Androgenetic alopecia, commonly known as pattern baldness, is a widespread form of hair loss affecting both men and women. In men, this often begins with a receding hairline and thinning at the crown, while women typically experience diffuse thinning across the scalp. This condition affects a significant portion of the population, with roughly half of men experiencing some degree of hair loss by age 50, and a substantial number of women also affected, particularly after menopause. The primary driver behind androgenetic alopecia is largely inherited.
The Genetic Blueprint of Hair Loss
At the core of pattern baldness lies the Androgen Receptor (AR) gene, a key player in how the body responds to male hormones called androgens. This gene is located on the X chromosome, which men inherit from their mothers and women inherit one from each parent. Variations within the AR gene can lead to hair follicles becoming overly sensitive to androgens, particularly dihydrotestosterone (DHT). DHT is a potent form of testosterone, converted by an enzyme called 5-alpha reductase.
When DHT binds to these sensitive androgen receptors, it triggers follicular miniaturization. This causes hair follicles to shrink, shortening their growth phase and leading to the production of progressively finer, shorter hairs. The AR gene’s variations are consistently linked to susceptibility to androgenetic alopecia, accounting for a notable portion of its heritability in men.
Beyond the Primary Gene: A Complex Inheritance
While the AR gene plays a significant role, androgenetic alopecia is not solely determined by this single gene; it is considered a polygenic trait. This means that multiple genes, each contributing a small effect, interact to influence an individual’s susceptibility to hair loss. Research has identified numerous other genetic markers across various chromosomes that also contribute to the condition, such as genes on chromosomes 3, 7, 12, and 20.
These additional genes can affect different aspects of hair follicle biology or androgen metabolism. The combination and interaction of these various genetic predispositions determine the overall risk, the age at which hair loss might begin, and its eventual severity.
Understanding Inheritance Patterns and Risk
The genetic predispositions for pattern baldness are transmitted through generations via both X-linked and autosomal inheritance. Since the AR gene is on the X chromosome, men inherit this gene from their mothers. This contributes to the common observation that men may seem to inherit baldness from their mother’s side of the family, particularly from their maternal grandfather. However, the notion that baldness is solely inherited from the mother’s side is a misconception.
Genes located on autosomes (non-sex chromosomes) also play a role and can be inherited from either parent. Therefore, both paternal and maternal genetics contribute to an individual’s likelihood of developing androgenetic alopecia. While family history can offer clues about an individual’s potential risk, it is not a simple dominant or recessive pattern. The polygenic nature means that the presence of baldness in a family increases risk, but the specific pattern and severity can vary unpredictably even among close relatives.