The timely secretion of gonadal sex steroids is essential for the initiation of puberty, the postpubertal maintenance of secondary sexual characteristics and the normal perinatal development of male external genitalia. Normal gonadal steroid production requires the actions of the pituitary-derived gonadotropins, luteinizing hormone and follicle-stimulating hormone. We report four human pedigrees with severe congenital gonadotropin deficiency and pubertal failure in which all affected individuals are homozygous for loss-of-function mutations in TAC3 (encoding Neurokinin B) or its receptor TACR3 (encoding NK3R). Neurokinin B, a member of the substance P-related tachykinin family, is known to be highly expressed in hypothalamic neurons that also express kisspeptin, a recently identified regulator of gonadotropin-releasing hormone secretion. These findings implicate Neurokinin B as a critical central regulator of human gonadal function and suggest new approaches to the pharmacological control of human reproduction and sex hormone-related diseases.

SUM M A R YGonadotropin-releasing hormone (GnRH) is the central regulator of gonadotropins, which stimulate gonadal function. Hypothalamic neurons that produce kisspeptin and neurokinin B stimulate GnRH release. Inactivating mutations in the genes encoding the human kisspeptin receptor (KISS1R, formerly called GPR54), neurokinin B (TAC3), and the neurokinin B receptor (TACR3) result in pubertal failure. However, human kisspeptin loss-of-function mutations have not been described, and contradictory findings have been reported in Kiss1-knockout mice. We describe an inactivating mutation in KISS1 in a large consanguineous family that results in failure of pubertal progression, indicating that functional kisspeptin is important for puberty and reproduction in humans. I t is still unknown how puberty in humans, occurring during the early years of the second decade of life, is initiated. 1 The hallmark of puberty is increased secretion of the gonadotropins, luteinizing hormone (LH) and folliclestimulating hormone (FSH), which act in concert to stimulate the gonads to drive sex-hormone secretion and gametogenesis. The production of gonadotropins from pituitary gonadotropic cells is controlled by the pulsatile delivery of GnRH. Inactivating mutations in the genes encoding GNRH1 2 or the GNRH receptor (GNRHR) 3 give rise to normosmic idiopathic hypogonadotropic hypogonadism in humans. 4 However, GnRH neurons lack sex-steroid receptors. This suggests the existence of GnRH-regulating neurons, which would mediate this effect.A major breakthrough in identifying such candidate neurons was the finding that inactivating mutations in genes encoding the human kisspeptin receptor (KISS1R, formerly called GPR54), the cognate receptor for a hypothalamic peptide, kisspeptin, resulted in pubertal failure. 4,5 More recently, mutations in TAC3 or TACR3 (encoding neurokinin B and its receptor, respectively) were shown to result in the same phenotype. 6 Kisspeptin and neurokinin B are coexpressed, along with dynorphin, in sex-hormone-responsive neurons in the arcuate nucleus (infundibular nucleus in primates), and their coordinated activity appears to regulate GnRH secretion. 7 Gene defects associated with normosmic idiopathic hypogonadotropic hypogonadism have been described in all the neuropeptides and receptors identified as stimulators of GnRH except for the kisspeptin gene (KISS1).Although Kiss1-and Kiss1r-knockout mouse models largely produce phenocopies (i.e., affected noncarriers) of human normosmic idiopathic hypogonadotropic hypogonadism resulting from inactivating mutations of KISS1R, there is evidence of remarkable residual activity of the hypothalamic-pituitary-gonadal axis.

Premature ovarian failure (POF) is genetically heterogeneous and manifests as hypergonadotropic hypogonadism either as part of a syndrome or in isolation. We studied two unrelated consanguineous families with daughters exhibiting primary amenorrhea, short stature, and a 46,XX karyotype. A combination of SNP arrays, comparative genomic hybridization arrays, and whole-exome sequencing analyses identified homozygous pathogenic variants in MCM9, a gene implicated in homologous recombination and repair of double-stranded DNA breaks. In one family, the MCM9 c.1732+2T>C variant alters a splice donor site, resulting in abnormal alternative splicing and truncated forms of MCM9 that are unable to be recruited to sites of DNA damage. In the second family, MCM9 c.394C>T (p.Arg132(∗)) results in a predicted loss of functional MCM9. Repair of chromosome breaks was impaired in lymphocytes from affected, but not unaffected, females in both families, consistent with MCM9 function in homologous recombination. Autosomal-recessive variants in MCM9 cause a genomic-instability syndrome associated with hypergonadotropic hypogonadism and short stature. Preferential sensitivity of germline meiosis to MCM9 functional deficiency and compromised DNA repair in the somatic component most likely account for the ovarian failure and short stature.

