Male hypogonadism as a candidate of deficiency of postnatal testicular growth or differentiating factor(s): a new autosomal recessive mutation in the rat

A new rat mutant showing severe male hypogonadism (hgn for the gene symbol) was found and isolated from the hereditary hydronephrosis rat strain originating from the Wistar-Imamichi rat. The affected rats have very tiny testes that weigh 26 mg in the adult, and contain small numbers of seminiferous tubules with degenerated Sertoli cells. It is difficult to identify the gonocyte in the seminiferous tubules in the mutant testis. Very small male accessory sex organs are all present in the mutant. The number of chromosomes is 42 (40A + XY). The structure of each chromosome is normal, showing that the mutant has male sex genes. Thus, it was considered that this status is not due to either lack of the H-Y antigen or Muellerian inhibiting factor or expression of the Tfm. By analyzing the pedigree of the matings producing the mutant, it was concluded that the status was expressed only in the male, but inherited with a single autosomal recessive trait with existence of the phenotypically normal fertile female recessive homozygote. A possible deficiency of certain known or unknown testicular growth or differentiating factor(s) in the mutant is suggested.