New Features in a Rare Monogenic Obesity: Carboxypeptidase E Deficiency

Carboxypeptidase E (CPE) is an enzyme involved in the neuropeptides/hormones processing. Its deficiency is associated with endocrinopathies comparable to those caused by proprotein convertase 1/3(PC1/3) deficiency. In this case report, we expand the clinical features of CPE deficiency by examining the index case's clinical/laboratory results, which are also indicative of PC1/3 deficiency.

The index case, 13.5 years old, had obesity, central hypothyroidism, developmental delay, hypogonadotropic hypogonadism, enuresis. A 4-hour oral glucose tolerance test revealed glucose intolerance with a partial insulin deficiency and postprandial hypoglycemia. Proinsulin level was high. Partial central diabetes insipidus was verified with a water deprivation test. Administration of desmopressin successfully alleviated the symptoms of polyuria-polydipsia and enuresis. Brain-derived-neurotrophic-factor level, which might be linked to ID, was low. The 8-month-old sibling had central hypothyroidism and hypotonicity but has not yet developed obesity.

Patients with CPE deficiency should undergo evaluation not only for hypothyroidism and hypogonadism but also for glucose and water metabolism disorders. The presentation of new cases may lead to the discovery of novel findings, and the identification of other pituitary hormone deficiencies.