see also:

• androgens
• alopecia
• polycystic ovary syndrome (PCOS) / polyendocrine metabolic ovarian syndrome (PMOS)

• androgenetic alopecia is male pattern balding which appears to have a multi-factorial causation although genetic polymorphisms appear to have a key role which may influence the hair follicle cycle and the drivers of this cycle such as androgens, and insulin-like growth factors (IGFs)
• 30% of men developed androgenetic alopecia by the age of 30 and 50% by the age of 50
• the three key features of androgenetic alopecia pathogenesis are:
  • alteration of hair cycle dynamics
  • follicular miniaturisation
  • inflammation
• eunuchs, patients with androgen-insensitivity syndrome and those with 5α-reductase deficiency do NOT go bald in this manner, suggests that androgenetic alopecia is induced by activation of follicular androgen receptors by dihydrotestosterone.
• there are possible associations with other conditions such as:
  • polycystic ovary syndrome (PCOS) / polyendocrine metabolic ovarian syndrome (PMOS) in daughters perhaps via IGF-2 polymorphism
  • metabolic syndrome and ischaemic heart disease (IHD)
    • risk of androgenetic alopecia is higher in those with higher BMI at age 21yrs
    • increased risk of ischaemic heart disease (IHD) seems mainly in those with early onset baldness
  • colonic neoplasms
  • prostate cancer - 50% increased risk with vertex pattern, but no increase risk with frontal pattern, although all forms showed an increased risk of high grade cancers in men aged 60-69yrs ¹⁾

• this form of alopecia clearly has a familial association and is more common in some ethnic groups
• the androgen receptor gene Stu1 restriction fragment length polymorphism on the X chromosome appears to be necessary (as it is present in 98% of young bald men and 92% of older bald men) but of itself is not sufficient to cause the condition (it occurs in 77% of non-bald men)²⁾
• other candidate genes include³⁾:
  • SRDA1 and SRDA5 coding for the two variants of the 5a-reductase enzymes
  • insulin gene
  • the aromatase gene
  • gene for the Erα oestrogen receptor
  • the non-recombinant area of the Y chromosome
  • IGF-2 gene
    • a polymorphism of this confers a high risk of polycystic ovary syndrome (PCOS) / polyendocrine metabolic ovarian syndrome (PMOS) which may be related
    • while this gene is autosomal, the maternal allele is de-activated due to genomic imprinting

• oral inhibitors of 5α-reductase arrest progression of androgenetic alopecia in over 90% of men and partially reverse it in over 65%