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Genetic Patterns of Hair Growth: The Genetics of Alopecia

written by: efrontiers•edited by: dianahardin•updated: 3/31/2011

Genetics can affect the patterns of human hair growth. In this article, the genetic patterns of hair growth and the occurrence of patterned hair loss, scientifically known as androgenetic alopecia, are closely evaluated.

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    Alopecia, more commonly known as hair loss, affects an estimated 35 million American men. It can be categorized into two types, namely Alopecia Areata and Androgenetic Alopecia. Alopecia areata is caused by an abnormal response of the immune system, attacking the hair follicles and causing hair to fall in patches all over the body. On the other hand, androgenetic alopecia is an inherited form of hair loss where genetics plays a huge role. This article will focus more on the latter type of hair loss, where the hair in the head thins out and the hair loss is permanent. It can affect both men and women, but 60% of the cases affect men.

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    Androgenetic Alopecia

    A more common complaint of men, androgenetic alopecia is also referred to as the male-pattern baldness in men. The hair loss creates a well-defined pattern, usually starting above both temples. With time, the hairline eventually recedes to create an M shape. Another notable pattern is the thinning of the hair near the top of the head or the crown. This progresses to partial or complete baldness.

    Although the majority of affected persons are males, androgenetic alopecia can also occur in women. It is also called female diffuse hair loss. The female pattern of hair loss is quite different in women. The hairline does not recede and only becomes thinner evenly all over the head. Total baldness is rare.

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    Hair Growth Cycle

    Hair growth begins with the follicles, a structure beneath the skin, and the life of one strand may be two to six years. After a few years, a strand will typically go through a resting phase for a few months before the hair falls out. The cycle repeats with a new hair replacing the old strand in the follicle.

    The interruption in the hair growth cycle, where hair loss occurs, is particularly due to hormones called androgens, especially the androgen called dihydrotestosterone. Androgens are essential for sexual development in males, hair growth regulation, and sex drive.

    With increased androgen levels, the hair growth cycle is shortened. Another manifestation of increased androgen levels is the thinning of the hair and slower rate of growth. When hair fall occurs, the replacement of a new strand of hair may also be delayed.

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    The Genetics Behind Androgenetic Alopecia

    According to research, the variations in only one gene have been identified to play a significant role in the occurrence of androgenetic alopecia. At the time of this writing, studies established that the gene behind the occurrence of androgenetic alopecia is the AR gene.

    The AR gene is responsible for providing instructions for the production of the protein to androgen receptors, the agents which allow the body to respond appropriately to dihydrotestosterone and other androgens. The variations in AR genes result in varying levels of activity of the androgen receptors within the hair follicles; however, studies are still determining how these genetic variations increase the risk of patterned hair loss and affect the genetic patterns of hair growth.

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    The Genetic Patterns of Androgenetic Alopecia

    The genetic patterns of hair growth, particularly concerning androgenetic alopecia, remain unclear due to several genetic and environmental factors. Patterned hair loss has the highest tendency of occurrence when there is a close relative with the same condition; the condition is known to cluster in families.

    Researchers are continuously studying the specific roles of the different variations of AR genes with the genetic patterns of hair growth. In addition, other environmental factors which may contribute to increased risks remain under investigation.

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    Although variations in the AR gene has been identified as the reason behind patterned hair loss, the specific details on how these variations affect the genetic patterns of hair growth or increase the risk of androgenetic alopecia is not yet known. Nevertheless, it is recommended that one should consult a physician and treatment providers to address the diagnosis and management of androgenetic alopecia.

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