ObjectiveCongenital hypogonadotropic hypogonadism (CHH) and constitutional delay of growth and puberty (CDGP) represent rare and common forms of GnRH deficiency, respectively. Both CDGP and CHH present with delayed puberty, and the distinction between these two entities during early adolescence is challenging. More than 30 genes have been implicated in CHH, while the genetic basis of CDGP is poorly understood.DesignWe characterized and compared the genetic architectures of CHH and CDGP, to test the hypothesis of a shared genetic basis between these disorders.MethodsExome sequencing data were used to identify rare variants in known genes in CHH (n = 116), CDGP (n = 72) and control cohorts (n = 36 874 ExAC and n = 405 CoLaus).ResultsMutations in at least one CHH gene were found in 51% of CHH probands, which is significantly higher than in CDGP (7%, P = 7.6 × 10−11) or controls (18%, P = 5.5 × 10−12). Similarly, oligogenicity (defined as mutations in more than one gene) was common in CHH patients (15%) relative to CDGP (1.4%, P = 0.002) and controls (2%, P = 6.4 × 10−7).ConclusionsOur data suggest that CDGP and CHH have distinct genetic profiles, and this finding may facilitate the differential diagnosis in patients presenting with delayed puberty.

Familial hypobetalipoproteinemia includes a heterogeneous group of inherited disorders of lipid metabolism typically characterized by very low levels (below the 5th percentile of age-and sex-specifi c values) of plasma low density lipoprotein cholesterol (LDL-C) and/or apo B ( 1, 2 ). Beside the very rare recessive disorder abetalipoproteinemia (ABL, OMIM # 200100) caused by mutation in the gene coding for the microsomal triglyceride transfer protein ( MTP ), the best-characterized cases are those with Press, September 19, 2013 DOI 10.1194 Clinical characteristics and plasma lipids in subjects with familial combined hypolipidemia: a pooled analysis Abbreviations: ANGPTL3, angiopoietin-like 3; BMI, body mass index; FBG, fasting blood glucose; FHBL, familial hypobetalipoproteinemia; FHBL2, familial combined hypolipidemia; FLI, fatty liver index; ␥ -GT, ␥ -glutamyltranspeptidase; GFR, glomerular fi ltration rate; Lp(a), lipoprotein(a); TG, triglyceride . ); National Institutes of Health Grant K08-HL-114642 (to N.S.); Massachusetts General Hospital (MGH) Research Scholar Award and Howard Goodman Fellowship (to S.K.); Donovan Family Foundation Grant (to S.K.), National Institutes of Health Grant R01 HL-107816 (to S.K.); and Fondation Leducq Grant (to S.K.). Manuscript received 7 May 2013 and in revised form 17 September 2013. Published, JLR Papers in

Congenital hypogonadotropic hypogonadism (CHH) is a rare genetic disorder characterized by infertility and the absence of puberty. Defects in GnRH neuron migration or altered GnRH secretion and/or action lead to a severe gonadotropin-releasing hormone (GnRH) deficiency. Given the close developmental association of GnRH neurons with the olfactory primary axons, CHH is often associated with anosmia or hyposmia, in which case it is defined as Kallmann syndrome (KS). The genetics of CHH are heterogeneous, and >40 genes are involved either alone or in combination. Several CHH-related genes controlling GnRH ontogeny encode proteins containing fibronectin-3 (FN3) domains, which are important for brain and neural development. Therefore, we hypothesized that defects in other FN3-superfamily genes would underlie CHH. Next-generation sequencing was performed for 240 CHH unrelated probands and filtered for rare, protein-truncating variants (PTVs) in FN3-superfamily genes. Compared to gnomAD controls the CHH cohort was statistically enriched for PTVs in neuron-derived neurotrophic factor (NDNF) (p ¼ 1.40 3 10 À6 ). Three heterozygous PTVs (p.Lys62*, p.Tyr128Thrfs*55, and p.Trp469*, all absent from the gnomAD database) and an additional heterozygous missense mutation (p.Thr201Ser) were found in four KS probands. Notably, NDNF is expressed along the GnRH neuron migratory route in both mouse embryos and human fetuses and enhances GnRH neuron migration. Further, knock down of the zebrafish ortholog of NDNF resulted in altered GnRH migration. Finally, mice lacking Ndnf showed delayed GnRH neuron migration and altered olfactory axonal projections to the olfactory bulb; both results are consistent with a role of NDNF in GnRH neuron development. Altogether, our results highlight NDNF as a gene involved in the GnRH neuron migration implicated in KS.

Congenital hypogonadotropic hypogonadism (CHH) is a rare genetic disease characterized by absent puberty and infertility due to GnRH deficiency, and is often associated with anosmia [Kallmann syndrome (KS)]. The genetic etiology of CHH is heterogeneous, and more than 30 genes have been implicated in approximately 50% of patients with CHH. We hypothesized that genes encoding axon-guidance proteins containing fibronectin type-III (FN3) domains (similar to ANOS1, the first gene associated with KS), are mutated in CHH. We performed whole-exome sequencing in a cohort of 133 CHH probands to test this hypothesis, and identified rare sequence variants (RSVs) in genes encoding for the FN3-domain encoding protein deleted in colorectal cancer (DCC) and its ligand Netrin-1 (NTN1). In vitro studies of these RSVs revealed altered intracellular signaling associated with defects in cell morphology, and confirmed five heterozygous DCC mutations in 6 probands-5 of which presented as KS. Two KS probands carry heterozygous mutations in both DCC and NTN1 consistent with oligogenic inheritance. Further, we show that Netrin-1 promotes migration in immortalized GnRH neurons (GN11 cells). This study implicates DCC and NTN1 mutations in the pathophysiology of CHH consistent with the role of these two genes in the ontogeny of GnRH neurons in mice.