Xeroderma pigmentosum is a hereditary genetic disease of a very rare autosomal recessive nature which consist of a hypersensitivity of the skin against ultraviolet radiation.
People who are affected have to avoid the sunlight, but the light of the moon does not give them any problem, they can only move freely outside at night. Therefore they are usually called children of the moon.
The cause of xeroderma pigmentosum is a deficiency of DNA repair enzymes which may be caused by several genetic mutations. In order for the disease to develop, a child must inherit the predisposition of both parents.
This is characterized by the appearance of sunburn after exposures to the sun briefly. The skin becomes variegated, dry, wrinkled and it ages prematurely. In addition, during childhood, children of the moon develop various malignant skin tumors. They also have tumors in other organs, especially in their eyes.
The diagnosis of the disease is established primarily through symptomatology. A genetic analysis allows the doctor to determine what form of xeroderma pigmentosum the patient suffers. There are eight types which are due to various genetic mutations. Symptoms vary depending on the form of the condition in question.
To date, no cure has been found for xeroderma pigmentosum. Therapeutic measures are limited to avoid to sunlight. In addition, periodic screening tests are necessary to discover and treat potential malignancies early. Although moon children often develop skin cancer before the age of 20, about two-thirds of those affected survive to age 40. However, there have been cases where patients have reached much higher ages.
Xeroderma Pigmentosum Definition: Xeroderma pigmentosum is an uncommon autosomal recessive disease that manifests itself in the skin, mucous membranes and is characterized by hypersensitivity to ultraviolet (UV) radiation. This pathology is due to a genetic defect of the DNA repair system which in healthy people continuously corrects DNA damage induced by the UV component of light on human genetic material (DNA). Due to this defect of the repair mechanism, it causes more sunburn and can develop skin cancer even during childhood. The affected children must avoid any contact with sunlight and they can go outside after sunset.
Incidince of Xeroderma Pigmentosum: In Europe and North America, disease affects approximately one in 250,000 births. This rate appears to be somewhat higher in Japan where the disease appears in one in 40,000 births. In other areas, there has also been an increase in the frequency of occurrence of cases as in North Africa (Tunisia, Algeria, Morocco, Libya and Egypt) and in the Middle East (Israel and Syria).
Xeroderma Pigmentosum Causes
The causes of xeroderma pigmentosum are found in the genes. This disease is caused by a congenital defect in the DNA repair system. DNA damage is caused by UV radiation from sunlight. UV radiation is divided according to its wavelength in:
- UVA rays, long wave (315-400 nm)
- UVB rays, medium wave (280-315 nm)
- UVC rays, short wave (100-280 nm)
UVC rays are filtered by the ozone layer of the Earth’s atmosphere. UVBs which do penetrate it and have a low depth of penetration and cause the formation of thymidine dimers in the DNA of cutaneous cells. Thymidine is a component of DNA. A thymidine dimer is a binding of two adjacent thymidines. If these remain in the DNA, the cell dies or becomes a cancer cell.
Typically, the cell has a repair system made up of enzymes that recognize dimers and remove them from DNA.
People who are suffering from xeroderma pigmentosum do not form such DNA endonucleases in sufficient quantity. It is an autosomal recessive pathology which means that it is only contracted by individuals who inherit the genetic defect of both parents. This is because there are two copies of each gene in the human genetic material- one copy comes from the mother and the other from the father. In xeroderma pigmentosum, both copies of the gene are abnormal. If defect only occurs in one of the copies, disease does not manifest, although these people can transmit the predisposition to their children.
Xeroderma pigmentosum is classified into seven groups (A-G) and one additional variant (V) depending on the different genetic bases. The different forms of the disease have effects that vary considerably. For example, subjects with a xeroderma pigmentosum group A-G contract skin cancer in most cases before the age of 20. On the other hand, people with the V do not usually suffer it until the age of 20 to 30 years.
The first symptoms of xeroderma pigmentosum are already present during childhood before beginning the school stage. After very short exposure to the sun, severe skin burns usually occur. The skin zones that receive solar radiation mainly face, hands and arms show very different alterations including variations in skin pigmentation. In addition, telangiectasias (dilatations of the smaller blood vessels are formed) occur.
As the duration of the disease increases, in addition to the benign cutaneous alterations arise malignant tumors, for example, basilomas, spinaliomas or melanomas. Malignant tumors in other organs, especially in eyes are also seen more frequently than in the normal population. Even so, about 70% of patients with xeroderma pigmentosum reach 40 years of age. However, life expectancy depends to a large extent on the genetic defect that causes the disease.
It is common for the symptoms of this pathology not to affect only the skin; These are manifested in many cases also in the eyes. Photophobia may be the first symptom of xeroderma pigmentosum which can be detected before skin alterations. Corneal inflammation often occurs (keratitis) and tumors form in the eye as both benign and malignant. 20% of those affected may have lower intelligence and increasing neurological symptoms, such as alterations in mobility, sensitivity disorders and hearing loss.
Xeroderma Pigmentosum Diagnosis
The diagnosis of xeroderma pigmentosum is established by means of symptomatology. The practitioner can check with the help of a blood or skin test the degree of recovery of DNA after exposure to sunlight. In some cases, this even allows to determine with precision the genetic defect presented by the patient.
When there are cases of xeroderma pigmentosum in the family, it is possible to perform a prenatal diagnosis. For this, fetal cells of the amniotic fluid obtained by means of a procedure known as amniocentesis are analyzed. Doctor inserts a thin cannula through the abdominal wall of the mother and takes a sample of amniotic fluid. It contains fetal cells which can be evaluated with regard to DNA repair system.
Xeroderma Pigmentosum Treatment
Current treatments do not allow cure for xeroderma pigmentosum. The only option is to protect yourself from skin cancer by avoiding sunlight. This is not only to say that those affected can not lie in the sun, but should completely avoid daylight whenever possible. If this is not feasible, the skin must be protected further by suitable clothing, UV goggles and creams with a very high sun protection factor. Patients should remain in closed spaces during the day in which the windows are equipped with sheets with special UV filters. Since most of the affected are children and they can only go outside after sunset.
In addition to measures to protect against sunlight, the treatment of xeroderma pigmentosum requires periodic examinations by the dermatologist in order to detect and remove as early as possible suspicious skin tumors. Genetic technology or gene therapy options are being investigated to treat this disease.
Xeroderma Pigmentosum Evolution: Xeroderma pigmentosum has an unfavorable prognosis, since malignant tumors frequently appear throughout its evolution. Even so, approximately 70% of patients survive to age 40. Depending on genetic defect whic causes disease, evolution and associated life expectancy vary considerably. Xeroderma pigmentosum may take a better course when it is detected early and patients must be avoided daylight adequately. It is also important for better course to screen regularly for early detection of cancer. These guidelines raise the expectation of life.
How to Prevent Xeroderma pigmentosum: Xeroderma pigmentosum can not be prevented. It is desirable that couples who wish to have children and be carriers of this genetic alteration should seek advice from their gynecologist.