Androgenetic alopecia, commonly known as male or female pattern baldness, is a widespread condition characterized by progressive hair loss. This type of hair loss is primarily influenced by an individual’s genetic makeup, stemming from a combination of inherited genetic factors that interact with hormonal influences rather than a single “baldness gene.”
The Key Genetic Contributor
The most significant genetic factor identified in pattern baldness is the Androgen Receptor (AR) gene, located on the X chromosome. This gene provides instructions for creating androgen receptors, proteins found in hair follicles that respond to hormones called androgens. One crucial androgen is dihydrotestosterone (DHT), a testosterone derivative.
Variations within the AR gene can lead to androgen receptors that are more sensitive to androgens like DHT. When these highly sensitive receptors bind with DHT, they trigger follicular miniaturization, where hair follicles progressively shrink and produce finer, shorter, and eventually non-pigmented hairs. This increased sensitivity to DHT is a primary driver of hair thinning and loss in individuals predisposed to androgenetic alopecia. The AR gene is considered the strongest genetic predictor for this type of hair loss.
Additional Genetic Factors
While the AR gene plays a major role, pattern baldness is a polygenic condition. Many other genetic variations influence the likelihood and progression of hair loss. These additional genes often have a less significant individual impact compared to the AR gene but collectively contribute to the overall genetic predisposition.
For instance, variations on chromosome 20 have been linked to hair loss, some involving genes like 20p11, associated with prostaglandin D2 (PGD2) production, a molecule that can inhibit hair growth. Other genes, such as FOXC1, EDA2R, WNT10A, HEPH, CEPT1, and EIF3F, are also implicated, influencing processes like hair follicle development or the hair growth cycle. The interplay between these various genes determines an individual’s unique susceptibility and the specific pattern of their hair loss.
Inheritance Patterns and Family Links
The inheritance of pattern baldness involves a complex interplay of genetic factors, which can lead to misconceptions about its transmission. The AR gene, being on the X chromosome, exhibits an X-linked inheritance pattern. Males inherit their single X chromosome from their mother, meaning a mother can pass on an AR gene variant to her son, making her family history a significant indicator for male pattern baldness.
However, baldness is not solely inherited from the mother’s side; other contributing genes are located on autosomes and can be inherited from either parent. This polygenic nature means both maternal and paternal family histories can influence an individual’s risk. While a family history of pattern baldness increases an individual’s risk, it is not a definitive predictor due to the complex interaction of multiple genes and varying degrees of penetrance.