Androgenetic alopecia is a common form of hair loss in both men and women. In men, it is also known as male pattern baldness, and in women, it is also known as female pattern hair loss.

In men, hair is lost in a well-defined pattern, beginning above both temples. Over time, the hairline moves back (recedes) to form a characteristic "M" shape. Hair also thins at the top of the head (vertex or crown), often progressing to partial or complete baldness.

The pattern of hair loss in women differs from male-pattern baldness. In women, the hair becomes thinner at the top of the head, and the middle part widens. The hairline does not typically recede. Androgenetic alopecia in women rarely leads to total baldness.

Androgenetic alopecia in men has been associated with several other medical conditions, including coronary heart disease and enlargement of the prostate. Additionally, prostate cancer, disorders of insulin resistance (such as diabetes and obesity), and high blood pressure (hypertension) have been related to androgenetic alopecia.

In women, this form of hair loss is associated with an increased risk of polycystic ovary syndrome (PCOS). PCOS is characterized by a hormonal imbalance that can lead to irregular menstruation, acne, excess hair elsewhere on the body (hirsutism), and weight gain.

Androgenetic alopecia affects an estimated 50 million men and 30 million women in the United States. Androgenetic alopecia can start as early as a person's teens, and the risk increases with age; more than 50 percent of men over age 50 have some degree of hair loss. In women, hair loss is most likely after menopause.

A variety of genetic and environmental factors likely play a role in causing androgenetic alopecia. Although researchers are studying risk factors that may contribute to this condition, most of these factors remain unknown. Researchers have determined that this form of hair loss, particularly in men, is related to hormones called androgens, specifically an androgen called dihydrotestosterone (DHT). Androgens play a role in female pattern hair loss, but other factors that are not yet known are also involved.

Androgens are important for normal male sexual development before birth and during puberty. Androgens also have other important functions in both males and females, such as regulating hair growth and sex drive.

Hair growth begins under the skin in structures called follicles. Each strand of hair normally grows for 2 to 6 years, goes into a resting phase for several months, and then falls out. The cycle starts over when the follicle begins growing a new hair.

Androgens help control this cycle. However, too much stimulation of hair follicles by androgens may lead to a shorter growth period, resulting in shorter and thinner strands of hair. The growth of new hair to replace strands that are shed is also delayed. Together, these changes lead to hair thinning or loss.

Researchers suspect that variants (also called mutations) in several genes play a role in androgenetic alopecia. However, scientific studies have confirmed only that variations in one gene, the AR gene, are involved in this condition. The AR gene provides instructions for making a protein called an androgen receptor. Androgen receptors allow the body to respond appropriately to DHT and other androgens. Studies suggest that variations in the AR gene result in androgen receptors that are more easily stimulated by androgens than normal, leading to increased activity of the receptors in hair follicles. It remains unclear, however, how these genetic changes increase the risk of hair loss in men and women with androgenetic alopecia.

Researchers continue to investigate the connection between androgenetic alopecia and other medical conditions, such as coronary heart disease and prostate cancer in men and polycystic ovary syndrome in women. They believe that some of these disorders may be associated with elevated androgen levels, which may help explain why they tend to occur with androgen-related hair loss.

Normal Function

The AR gene provides instructions for making a protein called an androgen receptor. Androgens are hormones (such as testosterone) that are important for normal male sexual development before birth and during puberty. Androgen receptors allow the body to respond appropriately to these hormones.

The receptors are present in many of the body's tissues, where they attach (bind) to androgens. The resulting androgen-receptor complex then binds to DNA and regulates the activity of androgen-responsive genes. By turning the genes on or off as necessary, the androgen receptor helps direct the development of male sexual characteristics. Androgens and androgen receptors also have other important functions in both males and females, such as regulating hair growth and sex drive.

In one region of the AR gene, a DNA segment known as CAG is repeated multiple times. This CAG segment is called a triplet or trinucleotide repeat. In most people, the number of CAG repeats in the AR gene ranges from fewer than 10 to about 36.

Health Conditions Related to Genetic Changes

Androgen insensitivity syndrome

Hundreds of different variants (also called mutations) in the AR gene have been identified in people with androgen insensitivity syndrome, a condition that affects sexual development before birth and during puberty. Most of these variants are changes in single DNA building blocks (base pairs). Other variants insert or delete multiple base pairs in the gene or affect how the gene is processed into a protein. Some variants lead to an abnormally short version of the androgen receptor protein, while others result in the production of an abnormal receptor that cannot bind to androgens or to DNA.

