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Pathogenic mitochondrial tRNA (mt-tRNA) gene mutations represent a prominent cause of primary mitochondrial DNA (mtDNA)-related disease despite accounting for only 5%-10% of the mitochondrial genome.(1,2) Although some common mt-tRNA mutations, such as the m.3243A>G mutation, exist, the majority are rare and have been reported in only a small number of cases.(3) The MT-TP gene, encoding mt-tRNA(Pro), is one of the less polymorphic mt-tRNA genes, and only 5 MT-TP mutations have been reported as a cause of mitochondrial muscle disease to date (table e-1 at Neurology.org/ng, P6-10). We report 5 patients with myopathic phenotypes, each harboring different pathogenic mutations in the MT-TP gene, highlighting the importance of MT-TP mutations as a cause of mitochondrial muscle disease and the requirement to study clinically relevant tissue.

Study Question: What is the likelihood of identifying genetic or endocrine abnormalities in a group of boys with 46, XY who present to a specialist clinic with a suspected disorder of sex development (DSD)?Summary Answer: An endocrine abnormality of the gonadal axis may be present in a quarter of cases and copy number variants (CNVs) or single gene variants may be present in about half of the cases.What Is Known Already: Evaluation of 46, XY DSD requires a combination of endocrine and genetic tests but the prevalence of these abnormalities in a sufficiently large group of boys presenting to one specialist multidisciplinary service is unclear.Study, Design, Size, Duration: This study was a retrospective review of investigations performed on 122 boys.Participants/materials, Setting, Methods: All boys who attended the Glasgow DSD clinic, between 2010 and 2015 were included in the study. The median external masculinization score (EMS) of this group was 9 (range 1-11). Details of phenotype, endocrine and genetic investigations were obtained from case records.Main Results and the Role Of Chance: An endocrine abnormality of gonadal function was present in 28 (23%) with a median EMS of 8.3 (1-10.5) whilst the median EMS of boys with normal endocrine investigations was 9 (1.5-11) (P = 0.03). Endocrine abnormalities included a disorder of gonadal development in 19 (16%), LH deficiency in 5 (4%) and a disorder of androgen synthesis in 4 (3%) boys. Of 43 cases who had array-comparative genomic hybridization (array-CGH), CNVs were reported in 13 (30%) with a median EMS of 8.5 (1.5-11). Candidate gene analysis using a limited seven-gene panel in 64 boys identified variants in 9 (14%) with a median EMS of 8 (1-9). Of the 21 boys with a genetic abnormality, 11 (52%) had normal endocrine investigations.Limitations, Reasons For Caution: A selection bias for performing array-CGH in cases with multiple congenital malformations may have led to a high yield of CNVs. It is also possible that the yield of single gene variants may have been higher than reported if the investigators had used a more extended gene panel.Wider Implications Of the Findings: The lack of a clear association between the extent of under-masculinization and presence of endocrine and genetic abnormalities suggests a role for parallel endocrine and genetic investigations in cases of suspected XY DSD.Study Funding/competing Interest(s): RN was supported by the James Paterson Bursary and the Glasgow Children's Hospital Charity Summer Scholarship. SFA, RM and EST are supported by a Scottish Executive Health Department grant 74250/1 for the Scottish Genomes Partnership. EST is also supported by MRC/EPSRC Molecular Pathology Node and Wellcome Trust ISSF funding. There are no conflicts of interest.Trial Registration Number: None. [ABSTRACT FROM AUTHOR]