Xeroderma pigmentosum
Types of XP
There are 8 different genetic types of Xeroderma Pigmentosum depending on the affected gene: XPA, XPB (or ERCC3), XPC, XPD (or ERCC2), XPE (or DDB2), XPF (or ERCC4), XPG (ERCC5) and XPV (or POLH)10, each one of them affecting different mechanisms of DNA repair (making them more severe or not) in the protection of the aggressions caused by UV light.
|
XP type |
Affected gene / locus |
Clinical features |
|
XP-A |
XPA / 9q22.3 |
It represents 25% of the patients with XP. Patients present a diverse range of symptoms, including the development of numerous skin cancers at an early age and serious neurological abnormalities. |
|
XP-B |
XPB (ERCC3) / 2q21 |
It is the least frequent of the XP types. It presents increased sensitivity to UV light. Patients may develop numerous skin cancers at an early age, some mild neurological abnormalities and they can present characteristics of Cockayne syndrome. |
|
XP-C |
XPC / 3p25 |
It represents 25% of the patients with XP. It is considered the classical form of XP, the most frequent form in the Caucasian population. It is the disease variant with the highest capability to repair DNA even it shows increased sensitivity to UV exposure. Patients may develop severely atypical and dense lentigines at exposed areas as well as ocular anomalies but no neurological abnormalities. |
|
XP-D |
XPD (ERCC2) / 19q13.2-q13.3 |
It represents 15% of the patients with XP. It presents increased sensitivity to UV light. Patients with this variant may develop numerous skin cancers at an early age. About neurological defects, they may present in some cases severe neurological defects with progressive degeneration such as sensorineural deafness, ataxia and mental retardation. |
|
XP-E |
XPE (DDB2) / 11p11-p12 ; 11q12-q13 |
Low frequency. A less aggressive form of XP, it is limited to skin problems. Patients present the development of cutaneous cancers at a later age and they do not present neurological symptoms. |
|
XP-F |
XPF (ERCC4) / 16p13.3 |
Low frequency. A less aggressive form of XP, most of the cases in the Japanese population. It presents the development of cutaneous cancers at a later age and it does not present neurological nor ocular symptoms. |
|
XP-G |
XPG (ERCC5) / 13q32-q33 |
Low frequency but aggressive. Increased sensitivity to UV light. Development of numerous skin cancers at an early age and it presents neurological abnormalities in some cases. |
|
XP-variant |
XPV (POLH) / 6p21.1 |
It represents 20% of the patients and it is very similar to XP-C. Increased sensitivity to UV exposure but less photosensitivity than other forms of XP. Higher risk of cutaneous cancers development after 30 years old and it does not present neurological symptoms nor ocular problems. |