Elka Jacobson-Dickman

Decreased FGF8 signaling causes deficiency of gonadotropin-releasing hormone in humans and mice

Idiopathic hypogonadotropic hypogonadism (IHH) with anosmia (Kallmann syndrome; KS) or with a normal sense of smell (normosmic IHH; nIHH) are heterogeneous genetic disorders associated with deficiency of gonadotropin-releasing hormone (GnRH). While loss-of-function mutations in FGF receptor 1 (FGFR1) cause human GnRH deficiency, to date no specific ligand for FGFR1 has been identified in GnRH neuron ontogeny. Using a candidate gene approach, we identified 6 missense mutations in FGF8 in IHH probands with variable olfactory phenotypes. These patients exhibited varied degrees of GnRH deficiency, including the rare adult-onset form of hypogonadotropic hypogonadism. Four mutations affected all 4 FGF8 splice isoforms (FGF8a, FGF8b, FGF8e, and FGF8f), while 2 mutations affected FGF8e and FGF8f isoforms only. The mutant FGF8b and FGF8f ligands exhibited decreased biological activity in vitro. Furthermore, mice homozygous for a hypomorphic Fgf8 allele lacked GnRH neurons in the hypothalamus, while heterozygous mice showed substantial decreases in the number of GnRH neurons and hypothalamic GnRH peptide concentration. In conclusion, we identified FGF8 as a gene implicated in GnRH deficiency in both humans and mice and demonstrated an exquisite sensitivity of GnRH neuron development to reductions in FGF8 signaling.

Loss-of-function mutation in the prokineticin 2 gene causes Kallmann syndrome and normosmic idiopathic hypogonadotropic hypogonadism.

Gonadotropin-releasing hormone (GnRH) deficiency in the human presents either as normosmic idiopathic hypogonadotropic hypogonadism (nIHH) or with anosmia [Kallmann syndrome (KS)]. To date, several loci have been identified to cause these disorders, but only 30% of cases exhibit mutations in known genes. Recently, murine studies have demonstrated a critical role of the prokineticin pathway in olfactory bulb morphogenesis and GnRH secretion. Therefore, we hypothesize that mutations in prokineticin 2 (PROK2) underlie some cases of KS in humans and that animals deficient in Prok2 would be hypogonadotropic. One hundred IHH probands (50 nIHH and 50 KS) with no known mutations were examined for mutations in the PROK2 gene. Mutant PROK2s were examined in functional studies, and the reproductive phenotype of the Prok2−/− mice was also investigated. Two brothers with KS and their sister with nIHH harbored a homozygous deletion in the PROK2 gene (p.[I55fsX1]+[I55fsX1]). Another asymptomatic brother was heterozygous for the deletion, whereas both parents (deceased) had normal reproductive histories. The identified deletion results in a truncated PROK2 protein of 27 amino acids (rather than 81 in its mature form) that lacks bioactivity. In addition, Prok2−/− mice with olfactory bulb defects exhibited disrupted GnRH neuron migration, resulting in a dramatic decrease in GnRH neuron population in the hypothalamus as well as hypogonadotropic hypogonadism. Homozygous loss-of-function PROK2 mutations cause both KS and nIHH.

Vitamin D Supplementation and Risk of Toxicity in Pediatrics: A Review of Current Literature

CONTEXT Although vitamin D toxicity is rare in children, increased use of vitamin D formulations, re-examination of optimal vitamin D levels, and use of higher doses lend potential for an increased incidence of vitamin D toxicity. EVIDENCE ACQUISITION A PubMed search was conducted through May 2013 for cases of vitamin D intoxication and vitamin D trials in pediatrics. Safety data were collected and reviewed. EVIDENCE SYNTHESIS A small number of pediatric studies tested vitamin D doses at or above the currently recommended upper tolerable intake. In children and adolescents, vitamin D excess was rare and usually asymptomatic. Recent cases of intoxication relate to errors in manufacturing, formulation, or prescription; involve high total intake in the range of 240,000 to 4,500,000 IU; and present with severe hypercalcemia, hypercalciuria, or nephrocalcinosis. However, mild hypercalcemia and hypervitaminosis using currently recommended doses have been reported in infants with rickets. CONCLUSIONS Although rare, cases of vitamin D intoxication that present with dramatic life-threatening symptoms still occur in children. Moreover, recent studies in infants raise a potential need for monitoring vitamin D levels when doses at or above the currently recommended upper range are used. Further studies are needed to clarify these findings. The Drugs and Therapeutics Committee of the Pediatric Endocrine Society suggests obtaining serum 25-hydroxyvitamin D levels in infants and children who receive long-term vitamin D supplementation at or above the upper level intake that is currently recommended.

