A locus responsible for hypogonadism (hgn) is located on rat Chromosome 10

Hypogonadic rats of the HGN inbred strain show male sterility controlled by an autosomal single recessive allele (hgn). The testis weight of adult hgn/hgn rats is about 1% that of normal rats, and only a few thin seminiferous tubules surrounded by islet-like conformations of Leydig cells are present in the fibrous interstitial tissue of the testis (Suzuki et al. 1988). Primordial germ cells do exist in the neonatal hgn/hgn testis, but cannot differentiate into spermatogonia and degenerate before entering meiosis (Suzuki et al, 1998). hgn/hgn females have reduced fertility, including a small litter size, a reduced number of oocytes, and early reproductive senescence (Suzuki et al. 1992). hgn/hgn rats of both sexes also show bilateral hypoplastic kidney (HPK) with a reduced number (only one-quarter) of glomeruli (Suzuki et al. 1991; Suzuki and Suzuki 1995). Whether the phenotypes of hypogonadism and HPK are caused by a mutation in a single gene or defects in different genes located close to each other remains unclear. No other mutant animal or human disease showing a phenotype similar to that of the hgn/hgn rat has been reported. The hgn/hgn rat would, therefore, be a useful model for investigating the development of mammalian reproductive and urinary organs. In this study, linkage analysis was performed to determine the chromosome location of the hgn locus and to obtain information about candidate genes for hgn.