The hallmarks of the X-linked alpha-thalassemia/mental retardation (ATR-X) syndrome are severe psychomotor retardation, minor facial anomalies, genital abnormalities, and an unusual form of alpha-thalassemia. The demonstration of HbH inclusions in red blood cells after incubation with brilliant cresyl blue confirms the diagnosis. We describe 15 previously unreported cases and analyse the phenotypic and hematologic findings in these subjects and compare them with previously published cases. This study demonstrates the consistency of the main characteristics of this syndrome and extends the phenotype. Developmental changes in phenotype, in particular the coarsening of the facial appearance, are illustrated. The hematologic findings are shown to vary widely; in some cases the manifestation of alpha-thalassemia may be subtle and missed without repeated examination.

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We describe a 24-year-old short, obese girl who has bizarre episodic neurological abnormalities related to hyperosmolality due to hypernatraemia. Investigation of osmoregulation by water loading and infusion of hypertonic saline revealed (i) hypodipsia with thirst onset raised to plasma osmolality of 332 mmol/kg and (ii) elevation of the threshold for vasopressin release (plasma osmolality 320 mmol/kg) but normal slope of the plasma vasopressin-plasma osmolality curve. Baroregulated vasopressin release was also grossly subnormal. Other hypothalamo-pituitary investigations showed deficiencies of releasing hormones for gonadotrophins and growth hormone, but prolactin response to combined hypoglycaemia and TRH was blunted She demonstrated other anomalies including hyperlipoproteinaemia and defective lymph drainage of the legs. Skull X-rays, together with computerized tomography and nuclear magnetic resonance scans of the hypothalamo-pituitary region and the rest of the brain were normal. We believe that this is the first case of essential hypernatraemia documented with direct evidence of resetting of the osmostat.

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