Xeroderma pigmentosum – Fakten und Perspektiven

Genetic Disorders with Predisposition to Paediatric Haematopoietic Malignancies—A Review

The view of paediatric cancer as a genetic disease arises as genetic research develops. Germline mutations in cancer predisposition genes have been identified in about 10% of children. Paediatric cancers are characterized by heterogeneity in the types of genetic alterations that drive tumourigenesis. Interactions between germline and somatic mutations are a key determinant of cancer development. In 40% of patients, the family history does not predict the presence of inherited cancer predisposition syndromes and many cases go undetected. Paediatricians should be aware of specific symptoms, which highlight the need of evaluation for cancer syndromes. The quickest possible identification of such syndromes is of key importance, due to the possibility of early detection of neoplasms, followed by presymptomatic genetic testing of relatives, implementation of appropriate clinical procedures (e.g., avoiding radiotherapy), prophylactic surgical resection of organs at risk, or searching for donors of hematopoietic stem cells. Targetable driver mutations and corresponding signalling pathways provide a novel precision medicine strategy.Therefore, there is a need for multi-disciplinary cooperation between a paediatrician, an oncologist, a geneticist, and a psychologist during the surveillance of families with an increased cancer risk. This review aimed to emphasize the role of cancer-predisposition gene diagnostics in the genetic surveillance and medical care in paediatric oncology.

Xeroderma Pigmentosum: Gene Variants and Splice Variants

The nucleotide excision repair (NER) is essential for the repair of ultraviolet (UV)-induced DNA damage, such as cyclobutane pyrimidine dimers (CPDs) and 6,4-pyrimidine-pyrimidone dimers (6,4-PPs). Alterations in genes of the NER can lead to DNA damage repair disorders such as Xeroderma pigmentosum (XP). XP is a rare autosomal recessive genetic disorder associated with UV-sensitivity and early onset of skin cancer. Recently, extensive research has been conducted on the functional relevance of splice variants and their relation to cancer. Here, we focus on the functional relevance of alternative splice variants of XP genes.

Genetisch bedingte Hauterkrankungen – Xeroderma pigmentosum und das CEDNIK-Syndrom

Die Rostocker Hautklinik ist Europäisches Referenznetzwerkzentrum für seltene Hauterkrankungen mit den besonderen Schwerpunkten Xeroderma pigmentosum und Ichthyosen. Diese Themen vertreten wir auch in der medizinischen Grundlagenforschung.

Xeroderma pigmentosum (XP) ist eine seltene, autosomal-rezessive Erkrankung, die entsprechend der Gendefekte in 7 Komplementationsgruppen – XP-A bis XP-G sowie die sog. XP-Variante (XP-V) – eingeteilt wird. XP ist ein Nukleotid-Exzisions-Reparatur-Defektsyndrom und äußert sich v. a. durch vorzeitige Hautalterung und frühzeitige Entwicklung von Hauttumoren.

Das seltene, neurokutane CEDNIK-Syndrom ist eine autosomal-rezessive Erkrankung, der eine Loss-of-Function-Mutation in SNAP29 zugrunde liegt. SNAP29 ist ein SNARE-Protein und an intrazellulären Membranfusionen beteiligt. CEDNIK ist ein Akronym für den mit dem Syndrom assoziierten Symptomkomplex aus zerebraler Dysgenese, Neuropathie, Ichthyose und Palmoplantarkeratosen. CEDNIK-Patienten weisen neben der Ichthyose zudem Gedeihstörungen, eine psychomotorische Retardierung und faziale Dysmorphien auf.

Sunlight, Vitamin D, and Xeroderma Pigmentosum

Sunlight, in particular UV-B radiation, is an important factor for endogenous vitamin D production as 80-90% of the required vitamin D needs to be photosynthesized in the skin. The active form of vitamin D, vitamin D₃ or calcitriol, binds to the ligand-activated transcription factor vitamin D receptor (VDR) for genomic and non-genomic effects. Recently, calcitriol and analogs have been shown to have antiproliferative effects in mouse and human BCC and SCC cell lines in vitro. As UV radiation plays a critical role in the photosynthesis of vitamin D, stringent sun protection, as recommended for xeroderma pigmentosum (XP) patients, may impact their vitamin D levels.XP is a rare autosomal recessive disorder with a worldwide prevalence of 1 in 1,000,000. XP can be divided into seven different complementation groups: XP-A to XP-G. The complementation groups correspond with the underlying gene defect. Defects in these genes lead to a defective nucleotide excision repair (NER), which is necessary to remove UV-induced DNA damage such as the UV photoproducts cyclobutane pyrimidine dimers (CPD) and 6-4 pyrimidine-pyrimidone (6-4 PP) dimer. Additionally, a variant form with a mutation in the translational polymerase η gene (PolH), also called XP variant (XPV), exists. Patients with XPV show a defect in translesion synthesis. Due to their inability to repair UV-induced lesions, XP patients exhibit an increased risk for UV-induced nonmelanoma skin cancer (NMSC) such as basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) as well as melanoma. Although no curative therapy for XP exists today, numerous options for the treatment and prophylaxis of skin cancer have become available.