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TO THE EDITOR. — Tajiri and colleagues1 in their article on antithyroid druginduced agranulocytosis note that "... routine monitoring of the white blood cell count could be the most effective way of predicting and detecting..." the condition. Although the statement is true for the majority of the patients with this condition, "monitoring of the white blood cell count" is totally useless for the detection of antithyroid drug-induced agranulocytosis in some cases because agranulocytosis can occur in the presence of a normal total white blood cell count; such aspect of the problem is unduly neglected in the article.1 The authors only mentioned that the white blood cell count is normal in some cases until immediately before the development of agranulocytosis. We report herein our experience and result of the survey of English-language literature concerning this issue. REPORT OF A CASE. — A 57-year-old woman developed fever on March 14, 1990,

Steroid 21-hydroxylase (21-OH) is a key haem containing steroidogenic enzyme and a major adrenal specific autoantigen. Cys 428 in 21-OH is thought to have an important role in haem binding and we now describe the effects of mutations at Cys 428 (to Ser, Arg and Phe) on 21-OH autoantibody binding. Expression of wild type and mutated 21-OH was carried out using an in vitro transcription/translation (TnT) system and reactivity of 21-OH autoantibodies with mutated 21-OH analysed by western blotting (in the case of unlabelled proteins) or immunoprecipitation assay (IPA) (in the case of 35S-labelled proteins). All 3 substitutions at Cys 428 had similar effects on 21-OH autoantibody binding and each one caused a reduction in autoantibody binding to about 50 of wild type in the case of IPA and to about 70 of wild type in the case of western blotting analysis. In addition to mutations at Cys 428, we studied 2 naturally occurring mutations at Pro 30 to Leu and He 172 to Asn which are associated with diminished 21-OH enzyme activity. The Pro 30 mutation had no effect, but the He 172 mutation caused a reduction in 21-OH autoantibody binding in the IPA to about 80 of wild type.Overall, our studies emphasise the close relationship between the 21-OH aminoacid sequences important for 21-OH enzyme activity and 21-OH autoantibody binding.

The role of the renin–aldosterone system and the ability of renal sodium reabsorption to facilitate pressure natriuresis were analyzed by using a sufficient number of Japanese patients with essential hypertension.

We describe a new method for measuring autoantibodies (Ab) to the 65 kDa isoform of glutamic acid decarboxylase (GAD65). In particular, GAD65without the hydrophobic N-terminal region has been produced in yeast, purified, labelled with 125I and reacted with GAD65Ab. Antibody bound 125I-GAD65is then precipitated by the addition of solid phase protein A. With the assay, GAD65Ab were detected in 59 of 71 (83%) islet cell antibody (ICA) positive IDDM patients and in 8 of 23 (35%) ICA negative IDDM patients (overall 67 of 94 (71%) of IDDM patients). Low concentrations of GAD65Ab were also detected in 298(2%) healthy blood donors and 127(4%) Graves' disease patients had a high level of antibody. GAD65Ab were not detected in any of 10 Hashimoto's thyroiditis, 20 Addison's disease or 19 myasthenia gravis sera. There was good agreement between the 125I assay and the current reference method based on 35S-labelled full-length GAD65(produced by in vitro transcription/translation reaction) and solid phase protein A (r= 0.91, n= 108). Overall, our 125I assay showed sensitivity, precision and disease group specificity at least as good as any assay so far described. These features, combined with a simple assay protocol and the convenience of 125I counting and handling indicate that the method is suitable for routine GAD65Ab measurements.