SUM M A R YGonadotropin-releasing hormone (GnRH) is the central regulator of gonadotropins, which stimulate gonadal function. Hypothalamic neurons that produce kisspeptin and neurokinin B stimulate GnRH release. Inactivating mutations in the genes encoding the human kisspeptin receptor (KISS1R, formerly called GPR54), neurokinin B (TAC3), and the neurokinin B receptor (TACR3) result in pubertal failure. However, human kisspeptin loss-of-function mutations have not been described, and contradictory findings have been reported in Kiss1-knockout mice. We describe an inactivating mutation in KISS1 in a large consanguineous family that results in failure of pubertal progression, indicating that functional kisspeptin is important for puberty and reproduction in humans. I t is still unknown how puberty in humans, occurring during the early years of the second decade of life, is initiated. 1 The hallmark of puberty is increased secretion of the gonadotropins, luteinizing hormone (LH) and folliclestimulating hormone (FSH), which act in concert to stimulate the gonads to drive sex-hormone secretion and gametogenesis. The production of gonadotropins from pituitary gonadotropic cells is controlled by the pulsatile delivery of GnRH. Inactivating mutations in the genes encoding GNRH1 2 or the GNRH receptor (GNRHR) 3 give rise to normosmic idiopathic hypogonadotropic hypogonadism in humans. 4 However, GnRH neurons lack sex-steroid receptors. This suggests the existence of GnRH-regulating neurons, which would mediate this effect.A major breakthrough in identifying such candidate neurons was the finding that inactivating mutations in genes encoding the human kisspeptin receptor (KISS1R, formerly called GPR54), the cognate receptor for a hypothalamic peptide, kisspeptin, resulted in pubertal failure. 4,5 More recently, mutations in TAC3 or TACR3 (encoding neurokinin B and its receptor, respectively) were shown to result in the same phenotype. 6 Kisspeptin and neurokinin B are coexpressed, along with dynorphin, in sex-hormone-responsive neurons in the arcuate nucleus (infundibular nucleus in primates), and their coordinated activity appears to regulate GnRH secretion. 7 Gene defects associated with normosmic idiopathic hypogonadotropic hypogonadism have been described in all the neuropeptides and receptors identified as stimulators of GnRH except for the kisspeptin gene (KISS1).Although Kiss1-and Kiss1r-knockout mouse models largely produce phenocopies (i.e., affected noncarriers) of human normosmic idiopathic hypogonadotropic hypogonadism resulting from inactivating mutations of KISS1R, there is evidence of remarkable residual activity of the hypothalamic-pituitary-gonadal axis.

Homozygosity for the TACR3 His148Leu mutation leads to failure of sexual maturation in humans, whereas signaling by the mutant receptor in vitro in response to either NKB or senktide is severely impaired. These observations further strengthen the link between NKB, the NKB receptor, and regulation of human reproductive function.

Altered Bone Morphogenetic Protein (BMP) signaling leads to multiple developmental defects, including brachydactyly and deafness. Here we identify chondroitin synthase 1 (CHSY1) as a potential mediator of BMP effects. We show that loss of human CHSY1 function causes autosomal-recessive Temtamy preaxial brachydactyly syndrome (TPBS), mainly characterized by limb malformations, short stature, and hearing loss. After mapping the TPBS locus to chromosome 15q26-qterm, we identified causative mutations in five consanguineous TPBS families. In zebrafish, antisense-mediated chsy1 knockdown causes defects in multiple developmental processes, some of which are likely to also be causative in the etiology of TPBS. In the inner ears of zebrafish larvae, chsy1 is expressed similarly to the BMP inhibitor dan and in a complementary fashion to bmp2b. Furthermore, unrestricted Bmp2b signaling or loss of Dan activity leads to reduced chsy1 expression and, during epithelial morphogenesis, defects similar to those that occur upon Chsy1 inactivation, indicating that Bmp signaling affects inner-ear development by repressing chsy1. In addition, we obtained strikingly similar zebrafish phenotypes after chsy1 overexpression, which might explain why, in humans, brachydactyly can be caused by mutations leading either to loss or to gain of BMP signaling.

Wolcott-Rallison syndrome (WRS) is a rare autosomal recessive disorder characterized by an early-infancy-onset diabetes mellitus associated with a variety of multisystemic clinical manifestations. Here, we present six patients with WRS, carrying the same homozygous mutation (EIF2AK3-W522X), from two unrelated Turkish families. This is the largest series of patients with the same mutation for this rare syndrome. In this communication we compare clinical features of these six patients with the other 34 patients who have been reported to date, and review the clinical features of WRS. All WRS patients presented first with symptoms of insulin dependent diabetes mellitus, with a mean age at onset of 2 months. All patients had skeletal dysplasia or early signs of it, and growth retardation. Many of the patients with WRS have been reported to have developmental delay, mental retardation, and learning difficulties; in contrast, none of our patients showed abnormal development at age up to 30 months. Acute attacks of hepatic failure were reported in 23 cases out of 37 patients; in 15 of those 23 cases an acute attack of renal failure accompanied the liver failure. Exocrine pancreatic deficiency has been reported in only four cases other than our four patients. Central hypothyroidism was observed in six of 28 cases. We propose that central hypothyroidism is not a component of WRS, but rather a reflection of euthyroid sick syndrome. Four of our patients experienced severe neutropenia, compared to only five of the 27 other cases, suggesting that the W522X mutation may be specifically associated with neutropenia. Other than the consistent features of diabetes mellitus and epiphyseal dysplasia, WRS patients are otherwise characterized by extensive phenotypic variability that correlates poorly to genotype.

These results suggest that NTE-dependent alteration of phospholipid homeostasis in GHS causes both neurodegeneration and impaired LH release from pituitary gonadotropes, leading to nHH.