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The rate of fall of serum thyroid stimulating hormone (TSH) concentrations in 32 hypothyroid infants (11 boys, 21 girls) was studied after starting treatment with thyroxine to determine whether it was influenced by initial TSH concentration or the cause of the hypothyroidism. Of 27 patients who had isotope scans before treatment was started, 11 (40%) were athyrotic, 10 (38%) had an ectopic gland, and six (22%) probably had dyshormonogenesis. Treatment was started with thyroxine at 100 micrograms/m2/24 hours at a mean age of 26 days (range 14-45). Serum TSH concentrations remained increased in 26 (81%) at 3 months, 20 (62.5%) at 6 months, and nine (28%) at 1 year and beyond. The mean age for serum TSH to reach the normal range was 0.79 years (range 0.15-2.1 years). Diagnosis (in 27 patients) and initial results (in 32) made no difference to the rate of fall.

Two siblings had sublingual thyroid glands and hypothyroidism. A third sibling had a left lobe agenesis of the thyroid, but normal function of the gland. This is the second such family to be described.

Screening in the North West health region of England showed a significantly higher incidence of congenital hypothyroidism in Asian families--1/918 compared with 1/3391 in non-Asians. This could only in part be explained by consanguinity. No differences were found in birth order, season of birth, gestational age, or birth weight between normal infants and those with congenital hypothyroidism. There was a significantly higher incidence of additional congenital abnormalities (9%) and a significantly increased mortality (5%) in infants with congenital hypothyroidism compared with unaffected infants.

Serum thyrotrophin (TSH) was estimated by double-antibody radioimmunoassay in 200 children aged 2 months to 16 years with normal thyroid function. There was no apparent variation in TSH with age or sex and only 4 children had TSH levels greater than 5 muU/ml. High TSH values were obtained in 9 children with primary hypothyroidism, in 3 children with thyroiditis, and in one girl with a lingual thyroid. Moderately raised TSH was found in 3 girls with thyroiditis, 2 brothers with goitres due to enzyme defect, and a girl with an ectopic thyroid. In one girl with a defect of iodine organification and in 3 boys with thyroxine binding globulin deficiency the TSH levels were normal despite very low serum thyroxine values. Serum TSH was also estimated in 20 children during treatment for primary hypothyroidism. 3 of these children showed slightly raised TSH levels despite apparently adequate replacement therapy with L-thyroxine. One girl showed a very high TSH level 3 weeks after treatment had been temporarily withdrawn.

Seven of the 34 infants identified through the Welsh Hypothyroid Screening Programme have additional congenital abnormalities. Two infants have a previously undescribed syndrome, two have chromosomal abnormalities, two have congenital heart disease, and one has a myelomeningocoele. Congenital hypothyroidism often seems to be associated with other congenital abnormalities.