Monilethrix is a rare inherited disorder characterized by sparse, dry, and/or brittle hair that often breaks before reaching more than a few inches in length. The hair may lack luster, and there may be patchy areas of hair loss (alopecia). Another common symptom may be the appearance of elevated spots (papules) surrounding the hair follicles that may be covered with gray or brown crusts or scales (perifollicular hyperkeratosis). When viewed under a microscope, the hair shaft resembles a string of evenly-spaced beads. In most cases, monilethrix is inherited as an autosomal dominant trait.
In most cases of monilethrix, the hair is normal at birth; it may then be slowly replaced by abnormal hair during the first few months to two years of life. In some rare cases, the hair may be abnormal at birth (congenital). The hair may be sparse, dry, lusterless, and/or brittle. In addition, the hair is unusually short and breaks off before growing longer than a few inches.
Scalp hair is most frequently affected by monilethrix. The entire scalp or small areas of the scalp may be involved. In some cases, the eyelashes, eyebrows, pubic hair, and/or other body hair may also be affected. In addition, the patchy loss of hair (alopecia) is a common characteristic of this disorder. Progressive hair loss may lead to scattered bald patches or baldness.
In most cases of monilethrix, a skin condition known as perifollicular hyperkeratosis may develop. The condition is characterized by firm dark lesions (papules) covered with gray-brown scales and crusts that appear on the skin, especially the scalp.
The severity and progression of symptoms may vary greatly from case to case. In some cases, individuals with monilethrix may experience remission of the disorder for no apparent reason (spontaneously), most often during puberty or pregnancy. In other cases, the condition may remain the same throughout life or the symptoms may become progressively worse.
In most cases, monilethrix is inherited as an autosomal genetic trait. Genetic diseases are determined by two genes, one received from the father and one from the mother.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.
Some cases of monilethrix result from defects (mutations) in the hair cortex keratin gene(s) (HB1; KRTHB1 and HB6; KRTHB6) located on the long arm (q) of chromosome 12 (12q13). Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Pairs of human chromosomes are numbered from 1 through 22, and an additional 23rd pair of sex chromosomes which include one X and one Y chromosome in males and two X chromosomes in females. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 12p13” refers to band 13 on the long arm of chromosome 12. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
The physical findings associated with monilethrix may result from abnormalities of the hard keratin of hair and nails.
Monilethrix affects males and females in equal numbers. The exact number of people affected by this disorder is not known. Monilethrix may be apparent at birth or by the age of two years. In some cases, the symptoms may improve at puberty or during pregnancy; in other cases, the symptoms may remain the same throughout life.
The diagnosis of monilethrix may be confirmed by a thorough clinical evaluation and microscopic examination of the hair. When viewed under a microscope, the hair resembles a string of evenly-spaced beads.
No specific treatment exists for monilethrix. Spontaneous resolution following puberty has occurred in some cases. In affected females, the condition improves during pregnancy. Genetic counseling will be of benefit for affected individuals and their families. Other treatment is symptomatic and supportive.
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