ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2013) 33 OC2.9 | DOI: 10.1530/endoabs.33.OC2.9

A comprehensive next generation sequencing-based strategy for genetic diagnosis in congenital hypothyroidism

Nadia Schoenmakers1, Hakan Cangul2, Adeline K Nicholas1, Erik Schoenmakers1, Greta Lyons1, Mehul Dattani3, Catherine Peters4, Shirley Langham4, Abdelhadi M Habeb5, Asma Deeb6, Vijith Puthi7, Soo-Mi Park8, Marina Muzza9, Luca Persani10, Laura Fugazzola9, Eamonn Maher8 & V Krishna Chatterjee1

1Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, University of Cambridge, Cambridge, UK; 2Department of Medical Genetics, Bahcesehir University School of Medicine, Istanbul, Turkey; 3Developmental Endocrinology Research Group, Clinical and Molecular Genetics Unit, Department of Endocrinology, UCL Institute of Child Health, Great Ormond Street Hospital, London, UK; 4Department of Endocrinology, Great Ormond Street Hospital, London, UK; 5Paediatric Endocrine Unit, Maternity and Childrens Hospital, Madinah, Saudi Arabia; 6Department of Paediatric Endocrinology, Mafraq Hospital, AbuDhabi, United Arab Emirates; 7Department of Paediatrics, Peterborough City Hospital, Peterborough, UK; 8Department of Clinical Genetics, Addenbrooke’s Hospital, Cambridge, UK; 9Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy; 10Department of Clinical Sciences and Community Health, Istituto Auxologico Italiano, University of Milan, Milan, Italy.

Introduction: Less than 20% of congenital hypothyroidism (CH) has a known genetic aetiology; thyroid transcription factor mutations (PAX8, Nkx2.1, Nkx2.5, FOXE1) or biallelic TSHR mutations cause <5% of thyroid dysgenesis (TD), whereas mutations in genes mediating thyroid hormone biosynthesis (TPO, TG, DUOX2, DUOXA2, IYD, SLC5A5, SLC26A4) account for most dyshormonogenesis cases. Increased CH frequency in consanguineous populations, relatives of TD cases, and in conjunction with extrathyroidal anomalies suggests involvement of hitherto unidentified genes.

Although genetic diagnosis is not routinely undertaken, establishing the molecular basis of CH may inform treatment, anticipate extrathyroidal features and confirm recurrence risk to facilitate genetic counselling. Prediction of genetic basis from clinical phenotype is unreliable, precluding implementation of selective candidate gene analysis; accordingly, a comprehensive genetic screening strategy has been developed.

Method: Compared to conventional sequencing, next generation sequencing (NGS) technologies increase sequencing capacity and speed, with molecular ‘barcodes’ enabling multiplex analysis of samples, to improve throughput and efficiency. 11 known and 20 putative CH-associated genes were screened using NGS in 49 families. This genetic diagnostic strategy aimed to identify mutations in known and predicted CH-associated genes and to delineate a ‘mutation-negative’ cohort in whom novel genetic causes can be sought.

Results: Ten families harboured mutations in known causative genes, of which five were known (DUOX2: Q686X, R354W, TPO: R665Q, R491H, TG R277X) and six were novel (DUOX2: Q570L, TG: S509X, R140X W1031L, C707Y, T1397RfsX30, c.638+5 G>A); two families harboured compound TG mutations.

Conclusion: NGS enables efficient screening of multiple genes simultaneously, facilitating genetic diagnosis in CH. Such comprehensive screening will identify mutations in known genes associated with atypical clinical phenotypes, and in putative CH-associated genes identified from animal models. Identification of ‘mutation-negative’ cases defines a population in whom whole exome sequencing may identify novel genetic aetiologies for CH, elucidating novel pathways in thyroid development and physiology.