ESPE Abstracts

Congenital hypothyroidism (CH) is a partial or complete loss of function of the thyroid gland resulting in absent or decreased synthesis and secretion of thyroid hormones affecting infants since birth. Mutations of the hTPO gene are associated with autosomal recessive forms of CH. Based on our TSH screening results, the number of children with eutopic primary CH is increasing. Molecular biology techniques can identify the CH genetic cause after selection based on family history, thyroid morphology and baseline hormonal data. The identification of Tg or TPO mutation suggests a risk of thyroid cancer within the goiter in adulthood. It is unclear whether the thyroid cancer is gene-specific event or related to goiter development. TPO is mediating two central steps of thyroid hormone synthesis: 1) Organification of iodide to iodinated tyrosyl residues and 2) Coupling of MIT and DIT to T3 and T4. Aim: To set up a multistep mutational screening strategy in CH patients with eutopic thyroids, starting by the analysis of the hTPO gene. Material and Methods: Using the candidate gene approach (permanent CH, eutopic thyroid, elevated Tg) selection of patients suitable for hTPO molecular analysis was performed. Thirty nine patients from 32 families were included. Molecular analysis on genomic DNA was done by Sanger sequencing and MLPA. Results: Seven different mutations were found by Sanger sequencing-c.31_50dup, p.(Glu17AspfsTer77),in exon 2; c.819+4A>C (2.6%), and c.621_622delGG,: p.(Glu207AspfsTer11) (1.3%) – both in exon 7, the second one is novel; c.1430_1450del, p.(Ala477Asn483del), in exon 9 (1.3%), and one whole gene deletion detected by MLPA analysis. In 8 of the 39 patients (20.5%) the phenotype could be explained by the genotype: 3 of all patients showed homozygous mutations - rs76366277:c.2422delT p.(Cys808AlafsTer24), exon 14 (6.4%); rs17855780, c.208C>G, p.(Pro70Ala), exon 4 (5.1%), and a novel one c.1268G>A, p.Gly393ARG in 8 exon (2.6%), 3 were compound heterozygous carriers. 2 of the patients (2.6%) were carriers of heterozygous deletions of all exons included in the MLPA kit. Conclusions: There is considerable heterogeneity among the hTPO gene mutations in the screened population and novel mutations were found. Some patients with large eutopic glands, high Tg and severe CH were negative in the present mutational screen, therefore NGS is the next step of analysis that could establish the genetic causes of CH in Bulgarian patients.