies; (iii) counselors used a syllogistic approach and information was delivered at a slower pace.

Conclusion: Observations from this study suggest that, when counselors focus on building rapport with parents, the human voice of the parent emerges. Examples of rapport building strategies by the counselors included adapting to the parents' variations in knowledge, recognizing the needs of the parents, verifying their understanding, and choosing a more interactive approach to the delivery of information.

Practice Implications: Our findings suggest that for effective communication to occur, parents need to be provided with opportunities to be active participants in the genetic counseling encounter.
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http://dx.doi.org/10.1016/j.pec.2009.06.007DOI Listing
January 2010

Assessing the informational needs of adolescents with a genetic condition: what do they want to know?

J Genet Couns 2007 Apr;16(2):201-10

Division of Clinical and Metabolic Genetics, The Hospital for Sick Children, Toronto, ON, Canada.

Adolescence is a period of challenges that can be more stressful for someone with a genetic condition. The purpose of this descriptive pilot study was to assess the informational needs of adolescents with a genetic condition. To our knowledge, this is the first study that has attempted to identify these needs. A convenience sample of adolescents between 12-19 years of age with either phenylketonuria or congenital adrenal hyperplasia and who had not previously received genetic counseling was recruited. Recruitment ended once the themes were saturated (n=17). A twenty item open/close-ended questionnaire was used to assess participants' knowledge of their genetic condition, what they wanted to know about their condition and in what manner. Almost all of the adolescents knew the name and genetic basis of their condition while most were aware of the risk of recurrence in a future pregnancy. Parents and doctors respectively, were identified as the primary and secondary sources of genetic information. Despite their evolving independence, almost all of the participants favoured receiving medical information with their parents present. The majority of participants felt that patients should begin receiving genetic information before the age of 12 years. Thematic analysis revealed that adolescents wanted to understand the science behind their condition, how their condition affects them, and how to manage it. The results highlight (i) the importance that adolescents place on parental involvement in their medical care (ii) that adolescents would like information about the genetics of their condition at a much younger age than when they usually receive genetic counseling and (iii) the benefits that can be gained by this patient population from receiving genetic counseling.
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http://dx.doi.org/10.1007/s10897-006-9060-5DOI Listing
April 2007

Canavan disease: carrier-frequency determination in the Ashkenazi Jewish population and development of a novel molecular diagnostic assay.

Am J Med Genet A 2004 Jan;124A(2):142-7

Division of Clinical and Metabolic Genetics, Department of Pediatrics, The Hospital For Sick Children, The University of Toronto, Toronto, Canada.

Canavan disease (CD) is an autosomal recessive progressive neurodegenerative disorder prevalent in the Ashkenazi Jewish (AJ) population. The carrier rate for the most common mutations that cause CD in the AJ population is often quoted as 1:37-1:40. This is not supported by our finding of only two diagnosed cases of CD in the last 20 years in the Toronto AJ population of 160,000 and an estimated birth rate of 1,500-2,000 per year. Therefore, we embarked on a prevalence cross-sectional screening study to determine the carrier rate of CD in this population. In order to perform low-cost, high-throughput population testing for CD using molecular techniques, we first developed a novel molecular assay using multiplex fluorescent allele specific polymerase chain reaction (PCR) to test for the three most common mutations causing CD in the AJ population (A854C, C693A, C914A) and a neutral polymorphism at the site of the C693A mutation. During testing it was noted that individuals who were carriers of the A854C mutation also had a T polymorphism at the site of the C693A mutation (Y231X). We confirmed that in all A854C carriers the 854C mutation was in disequilibrium with the 693T polymorphism, indicating a founder chromosome for the A854C mutation in the AJ population. Twenty-five carriers were found from 1,423 samples yielding a carrier rate of 1:57, differing from the widely quoted frequency of 1:40 and supporting our observed frequency of disease.
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http://dx.doi.org/10.1002/ajmg.a.20334DOI Listing
January 2004
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