This uncommon disorder is characterized by the dry, sparse and brittle hair that often break before reaching few inches. The hair appears to resemble beads on a string with the breakage points at specific internodes along the hair shaft. This condition can begin in the infancy that develops in the back of the scalp or the entire head. The exact prevalence of this disorder is not known.
Causes
Monilethrix can develop as the result of a genetic mutation in one of the several genes identified as KRT81, KRT83, KRT86 or the DSG4 gene. All these genes are involved in the production of proteins that give structure and strength to the hair strands. The KRT81, KRT83 and KRT86 are involved in the production of proteins known as keratins that are a group of fibrous proteins that form the framework of cells that make up the skin, hair and the nails. The protein produced by the DSG4 is known as desmoglein 4 which are found in structures called desmosomes which provide strength to the hair and also play the essential role of communicating signals for cells to differentiate to develop the hair shaft. The genetic mutation of any of these genes can result in the signs of this condition. Monilethrix is inherited in an autosomal recessive pattern or autosomal dominant trait. The autosomal recessive pattern of inheritance occurs when both the copies of the gene in each cell from the parents are defective. The autosomal dominant trait develops when a single copy of the altered gene in each cell is sufficient to cause this disorder.
Symptoms
Most of the infants present normal hair at birth although the condition develops during the first few months or years of their life. The hair stands are usually dry, sparse and brittle which breaks off before it can grow longer than few inches. The entire scalp may be involved or in some cases, hair shafts of other regions may also be affected such as the pubic hair, eyebrows and eyelashes. The scattered bald patches or baldness are may also occur from the progressive loss of hair. In most of the cases, the additional condition known as perifollicular hyperkeratosis can develop which is the presence of dark lesions particularly on the scalp. Affected individuals may also present abnormal nails.
Diagnosis
The diagnosis is possible with the evaluation of the hair shaft that is done with a dermatoscope to determine the breakage and constriction points. The hair samples may also be further examined with the microscope that resembles a string of evenly-spaced beads. The genetic mutation responsible for the development of the condition can also be detected to confirm the diagnosis.
Treatment
There is no cure for this condition although there have been reports of regressions among the affected cases, particularly during puberty and pregnancy. Treatment can include oral contraceptives, vitamins, retinoids and glycolic acids with limited success. As this is a life-long condition, individuals are advised to avoid exposure to sunlight and to prevent the use of hair dye or high heat. In some cases, genetic counseling may be beneficial for some of the affected individuals and their family.
References
https://rarediseases.info.nih.gov/diseases/93/monilethrix
https://rarediseases.org/rare-diseases/monilethrix/
https://ghr.nlm.nih.gov/condition/monilethrix#statistics
https://ghr.nlm.nih.gov/condition/monilethrix#statistics
