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.

Wolcott-Rallison syndrome (WRS) is

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.

Traditionally, idiopathic hypogonadotropic hypogonadism (IHH) is divided into two major categories: Kallmann syndrome (KS) and normosmic IHH (nIHH). To date, inactivating variants in more than 50 genes have been reported to cause IHH. These mutations are estimated to account for up to 50% of all apparently hereditary cases. Identification of further causative gene mutations is expected to be more feasible with the increasing use of whole exome/genome sequencing. Presence of more than one IHH-associated mutant gene in a given patient/pedigree (oligogenic inheritance) is seen in 10-20% of all IHH cases. It is now well established that about 10-20% of IHH cases recover from IHH either spontaneously or after receiving some sex steroid replacement therapy. Moreover, there may be an overlap or transition between constitutional delay in growth and puberty (CDGP) and IHH. It has been increasingly observed that oligogenic inheritance and clinical recovery complicates the phenotype/genotype relationship in IHH, thus making it challenging to find new IHH-associated genes. In a clinical sense, recognizing those IHH genes and associated phenotypes may improve our diagnostic capabilities by enabling us to prioritize the screening of particular gene(s) such as synkinesia (ANOS1), dental agenesis (FGF8/FGFR1) and hearing loss (CHD7). Also, IHH-associated gene studies may be translated into new therapies such as for polycystic ovary syndrome. In a scientific sense, the most significant contribution of IHH-associated gene studies has been the characterization of the long-sought gonadotropin releasing hormone pulse generator. It appears that genetic studies of IHH will continue to advance our knowledge in both the biological and clinical domains.

The protease fibroblast activation protein (FAP) is a specific marker of activated mesenchymal cells in tumour stroma and fibrotic liver. A specific, reliable FAP enzyme assay has been lacking. FAP's unique and restricted cleavage of the post proline bond was exploited to generate a new specific substrate to quantify FAP enzyme activity. This sensitive assay detected no FAP activity in any tissue or fluid of FAP gene knockout mice, thus confirming assay specificity. Circulating FAP activity was ∼20- and 1.3-fold less in baboon than in mouse and human plasma, respectively. Serum and plasma contained comparable FAP activity. In mice, the highest levels of FAP activity were in uterus, pancreas, submaxillary gland and skin, whereas the lowest levels were in brain, prostate, leukocytes and testis. Baboon organs high in FAP activity included skin, epididymis, bladder, colon, adipose tissue, nerve and tongue. FAP activity was greatly elevated in tumours and associated lymph nodes and in fungal-infected skin of unhealthy baboons. FAP activity was 14- to 18-fold greater in cirrhotic than in non-diseased human liver, and circulating FAP activity was almost doubled in alcoholic cirrhosis. Parallel DPP4 measurements concorded with the literature, except for the novel finding of high DPP4 activity in bile. The new FAP enzyme assay is the first to be thoroughly characterised and shows that FAP activity is measurable in most organs and at high levels in some. This new assay is a robust tool for specific quantitation of FAP enzyme activity in both preclinical and clinical samples, particularly liver fibrosis.

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.

SummaryThe complex organization and regulation of the human hypothalamic-pituitary-gonadal axis render it susceptible to dysfunction in the face of a variety of genetic insults, leading to different degrees of hypogonadotrophic hypogonadism (HH). Although the genetic basis of some HH was recognized more than 60 years ago the first specific pathogenic defect, in the KAL1 gene, was only identified within the last 20 years. In the past decade, the rate of genetic discovery has dramatically accelerated, with defects in more than 10 genes now associated with HH. Several themes have emerged as the genetic basis of HH has gradually been uncovered, including the association of some genes such as FGFR1, FGF8, PROK2 and PROKR2, both with HH in association with hyposmia/anosmia (Kallmann syndrome) and with normosmic HH, thus blurring the clinical distinction between ontogenic and purely functional defects in the axis. Many examples of digenic inheritance of HH have also been reported, sometimes producing variable reproductive and accessory phenotypes within a family with non-Mendelian inheritance patterns. In strictly normosmic HH, human genetics has made a particularly dramatic impact in the past 6 years through homozygosity mapping in consanguineous families, first through identification of a key role for kisspeptin in triggering GnRH release, and very recently through demonstration of a critical role for neurokinin B in normal sexual maturation. This review summarises current understanding of the genetic architecture of HH, as well as its diagnostic and mechanistic implications.