Genetics and hypogonadotrophic hypogonadism

Single-Nucleotide Variations of the Human Nuclear Hormone Receptor Genes in 60,000 Individuals

Nuclear hormone receptors (NRs) mediate biologic actions of lipophilic molecules to gene transcription and are phylogenetically and functionally categorized into seven subfamilies and three groups, respectively. Single-nucleotide variations (SNVs) or polymorphisms are genetic changes influencing individual response to environmental factors and susceptibility to various disorders, and are part of the genetic diversification and basis for evolution. We sorted out SNVs of the human NR genes from 60,706 individuals, calculated three parameters (percentage of all variants, percentage of loss-of-function variants, and ratio of nonsynonymous/synonymous variants in their full protein-coding or major domain-coding sequences), and compared them with several valuables. Comparison of these parameters between NRs and control groups identified that NRs form a highly conserved gene family. The three parameters for the full coding sequence are positively correlated with each other, whereas four NR genes are distinct from the others with much higher tolerance to protein sequence-changing variants. DNA-binding domain and N-terminal domain are respectively those bearing the least and the most variation. NR subfamilies based on their phylogenetic proximity or functionality as well as diversity of tissue distribution and numbers of partner molecules are all not correlated with the variation parameters, whereas their gene age demonstrates an association. Our results suggest that the natural selection driving the NR family evolution still operates in humans. Gene age and probably the potential to adapt to various new ligands, but not current functional diversity, are major determinants for SNVs of the human NR genes.

Diversity in fibroblast growth factor receptor 1 regulation: learning from the investigation of Kallmann syndrome

The unravelling of the genetic basis of the hypogonadotrophic hypogonadal disorders, including Kallmann syndrome (KS), has led to renewed interest into the developmental biology of gonadotrophin-releasing hormone (GnRH) neurones and, more generally, into the molecular mechanisms of reproduction. KS is characterised by the association of GnRH deficiency with diminished olfaction. Until recently, only two KS-associated genes were known: KAL1 and KAL2. KAL1 encodes the cell membrane and extracellular matrix-associated secreted protein anosmin-1 which is implicated in the X-linked form of KS. Anosmin-1 shows high affinity binding to heparan sulphate (HS) and its function remains the focus of ongoing investigation, although a role in axonal guidance and neuronal migration, which are processes essential for normal GnRH ontogeny and olfactory bulb histogenesis, has been suggested. KAL2, identified as the fibroblast growth factor receptor 1 (FGFR1) gene, has now been recognised to be the underlying genetic defect for an autosomal dominant form of KS. The diverse signalling pathways initiated upon FGFR activation can elicit pleiotropic cellular responses depending on the cellular context. Signalling through FGFR requires HS for receptor dimerisation and ligand binding. Current evidence supports a HS-dependent interaction between anosmin-1 and FGFR1, where anosmin-1 serves as a co-ligand activator enhancing the signal activity, the finer details of whose mechanism remain the subject of intense investigation. Recently, mutations in the genes encoding prokineticin 2 (PK2) and prokineticin receptor 2 (PKR2) were reported in a cohort of KS patients, further reinforcing the view of KS as a multigenic trait involving divergent pathways. Here, we review the historical and current understandings of KS and discuss the latest findings from the molecular and cellular studies of the KS-associated proteins, and describe the evidence that suggests convergence of several of these pathways during normal GnRH and olfactory neuronal ontogeny.

Clinical and inheritance profiles of Kallmann syndrome in Jordan

Background

Proper management of patients with Kallmann syndrome (KS) allows them to attain a normal reproductive health. The purpose of this study is to demonstrate the presentation modalities, phenotypes and the modes of inheritance among 32 patients with Kallmann syndrome in Jordan. Recognition of the syndrome allows for prompt proper management and provision of genetic counselling.

Subjects

Over a period of five years (1999–2004), the clinical and inheritance profiles of 26 male and 6 female patients with Kallmann syndrome from 12 families were evaluated at the National Center for Diabetes, Endocrinology and Genetics in Jordan.

Results

The patients belonged to twelve Jordanian and Palestinian families and their age at presentation ranged from 4 – 46 years. Nine boys aged 4–14 years presented with cryptorchidism and microphallus, all other males presented with delayed puberty, hypogonadism and/or infertility. The main presentation among six female patients was primary amenorrhea. Intrafamilial variability in clinical phenotype was specifically evident for renal abnormalities and sensorineural hearing impairment. Familial KS was diagnosed in 27 patients belonging to five families with the X-linked mode of inheritance and two families with the autosomal recessive mode of inheritance.

Conclusions

(1) the majority of cases in this study represented the X-linked form of KS, which might point to a high prevalence of Kal 1 gene in the population. (2) Genetic counselling helps these families to reach a diagnosis at an early age and to decide about their reproductive options. (3) Children presenting with cryptorchidism and microphallus in our population should be investigated for KS.