As a result of these changes, cells that are normally sensitive to androgens become less responsive to these hormones or unable to use these hormones at all. People with this condition are genetically male, with one X chromosome and one Y chromosome in each cell. Because their bodies are unable to respond to androgens, they may have mostly female sex characteristics or signs of both male and female sexual development.

Variants that eliminate the function of the androgen receptor cause complete androgen insensitivity syndrome. Genetic changes that significantly reduce but do not eliminate the receptor's activity cause partial androgen insensitivity syndrome. Variants that only slightly reduce the activity of the receptor cause mild androgen insensitivity syndrome.

Spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy, a disorder of specialized nerve cells that control muscle movement (motor neurons), results from an expansion of the CAG trinucleotide repeat in the AR gene. Instead of the typical 10 to 36 repeats, CAG is repeated from 38 to more than 60 times in people with this disorder. Although the extended CAG region changes the structure of the androgen receptor, it is unclear how the altered protein damages nerve cells. Researchers believe that a fragment of the androgen receptor protein containing the CAG repeats accumulates within these cells and interferes with normal cell functions. This buildup leads to the gradual loss of motor neurons, which results in muscle weakness and wasting (atrophy).

Androgenetic alopecia

Changes in the AR gene are associated with an increased risk of androgenetic alopecia, a form of hair loss also known as male pattern baldness in men and female pattern hair loss in women. The variations change the number or order of DNA building blocks (base pairs) that make up the AR gene. These genetic changes appear to be most frequent in men with hair loss that begins at an early age. Researchers believe that AR gene variations may increase the activity of androgen receptors in the scalp. Although androgenetic alopecia is related to the effects of androgens on hair growth, it remains unclear how changes in the AR gene increase the risk of hair loss in people with this condition.

Polycystic ovary syndrome

MedlinePlus Genetics provides information about Polycystic ovary syndrome

Prostate cancer

MedlinePlus Genetics provides information about Prostate cancer

Other Names for This Gene

• AIS
• ANDR_HUMAN
• androgen receptor (dihydrotestosterone receptor; testicular feminization; spinal and bulbar muscular atrophy; Kennedy disease)
• DHTR
• HUMARA
• KD
• NR3C4
• SBMA
• SMAX1
• TFM

Genomic Location

The inheritance pattern of androgenetic alopecia is unclear, because many genetic and environmental factors are likely to be involved. This condition tends to cluster in families, however, and having a close relative with patterned hair loss appears to be a risk factor for developing the condition.

Only 2 drugs currently have US Food and Drug Administration (FDA) approved indications for treatment of androgenetic alopecia:

• Minoxidil: Appears to lengthen the duration of the anagen phase (the active growth phase of hair follicles), and it may increase the blood supply to the follicle. Regrowth is better at the top of the head than in the front areas and is not noted for at least 4 months. It is used as a 2% or a 5% solution that rubs into the scalp and the 5% solution may work better. However, if the treatment is stopped the baldness returns. It works better in patients who just starting having the alopecia and who have small areas of hair loss.
• Finasteride: It can only be used in men and is better for balding at the top of the head. If the treatment is stopped the baldness returns. It cannot be used in women who are still able to have children because it can result in ambiguous genitalia in male babies and it does not seem to be effective in women. The doses are about 1 mg daily by mouth.

Minoxidil use for several months can result in an eye condition known as central chorioretinopathy (an eye disease that lead to temporary visual impairment) , which can go back to normal after 1 months of not using the drug. Finasteride has no known side effects in men, according to several studies, but it cannot be used in women who are still trying to have children because it may produce fetal genital malformations.

Every patient is unique and only the doctor can evaluate and determine the best treatment.

Some drugs that are not approved by the FDA but may be helpful are:

• Spironalactone: In women with androgenetic alopecia.
• Oral contraceptives: In women.
• Dutasteride: Is currently in study.
• Topical latanoprost 0.1% is currently used to treat glaucoma and using it results in an increase of eyelashes. Some studies have shown that this medication could be useful for stimulating hair follicle activity and treating hair loss.
• Follistatin, a human cell derived medication is also in study.

Also, low-level laser light therapy, a red light hairbrush–like device has shown some good results.

Surgical treatment of androgenetic alopecia has good cosmetic results. The main problem is covering the bald area with donor plugs (or follicles) sufficient in number to be effective. Micrografting produces a more natural appearance than the old technique of transplanting plugs.

It is important for the patients with androgenetic alopecia to be evaluated for treatable causes of “telogen effluvium” (diffuse hair shedding, often starting suddenly) like anemia or hypothyroidism, especially in patients who had a rapid progress of their disease or a sudden start of the disease. The following treatment options are recommended for women by some experts:

• Spironolactone and cyproterone acetate
• Finasteride
• Minoxidil.

These treatments are most effective when started early.