A 30-year-old man consults a gynecologist for the cause of his infeility. On questioning, he informs the doctor that he never suffered from any major illness in the past and also got married 5 years back. However, his physical examination reveals failure of testes to descend down in the scrotum. The semen analysis shows absence of spermatozoa. The blood lab repo shows plasma gonadotrophins, 12 Ru/24 hrs; Plasma testosterone, 7 ug/l and semen 2 ml. The factor responsible for the absence of spermatozoa in this patient is?