SummaryOBJECTIVEFollowing the chance observation of congenital adrenal hyperplasia in a patient with Turner's syndrome we decided to evaluate the incidence of 21‐hydroxylase deficiency (21‐OHD) in patients with Turner's syndrome and in their relatives.SUBJECTSFifty‐two patients with Turner's syndrome (mean age ± SD 14.7 ± 5.6 years) and 26 relatives were studied.MEASUREMENTS17‐Hydroxy progesterone (17‐OHP) serum levels before and after i.m. administration of 0.25 mg of ACTH(1‐24) were evaluated in patients with Turner's syndrome and relatives. In Turner patients basal testosterone and dehydroepiandrosterone concentrations were determined. The results of ACTH tests were analysed according to HLA class I and II alleles of subjects.RESULTSThe baseline 17‐OHP was in the range of the classical form of 21‐OHD in one Turner patient, who had severe clitoral enlargement since birth. In 11 patients the stimulated 17‐OHP serum level was higher than in normal controls and similar to that found in 21‐OHD heterozygous subjects. Clitoral enlargement was significantly more frequent in patients with high stimulated 17‐OHP levels (P<0.001). The frequency of heterozygous‐type responses was higher in Turner subjects (1:4.6) than in the Italian population (1:47 for the classic form and 1:9.5 for the non‐classic form of the disease). In our patients the frequencies of HLA antigens and haplotypes, usually associated with 21‐OHD, were different compared to the controls. HLA‐B8, which is negatively associated to 21‐OHD, was less frequent in Turner patients than in controls and absent in those with an elevated 17‐OHP level. HLA‐B14, B22 and B35 were more frequent, though not significantly so, in Turner patients than in controls and even more so in the group with an elevated 17‐OHP level. The same investigations performed in 26 relatives of the Turner patients showed a high frequency of carriers of 21‐OHD and three subjects with the cryptic form of the disease.CONCLUSIONSAlthough in the literature there are only two reports of the association of Turner's syndrome and 21‐OHD, on the basis of our experience this association was more frequent, in the Italian population. Since some of the typical signs of 21‐OHD (short final stature, varying degrees of virilization, menstrual irregularities, amenorrhoea, infertility) in patients with Turner's syndrome could also be attributed to the chromosomal abnormality, it is therefore more difficult to diagnose 21‐OHD in Turner subjects. Adrenal function should be assessed, at least in the presence of clitoral enlargement, in patients with Turner's syndrome, particularly if their karyotype does not contain a Y chromosome. The hypothesis of the presence of cryptic Y chromosome material in these patients should also be considered.Correspondence: Dr Daniela Larizza, Clinica Pediatrica, Policlinico