Autoimmune thyroiditis associated with mild "subclinical" hypothyroidism in adults with Down syndrome: a comparison of patients with and without manifestations of Alzheimer disease

Serum tests of thyroid function were compared in Down syndrome (DS) patients with and without manifestations of Alzheimer disease (AD). Relative to control individuals, DS patients had, overall, lower mean total T4 (P = 0.070) and T3f (P = 0.015), higher T3U (P = 0.013) and TSH (P = 0.020), no difference in free T4, and higher thyroid antithyroglobulin (ATA) (P = 0.033) and antimicrosomal autoantibody (AMA) titres (P = 0.0097). Similar trends were apparent in DS males and females, and in DS patients off all drugs. In an analysis of case/control pairs with corrections for age and sex, DS patients with AD manifestations (n = 9) had significantly lower T3 (P = 0.029) and higher AMA (P = 0.043) than paired control individuals, whereas DS patients without AD manifestations (n = 20) had significantly lower T3 (P = 0.013) but higher ATA (P = 0.0065). T3 was significantly lower in the DS patients with AD manifestations than in the unaffected (P = 0.0013). These data suggest that autoimmune thyroiditis associated with a mild "subclinical" form of hypothyroidism is common in adult DS patients and more pronounced in patients with AD manifestations than in those without. This "subclinical" hypothyroidism may contribute to cognitive deficits in ageing DS patients.

Problems in screening for congenital hypothyroidism using thyroxine assays from small dried blood discs

The feasibility of screening for neonatal hypothyroidism by initial thyroxine (T4) measurements from small (3.2 mm diam.) discs of dried heel or cord blood was assessed using double-antibody radioimmunoassay and solid-phase radioassay kits. Adult heparinized venous blood or finger-prick capillary blood served as references. Reproducibility of results was satisfactory in adult but not infant samples, probably because of problems in collecting and handling the latter. In comparative studies, most of the 16 infants with congenital primary hypothyroidism had within-run T4 values above the 2.5 percentile; some were as high as the 7th and the 5th percentile for heel and cord blood, respectively. Simultaneously determined heel and cord dried-blood thyrotropin (TSH) values were clearly increased to greater than 40 microU/ml in 15 of these infants. Thus, when small discs are used for initial blood T4 screening to detect primary hypothyroidism, a higher cut-off points is recommended to safeguard against the observed technical problems.

A rapid double antibody non-equilibrium serum thyrotropin radioimmunnoassay suitable for primary neonatal hypothyroidism screening

An improved double antibody radioimmunoassay for measuring human thyrotropin (h-TSH) in serum, suitable for neonatal primary hypothyroidism screening is described. The assay employs a non-equilibrium double antibody technique performed at an initial 37 degrees C followed by incubation at room temperature. Studies on the effects of various reaction parameters including time, temperature, antigen and antibody concentrations and the effect of various carrier proteins on the performance of standard curves were also performed. Using a 100-microliter serum sample for analysis, the assay sensitivity is routinely between 3 and 6 microU/mol of h-TSH (MRC 68/38) with interassay and intra-assay coefficient of variation values ranging from 6 to 14% over a wide range of control values. The incubation and phase separation is completed after 26 h with data available following automated counting and computation. Such a rapid assay facilitates a neonatal screening program for the early detection and treatment of primary neonatal hypothyroidism using either cord blood serum or early follow-up serum sampling in infants suspected on initial screening tests of an abnormality.