High prevalence of syndromic disorders in patients with non-isolated central precocious puberty.

Objective Non-idiopathic CPP is caused by acquired or congenital hypothalamic lesions visible on MRI or is associated with various complex genetic and/or syndromic disorders. This study investigated the different types and prevalence of non-isolated CPP phenotypes. Design and Methods This observational cohort study included all patients identified as having non-idiopathic CPP in the database of a single academic pediatric care center over a period of 11.5 years. Patients were classified on the basis of MRI findings for the CNS as having either hypothalamic lesions or complex syndromic phenotypes without structural lesions of the hypothalamus. Results In total, 63 consecutive children (42 girls and 21 boys) with non-isolated CPP were identified. Diverse diseases were detected, and the hypothalamic lesions visible on MRI (n = 28, 45% of cases) included hamartomas (n = 17; either isolated or with an associated syndromic phenotype), optic gliomas (n = 8; with or without neurofibromatosis type 1), malformations (n = 3) with interhypothalamic adhesions (n = 2; isolated or associated with syndromic CNS midline abnormalities, such as optic nerve hypoplasia, ectopic posterior pituitary) or arachnoid cysts (n = 1). The patients with non-structural hypothalamic lesions (n = 35, 55% of cases) had narcolepsy (n = 9), RASopathies (n = 4), encephalopathy or autism spectrum disorders with or without chromosomal abnormalities (n = 15) and other complex syndromic disorders (n = 7). Conclusion Our findings suggest that a large proportion (55%) of patients with non-isolated probable non-idiopathic CPP may have complex disorders without structural hypothalamic lesions on MRI. Future studies should explore the pathophysiological relevance of the mechanisms underlying CPP in these disorders.

Haploinsufficiency of Dmxl2, encoding a synaptic protein, causes infertility associated with a loss of GnRH neurons in mouse.

Characterization of the genetic defects causing gonadotropic deficiency has made a major contribution to elucidation of the fundamental role of Kisspeptins and Neurokinin B in puberty onset and reproduction. The absence of puberty may also reveal neurodevelopmental disorders caused by molecular defects in various cellular pathways. Investigations of these neurodevelopmental disorders may provide information about the neuronal processes controlling puberty onset and reproductive capacity. We describe here a new syndrome observed in three brothers, which involves gonadotropic axis deficiency, central hypothyroidism, peripheral demyelinating sensorimotor polyneuropathy, mental retardation, and profound hypoglycemia, progressing to nonautoimmune insulin-dependent diabetes mellitus. High-throughput sequencing revealed a homozygous in-frame deletion of 15 nucleotides in DMXL2 in all three affected patients. This homozygous deletion was associated with lower DMXL2 mRNA levels in the blood lymphocytes of the patients. DMXL2 encodes the synaptic protein rabconnectin-3α, which has been identified as a putative scaffold protein for Rab3-GAP and Rab3-GEP, two regulators of the GTPase Rab3a. We found that rabconnectin-3α was expressed in exocytosis vesicles in gonadotropin-releasing hormone (GnRH) axonal extremities in the median eminence of the hypothalamus. It was also specifically expressed in cells expressing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) within the pituitary. The conditional heterozygous deletion of Dmxl2 from mouse neurons delayed puberty and resulted in very low fertility. This reproductive phenotype was associated with a lower number of GnRH neurons in the hypothalamus of adult mice. Finally, Dmxl2 knockdown in an insulin-secreting cell line showed that rabconnectin-3α controlled the constitutive and glucose-induced secretion of insulin. In conclusion, this study shows that low levels of DMXL2 expression cause a complex neurological phenotype, with abnormal glucose metabolism and gonadotropic axis deficiency due to a loss of GnRH neurons. Our findings identify rabconectin-3α as a key controller of neuronal and endocrine homeostatic processes.

Different mechanisms of intestinal calcium absorption at different life stages: therapeutic implications and long-term responses to treatment in patients with hereditary vitamin D-resistant rickets.

BACKGROUND: Intestinal calcium absorption is regulated principally by 1,25-dihydroxyvitamin D, but other regulators are also involved. CASE REPORT: The 3 children studied were born with unaffected bones. Two were referred at 21 months of age, with clinical features of severe vitamin D-resistant rickets. They were treated with intravenous calcium for 12-18 months, following an initial lack of response to oral calcium and vitamin D. The third patient, who was exclusively breast-fed, was diagnosed at 4 months of age, due to alopecia. His condition was successfully managed with high doses of oral calcium and vitamin D. All 3 patients were homozygous for a mutation in the DNA-binding domain of vitamin D receptor. At the most recent evaluation of these patients, currently maintained on oral calcium and vitamin D, clinical findings were normal. CONCLUSION: During gestation, calcium flux across the placenta is normal, preventing bone diseases in affected fetuses. High calcium intake early in life and, perhaps, the maintenance of breastfeeding for several months may constitute an effective approach to ensuring adequate absorption and preventing severe rickets. During childhood, after parenteral calcium treatment to bypass intestinal calcium absorption, it is possible to maintain normal bone through long-term oral calcium supplementation.