Endocrine Abstracts

Congenital hypothyroidism (CH) occurs in approximately 1 in 3000 individuals. Rapid detection by neonatal screening and T4 administration is essential to prevent severe mental retardation and impaired growth. About one third of CH is due to mutations in known genes including the thyrotropin receptor (TSHR).

Two Welsh male siblings with CH were detected, both had normally sized and located thyroid glands, no iodide uptake and were negative for thyroid blocking antibodies. We investigated the possibility of TSHR mutation.

DNA from both siblings and their parents was obtained. The TSHR was amplified using 9 pairs of intronic primers for exons 1-9 and 2 pairs of intronic with overlapping exonic primers for exon 10. PCR products were sequenced on an ABI automated sequencer.

Both siblings were homozygous for a previously described inactivating mutation W546X, resulting in a premature stop codon in the 4th membrane spanning region of the TSHR encoding a truncated protein. Both parents were heterozygous (wild type/W546X), euthyroid and unrelated. We are aware of at least two other pairs of siblings (one Welsh) who are compound heterozygotes of which one allele is the W546X mutation, implying that it is a common allele. We have estimated the frequency of the W546X allele to be ~1%, in 2 different pools of DNA from 184 Welsh blood donors, using mini sequencing, although this is within the error limit of the method. We will apply the technique to genotype the individuals in the pooled DNA which will enable us to determine its frequency in the population and whether it contributes to the regional variation in CH in Wales, 1: 1800 in the north and west but 1: 3500 in the south and east.