Congenital hypothyroidism due to thyroid disgenesis: whole exome investigation of molecular genetics and cromossomal alterations

Abstract

Congenital hypothyroidism (CH) is the most frequent pediatric endocrine syndrome (1: 1.500 to 1: 4.000 newborns). Embryological defects of the thyroid gland or thyroid dysgenesis (TD) account for 75-85% of the cases of CH. TD includes thyroid agenesis (absence of thyroid tissue, 15%), ectopia (thyroid tissue located outside of the normal position, 65%) and hypoplasia (reduced-size gland in normal position, 10%). Mutations have been identified in 5% of TD patients in PAX-8 and TSH receptor genes, and in FOXE1, NKX2.1, NKX2.5 and TBX1 genes (associated with other malformations). Up to now, it has not been established the inheritance pattern of TD, if there is genetic heterogeneity or if new genes are involved. Thus, it is a consensus that TD is still a puzzle that needs to be solved. Therefore, the aim of this this study is to expand the investigations of the molecular basis of TD through the identification of genetic or chromosomal abnormalities with clinical relevance by sequencing the whole-exome (WES) and regulatory regions (UTRs and microRNAs connection) of patients with TD. This study will include 45 TD patients, not harboring mutations in PAX8 or TSHR genes, divided in three groups: ectopia, atireosis and hypoplasia. Clinical and laboratorial data of the patients and samples of peripheral blood for DNA extraction will be collected. Next-generation sequencing will be performed with the capture of the expanded exome and 200X coverage in Illumina® NextSeq" 500 platform, that spans ~62Mb/sample. The overall sequences will be compared with the human reference sequence (GRCh37/Hg19) and other databases to select gene variants (SNPs), small insertions and deletions, copy number variations (CNVs) and other chromosomal alteration with clinical significance. The screening of 150 normal control DNA samples will also validate the results. This project is original, will described new genes and molecular pathways involved in the pathogenesis of DTs, will evaluate the genotype/phenotype correlation and the presence of allelic or locus heterogeneity. These data may also help the monitoring of patients and will contribute to the understanding of the genetic control of "normal thyroid development". (AU)