Holoprosencephaly (HPE) is a developmental defect of the embryonic forebrain and midface. It is due to the non-cleavage of the embryonic forebrain into two cerebral hemispheres and the incomplete development of the paramedian structures. The overall prevalence is 1.31 per 10,000 births. The aetiology could be genetic, environmental, or both. HPE is classified into alobar, semilobar, and lobar subtypes based on the degree of separation of the cerebral hemispheres. We report two new cases of semilobar HPE with neurogenic hypernatraemia. Lack of thirst and hypodypsia associated with chronic hypernatraemia in patients with HPE is highly suggestive of neurogenic hypernatraemia. Early identification of neurogenic hypernatraemia is important as it improves with forced fluid therapy and does not require any medication.
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