Male Pattern Baldness Inheritance
Male pattern baldness (androgenetic alopecia) is inherited primarily from the maternal side of the family, with the X-chromosomal androgen receptor gene being the major genetic determinant. The maternal grandfather's hair pattern is often more predictive than the father's pattern 1.
Genetic Basis
The androgen receptor (AR) gene located on the X chromosome is the cardinal prerequisite for early-onset androgenetic alopecia, with an etiological fraction of 0.46 1. Since males inherit their single X chromosome from their mother, this explains the strong maternal inheritance pattern.
- The X-chromosomal location of the AR gene emphasizes the importance of the maternal lineage in inheritance 1
- A polyglycine-encoding GGN repeat in exon 1 of the AR gene is a plausible functional variant conferring susceptibility 1
- Males only need one copy of the susceptibility variant (from mother) to express the phenotype, while females would need variants on both X chromosomes 1
Inheritance Pattern Complexity
The inheritance is polygenic rather than following simple Mendelian patterns, meaning multiple genes contribute to the condition 2, 3.
- No clear single-gene inheritance pattern has been observed in population studies 2
- The relatively strong concordance between fathers and sons is not consistent with simple autosomal dominant inheritance 2
- Genetic predisposition is multifactorial and susceptible to epigenetic and environmental factors 3
- Studies of the 5-alpha-reductase genes (SRD5A1 and SRD5A2) found no significant association with male pattern baldness, ruling out these as major determinants 2
Clinical Implications
When assessing family history for androgenetic alopecia risk, focus on the maternal grandfather and maternal uncles rather than solely on the father's pattern 1.
- The condition is androgen-dependent, requiring both genetic predisposition and adequate androgen levels 4, 3
- Dihydrotestosterone (DHT) drives the phenotypic changes through follicle miniaturization 3
- Androgenetic alopecia has been associated with increased risk of ischemic heart disease, hypertension, and metabolic syndrome 5