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Expanding the clinical phenotype of IARS2-related mitochondrial disease.

ABSTRACT: BACKGROUND:IARS2 encodes a mitochondrial isoleucyl-tRNA synthetase, a highly conserved nuclear-encoded enzyme required for the charging of tRNAs with their cognate amino acid for translation. Recently, pathogenic IARS2 variants have been identified in a number of patients presenting broad clinical phenotypes with autosomal recessive inheritance. These phenotypes range from Leigh and West syndrome to a new syndrome abbreviated CAGSSS that is characterised by cataracts, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss, and skeletal dysplasia, as well as cataract with no additional anomalies. METHODS:Genomic DNA from Iranian probands from two families with consanguineous parental background and overlapping CAGSSS features were subjected to exome sequencing and bioinformatics analysis. RESULTS:Exome sequencing and data analysis revealed a novel homozygous missense variant (c.2625C?>?T, p.Pro909Ser, NM_018060.3) within a 14.3 Mb run of homozygosity in proband 1 and a novel homozygous missense variant (c.2282A?>?G, p.His761Arg) residing in an ~?8 Mb region of homozygosity in a proband of the second family. Patient-derived fibroblasts from proband 1 showed normal respiratory chain enzyme activity, as well as unchanged oxidative phosphorylation protein subunits and IARS2 levels. Homology modelling of the known and novel amino acid residue substitutions in IARS2 provided insight into the possible consequence of these variants on function and structure of the protein. CONCLUSIONS:This study further expands the phenotypic spectrum of IARS2 pathogenic variants to include two patients (patients 2 and 3) with cataract and skeletal dysplasia and no other features of CAGSSS to the possible presentation of the defects in IARS2. Additionally, this study suggests that adult patients with CAGSSS may manifest central adrenal insufficiency and type II esophageal achalasia and proposes that a variable sensorineural hearing loss onset, proportionate short stature, polyneuropathy, and mild dysmorphic features are possible, as seen in patient 1. Our findings support that even though biallelic IARS2 pathogenic variants can result in a distinctive, clinically recognisable phenotype in humans, it can also show a wide range of clinical presentation from severe pediatric neurological disorders of Leigh and West syndrome to both non-syndromic cataract and cataract accompanied by skeletal dysplasia.

SUBMITTER: Vona B

PROVIDER: S-EPMC6233262 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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Expanding the clinical phenotype of IARS2-related mitochondrial disease.

Vona Barbara B Maroofian Reza R Bellacchio Emanuele E Najafi Maryam M Thompson Kyle K Alahmad Ahmad A He Langping L Ahangari Najmeh N Rad Abolfazl A Shahrokhzadeh Sima S Bahena Paulina P Mittag Falk F Traub Frank F Movaffagh Jebrail J Amiri Nafise N Doosti Mohammad M Boostani Reza R Shirzadeh Ebrahim E Haaf Thomas T Diodato Daria D Schmidts Miriam M Taylor Robert W RW Karimiani Ehsan Ghayoor EG

BMC medical genetics 20181112 1

<h4>Background</h4>IARS2 encodes a mitochondrial isoleucyl-tRNA synthetase, a highly conserved nuclear-encoded enzyme required for the charging of tRNAs with their cognate amino acid for translation. Recently, pathogenic IARS2 variants have been identified in a number of patients presenting broad clinical phenotypes with autosomal recessive inheritance. These phenotypes range from Leigh and West syndrome to a new syndrome abbreviated CAGSSS that is characterised by cataracts, growth hormone defi ...[more]

PMID: 30419932

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Project description:BackgroundIARS2 (EC6.1.5) is a mitochondrial isoleucine-tRNA synthetase. Despite the fact that only fewer than 30 patients have been reported in the literature, mitochondrial disorders caused by pathogenic variants in the IARS2 gene (OMIM: 616007) have a very broad and variable clinical phenotype spectrum. We present a child who has sideroblastic anemia and hypoparathyroidism as a result of a previously unreported mutation in the IARS2 gene.Case presentationA 14-year-old girl who had been anemic for 12 years was diagnosed with pure red cell aplasia (hemoglobin 42 g/L, reference range 110-160) at the age of 2. Her anemia was resistant to high-dose intravenous gamma globulin and cyclosporine therapy and required monthly blood transfusions to maintain normal hemoglobin levels. She developed cataracts at the age of 6 and was cured by phacoemulsification. At the age of 8, she visited the endocrine department, because of mental and physical retardation accompanied by repeated convulsions, and the antiepileptic treatment was ineffective. She was diagnosed with hypoparathyroidism. To control the convulsions, she was given calcitriol orally as well as large doses of calcium supplements. Due to severe growth and development delays, delayed sexual development, and hypokinesia at the age of 13.5Y, the parents agreed to a whole-exon gene sequencing test. IARS2 gene compound heterozygous variants c.2450G > A (p.Arg817His) and c.2511del (p.Leu838Phefs*69) were discovered. The girl was then diagnosed with IARS2-related disease and given a cocktail therapy of coenzyme Q10, vitamin B2, L-Carnitine and vitamin E. Although the child's clinical symptoms improved, she still experienced intermittent claudication and hip joint pain. The vitamin B6 was discontinued after three months due to its ineffectiveness in treating anemia. Because the child's ferritin levels remained elevated, she was also prescribed long-term oral deferiprone therapy.ConclusionOur findings broaden the clinical and genetic spectrum of IARS2-associated disease, and case summaries help raise clinical awareness of IARS2-associated disease and reduce under- and misdiagnosis.

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Expanding the clinical phenotype of IARS2-related mitochondrial disease.

Publications

Expanding the clinical phenotype of IARS2-related mitochondrial disease.

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