Self-Checks
The first step in getting diagnosed may be in noticing signs of extreme sun sensitivity in someone. After a day at the beach, even with sunscreen, you may find yourself with a burn from time to time. XP is more serious than this. Look for the following:
Signs of blistering and burning after a very short time in the sun or even inside under fluorescent lights, beginning as early as infancy (An early clue might be a severe sunburn after the first time a child is in the sun. )Freckling on the face and body in a young child, and pigmentation changes (lighter or darker)Experiencing eye issues with light sensitivityConcerns about neurological and developmental issues such as a smaller-than-normal head size, progressive deafness, or progressive intellectual impairment
Physical Examination
Diagnosing this rare disorder usually begins with the healthcare professional getting a complete family history and consulting with the patient, going over the signs that are concerning.
While family history may be important, keep in mind that not having other relatives with this condition is not enough to rule XP out. Many people with XP have no family history of it.
Besides considering the patient’s clinical symptoms, the doctor will also conduct an examination. This may mean looking for any signs of recent burns or freckling. However, these signs could mean the person has sun sensitivity due to other causes, so they alone are not enough to make this kind of diagnosis.
Labs and Tests
A DNA repair test may be needed if there is a strong suspicion of xeroderma pigmentosum. This looks for changes to a DNA sample after it has been exposed to ultraviolet (UV) light. It especially checks for changes in newly-made DNA strands.
To perform this test, a clinician will likely take a small skin sample from an area of the body unexposed to the sun, such as from the buttocks or the upper inner arm.
If there is reason to suspect that a fetus may have XP due to a family history of the condition, it is also possible to make a prenatal diagnosis. Amniocentesis, in which a needle is inserted into the sac surrounding the fetus, can obtain a sample of amniotic fluid for a DNA repair test.
Molecular genetic testing can also find mutations in the genes responsible for producing XP.
Imaging
XP can have some neurological effects that impact about 25% of patients. Such neurological issues can arise due to loss of brain-related nerve cells.
Some neurological symptoms that may be noticed include:
Smaller head size Progressive cognitive impairment High-frequency hearing loss Seizures Muscle tightness Poor muscle control
Doctors may use imaging scans such as magnetic resonance imaging (MRI) and computed tomography (CT) to check the brain for signs of shrinkage in patients. It is thought that this shrinkage is linked to an accumulation of unrepaired DNA damage in brain cells, but this has not yet been verified.
Differential Diagnosis
The doctor will consider other conditions that could exhibit some of the signs and symptoms with which the patient is presenting. Instead of first occurring at a very young age, pigmentation changes (freckles and lighter or darker coloration) may not first appear until adolescence or beyond for some cases of XP.
This means that other potential causes for skin issues must first be ruled out, including the following:
Solar urticaria: This rare allergy to sunlight may mimic XP. However, if skin symptoms linger, solar urticaria can be ruled out since this usually resolves within an hour or so of being indoors. Erythropoietic protoporphyria: This is a rare metabolic disorder in which there is redness, swelling, burning, and itching of the skin after sun exposure. With erythropoietic protoporphyria, not all exposed skin is affected. Testing for porphyrins (proteins that help make hemoglobin, an iron-rich protein in red blood cells) can rule this out if the test is normal. Cockayne syndrome: People with this rare inherited form of dwarfism can have abnormal sensitivity to light. However, it does not produce the same pigmented changes usually found in XP. It is usually associated with severe intellectual impairment, as well as dwarfism. Rothmund-Thompson syndrome: This syndrome can include a sun-sensitive rash, but it is unlike XP in that patients do not have pigmentation changes. Carney complex and Leopard syndrome: These also involve pigmented lesions, but the lesions are not related to sun exposure. Peutz-Jeghers syndrome: With this syndrome, people develop dark-colored spots and have a heightened risk of certain cancers. However, skin issues tend to be around the mouth or on the hands and feet. Also, this is an autosomal dominant condition, meaning it is passed down from one parent. Taking a family history should exclude this as a cause.
Summary
Getting a diagnosis for someone with XP can involve taking a history around symptoms of sun sensitivity, as well as of any family connection. Also, a physical examination of the skin looking for pigment issues such as freckling will be done. Genetic testing and DNA repair testing may also be done.
A Word From Verywell
If you are concerned that your sun sensitivity may be linked to XP, consult a physician. Having some sun sensitivity does not necessarily mean that XP is the cause, but it may bring you relief to learn what the reason is for your sun sensitivity. Only with a thorough history and workup can you tell if XP is the source of your symptoms.
