👤 Michihiro Tanikawa

Congenital hypogonadotropic hypogonadism (CHH) is a genetically heterogeneous disorder, with multiple causative and candidate genes identified to date. To clarify underlying genetic factors involved in the development of CHH. We examined 88 Japanese patients with CHH using gene panel analysis (GPA) for 14 representative causative genes and whole-exome sequencing (WES) which was initially focused on 41 causative/candidate genes and subsequently expanded to other genes. We extracted rare variants (frequency of <0.01) and performed pathogenic assessment using refined American College of Medical Genetics and Genomics/Association for Molecular Pathology criteria and registered information in ClinVar. Twenty-seven pathogenic/likely pathogenic variants were identified in 30 patients through GPA performed for all 88 patients and in 4 patients through WES performed for 58 patients in whom no obvious disease-causing variants were revealed by GPA. They resided in previously known ANOS1 (6 variants in 7 patients), CHD7 (3 variants in 3 patients), FGFR1 (14 variants in 15 patients), PROKR2 (2 variants in 8 patients), and SOX10 (1 variant in 1 patient), and a hitherto unrecognized ZNF462 (1 variant in 1 patient). One patient had 2 variants. Additionally, potentially CHH-related variants were detected in 12 genes including SEMA4D and CDH2 postulated on the CHH-related molecular network. Furthermore, in the 41 CHH-related genes, the frequency of oligogenicity was significantly higher and the number of rare variants per individual was significantly larger in 54 CHH patients with no discernible pathogenic/likely pathogenic variants than in 100 control individuals. The results support the notion that CHH occurs not only as a monogenic disorder but also as an oligogenic/multifactorial disorder, and suggest the involvement of ZNF462, SEMA4D, and CDH2 variants in the development of CHH. Show less

Although 17β-hydroxysteroid dehydrogenase type 3 (HSD17B3) deficiency is diagnosed when a testosterone/androstenedione (T/A-dione) ratio after human chorionic gonadotropin (hCG) stimulation is below 0.8, this cut-off value is primarily based on hormonal data measured by conventional immunoassay (IA) in patients with feminized or ambiguous genitalia. We examined two 46,XY Japanese patients with undermasculinized genitalia including hypospadias (patient 1 and patient 2). Endocrine studies by IA showed well increased serum T value after hCG stimulation (2.91 ng/mL) and a high T/A-dione ratio (4.04) in patient 1 at 2 weeks of age and sufficiently elevated basal serum T value (2.60 ng/mL) in patient 2 at 1.5 months of age. Despite such partial androgen insensitivity syndrome-like findings, whole exome sequencing identified biallelic ″pathogenic″ or ″likely pathogenic″ variants in HSD17B3 (c .188 C>T:p.(Ala63Val) and c .194 C>T:p.(Ser65Leu) in patient 1, and c.139 A>G:p.(Met47Val) and c.672 + 1 G>A in patient 2) (NM₀₀₀₁₉₇.2), and functional analysis revealed reduced HSD17B3 activities of the missense variants (∼ 43% for p.Met47Val, ∼ 14% for p.Ala63Val, and ∼ 0% for p.Ser65Leu). Thus, we investigated hCG-stimulated serum steroid metabolite profiles by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in patient 1 at 7 months of age and in patient 2 at 11 months of age as well as in five control males with idiopathic micropenis aged 1 - 8 years, and found markedly high T/A-dione ratios (12.3 in patient 1 and 5.4 in patient 2) which were, however, obviously lower than those in the control boys (25.3 - 56.1) and sufficiently increased T values comparable to those of control males. The elevated T/A-dione ratios are considered be due to the residual HSD17B3 function and the measurement by LC-MS/MS. Thus, it is recommended to establish the cut-off value for the T/A-dione ratio according to the phenotypic sex reflecting the residual function and the measurement method. Show less

Liver X receptors (LXRs) monitor endogenous sterol levels to maintain whole-body cholesterol levels and regulate inflammatory responses. Recent studies have demonstrated that LXRs may inhibit cellular proliferation, but the underlying mechanism remains unclear. Cell cycle and apoptosis regulator 2 (CCAR2), previously known as DBC1/KIAA1967, is a transcriptional regulator that regulates cellular proliferation and energy metabolism by inhibiting sirtuin 1 (SIRT1) deacetylase. Based on the findings that CCAR2 regulates several nuclear receptors, including the estrogen receptors and androgen receptor, we aimed to identify the underlying mechanism of CCAR2 regulation of LXRα. We found that CCAR2 formed a complex with LXRα in a ligand-independent manner in HepG2 cells, and in vitro pull-down assays, it revealed a direct interaction between the amino terminus of CCAR2 and the AF-2 domain of LXRα. Thereby, CCAR2 attenuates the ligand-dependent transcriptional activation function of LXRα. RNA interference-mediated depletion of endogenous CCAR2 potentiated the expression of the LXRα target genes ATP-binding cassette transporter A1 and G1, and the abrogation of CCAR2 resulted in decreased cellular proliferation. Moreover, competitive immunoprecipitation studies revealed that the LXRα downregulation involves the inhibition of SIRT1-LXRα complex formation. Therefore, these results clearly indicate a novel mechanism in which CCAR2 may regulate the transcriptional activation function of LXRα due to its specific inhibition of SIRT1 and serve to regulate cellular proliferation. Show less