In addition, local levels of DHT in so-called androgenic (5α-reductase-expressing) tissues are also markedly reduced, and this can have a strong impact on certain effects of testosterone. For instance, growth of body and facial hair and penile growth induced by testosterone may be inhibited by 5α-reductase inhibitors, and this could be considered undesirable in the context of, for instance, puberty induction. On the other hand, 5α-reductase inhibitors may prevent or reduce adverse androgenic side effects of testosterone like scalp hair loss, oily skin, acne, and seborrhea. In addition to the prevention of testosterone conversion into DHT, 5α-reductase inhibitors also prevent the formation of neurosteroids like 3α-androstanediol from testosterone, and this may have neuropsychiatric consequences in some men. Aromatase inhibitors
Aromatase inhibitors like anastrozole prevent the conversion of testosterone into estradiol by aromatase. As only a very small fraction of testosterone is converted into estradiol, this does not affect testosterone levels, but it can prevent estrogenic side effects like gynecomastia that can occur when testosterone is administered at relatively high dosages. However, estradiol exerts negative feedback on the hypothalamic–pituitary–gonadal axis and, for this reason, prevention of its formation can reduce this feedback and disinhibit gonadal production of testosterone, which in turn can increase levels of endogenous testosterone. Testosterone therapy is sometimes combined with an aromatase inhibitor for men with secondary hypogonadism who wish to conceive children with their partners. Cytochrome P450 inhibitors
Inhibitors and inducers of cytochrome P450 enzymes like CYP3A4 have been associated with little or no effect on circulating testosterone levels.
They produce a deficiency in the activity of the lysosomal enzyme acid sphingomyelinase, that breaks down the lipid sphingomyelin.Mutations in NPC1 or NPC2 cause Niemann–Pick disease, type C (NPC), which affects a protein used to transport lipids.Type D originally was separated from type C to delineate a group of patients with otherwise identical disorders who shared a common Nova Scotian ancestry. Patients in this group are known to share a specific mutation in the NPC1 gene, so NPC is used for both groups. Before the molecular defects were described, the terms "Niemann–Pick type I" and "Niemann–Pick type II" were proposed to separate the high- and low-sphingomyelin forms of the disease in the early 1980s.Niemann–Pick disease is inherited in an autosomal recessive pattern, which means both copies, or both alleles of the gene, must be defective to cause the disease. "Defective" means they are altered in a way that impairs their function. Most often, the parents of a child with an autosomal recessive disorder are carriers: they have one copy of the altered gene, but are not affected because the other copy produces the enzyme. If both parents are carriers, each pregnancy has a 25% chance of producing an affected child. Genetic counseling and genetic testing are recommended for families who may be carriers of the disease.