Congenital hypogonadotropic hypogonadism with split hand/foot malformation: a clinical entity with a high frequency of FGFR1 mutations

Purpose:Congenital hypogonadotropic hypogonadism (CHH) and split hand/foot malformation (SHFM) are two rare genetic conditions. Here we report a clinical entity comprising the two.Methods:We identified patients with CHH and SHFM through international collaboration. Probands and available family members underwent phenotyping and screening for FGFR1 mutations. The impact of identified mutations was assessed by sequence- and structure-based predictions and/or functional assays.Results:We identified eight probands with CHH with (n = 3; Kallmann syndrome) or without anosmia (n = 5) and SHFM, seven of whom (88%) harbor FGFR1 mutations. Of these seven, one individual is homozygous for p.V429E and six individuals are heterozygous for p.G348R, p.G485R, p.Q594*, p.E670A, p.V688L, or p.L712P. All mutations were predicted by in silico analysis to cause loss of function. Probands with FGFR1 mutations have severe gonadotropin-releasing hormone deficiency (absent puberty and/or cryptorchidism and/or micropenis). SHFM in both hands and feet was observed only in the patient with the homozygous p.V429E mutation; V429 maps to the fibroblast growth factor receptor substrate 2α binding domain of FGFR1, and functional studies of the p.V429E mutation demonstrated that it decreased recruitment and phosphorylation of fibroblast growth factor receptor substrate 2α to FGFR1, thereby resulting in reduced mitogen-activated protein kinase signaling.Conclusion:FGFR1 should be prioritized for genetic testing in patients with CHH and SHFM because the likelihood of a mutation increases from 10% in the general CHH population to 88% in these patients.Genet Med 17 8, 651–659.

An ancient founder mutation in PROKR2 impairs human reproduction

Congenital gonadotropin-releasing hormone (GnRH) deficiency manifests as absent or incomplete sexual maturation and infertility. Although the disease exhibits marked locus and allelic heterogeneity, with the causal mutations being both rare and private, one causal mutation in the prokineticin receptor, PROKR2 L173R, appears unusually prevalent among GnRH-deficient patients of diverse geographic and ethnic origins. To track the genetic ancestry of PROKR2 L173R, haplotype mapping was performed in 22 unrelated patients with GnRH deficiency carrying L173R and their 30 first-degree relatives. The mutations age was estimated using a haplotype-decay model. Thirteen subjects were informative and in all of them the mutation was present on the same ~123 kb haplotype whose population frequency is ≤10%. Thus, PROKR2 L173R represents a founder mutation whose age is estimated at approximately 9000 years. Inheritance of PROKR2 L173R-associated GnRH deficiency was complex with highly variable penetrance among carriers, influenced by additional mutations in the other PROKR2 allele (recessive inheritance) or another gene (digenicity). The paradoxical identification of an ancient founder mutation that impairs reproduction has intriguing implications for the inheritance mechanisms of PROKR2 L173R-associated GnRH deficiency and for the relevant processes of evolutionary selection, including potential selective advantages of mutation carriers in genes affecting reproduction.

A teenage boy with hypocalcemia after radioablation for Graves' disease

Abstract Excessive thyroid hormone production, as seen in Graves’ disease, stimulates osteoblast-mediated bone turnover in favor of bone resorption. Acute reversal of bone resorption can lead to hungry bone syndrome (HBS), a state of rapid calcium deposition into newly synthesized osteoid resulting in hypocalcemia. Hypocalcemia due to subsequent functional or relative hypoparathyroidism is a recognized complication of therapy for Graves’ disease. HBS is most recognized as an outcome of rapid correction of vitamin D deficiency or of acute hypoparathyroidism in cases of parathyroid gland function disruption after surgical removal of the thyroid. We report the case of an adolescent boy with Graves’ disease who presented with hypocalcemia after radioactive iodine (131I) therapy due to HBS. Our report highlights the risk of HBS and severe hypocalcemia following treatment for Graves’ disease in pediatric patients and also underscores the importance of pretreatment assessment and intervention for coexistent vitamin D deficiency.

Impaired Fibroblast Growth Factor Receptor 1 Signaling as a Cause of Normosmic Idiopathic Hypogonadotropic Hypogonadism

The Harvard Center for Reproductive Endocrine Sciences and the Reproductive Endocrine Unit of the Department of Medicine (T.R., Y.S., L.P., A.M., E.J.-D., V.A.H., A.D., F.J.H., N.P.), Massachusetts General Hospital, and Harvard Center for Reproductive Endocrine Sciences and Brigham and Women’s Hospital (S.X., U.B.K.), Division of Endocrinology, Diabetes, and Hypertension, Boston, Massachusetts 02114; Department of Pharmacology (H.C., J.M., M.M.), New York University School of Medicine, New York, New York 10016; Institute of Human Genetics (R.Q.), University of Newcastle-upon-Tyne, Newcastle NE2 4HH, United Kingdom; Sainte Justin Hospital (G.V.V.), Montreal, Quebec, Canada H3T 1C5; Centre Hospitalier de l’Universite de Montreal and Procrea Cliniques (H.L.), Montreal, Quebec, Canada H2W1T8; Department of Genetics and Metabolism (S.S.), Children’s National Medical Center, Washington, DC 20010; and Biomedicum Helsinki (T.R.), Institute of Biomedicine/Physiology, University of Helsinki, FIN-00014 Helsinki, Finland