Abstract
H2O2 generation is a crucial step in thyroid hormonogenesis. The protein responsible for this activity is DUOX2. After the initial description of 4 nonsense mono- and biallelic DUOX2 mutations in patients with transient or permanent congenital hypothyroidism (CH), a few missense mutations have been reported. Molecular clues if this type of CH is transient or permanent, including the severity of the mutations and the number of alleles affected, remain to be established.
Methods: We screened the DUOX2 gene in a large international cohort of 97 patients with permanent or transient CH (including hyperthyrotropinemia) of proven dyshormonogenetic origin.
Results: We identified 18 novel heterozygous mutations in a total of 34 patients. Two are nonsense mutations generating prematurely truncated proteins (K530X, Q1301X), 14 change one amino acid (P311L, R354W, R422S, Q570E, E641K, H678R, R701Q, R726W, A728T, M883I, P982A, R1110Q, A1127G and L1343F) and 2 (IVS13-1C, IVS27+2A) alter a splice-site. Topographically. 6 mutations are located in the peroxidase-like domain, 6 in the 1st intracellular, EF-hand-containing loop, and (for the first time described) 6 in the oxidase (NOX) domain of DUOX2. SIFT, Polyphen and Blosum62 computer programs predict damaging or possibly damaging effects of most of these mutations (n=12) on DUOX2 function. We are developing a highly sensitive H2O2 generation assay to determine the severity of mutations in vitro, and properly evaluate genotype-phenotype correlations. Interestingly, mutations H678R, R701Q and P982A appear genetically linked and, in 50% of cases, are associated with another mutated DUOX2.
Conclusions: We found DUOX2 mutations in approximately 30% of CH patients with a gland in situ, whenever behaving as transient or permanent. Most mutations are predicted to be pathogenic. In vitro determination of functional impact of individual (and linked) DUOX2 changes will allow adequate genotype-phenotype correlations.