Expansion of the genotypic and phenotypic spectrum of xeroderma pigmentosum in Chinese population

XPG: a multitasking genome caretaker

The XPG/ERCC5 endonuclease was originally identified as the causative gene for Xeroderma Pigmentosum complementation group G. Ever since its discovery, in depth biochemical, structural and cell biological studies have provided detailed mechanistic insight into its function in excising DNA damage in nucleotide excision repair, together with the ERCC1–XPF endonuclease. In recent years, it has become evident that XPG has additional important roles in genome maintenance that are independent of its function in NER, as XPG has been implicated in protecting replication forks by promoting homologous recombination as well as in resolving R-loops. Here, we provide an overview of the multitasking of XPG in genome maintenance, by describing in detail how its activity in NER is regulated and the evidence that points to important functions outside of NER. Furthermore, we present the various disease phenotypes associated with inherited XPG deficiency and discuss current ideas on how XPG deficiency leads to these different types of disease.

Cerebro-oculo-facio-skeletal syndrome caused by the homozygous pathogenic variant Gly47Arg in ERCC2

DNA damage repair is a pivotal mechanism in life. The nucleotide excision repair pathway protects the cells against DNA damage and involves XPD, an ATP dependent helicase that is part of the multisubunit protein complex TFIIH. XPD is encoded by the excision repair cross-complementation group 2 gene (ERCC2). Only three patients with cerebro-oculo-facio-skeletal syndrome (COFS), caused by mutations in ERCC2, have been published so far. This report describes a boy with the homozygous amino acid change p.Gly47Arg in XPD. He presented with profound microcephaly, psychomotor retardation, failure to thrive, cutaneous photosensitivity, a bilateral hearing deficit and optic atrophy, thrombocytopenia, and recurrent episodes of pneumonia. We report the first homozygous occurrence of the pathogenic variant Gly47Arg in the ERCC2 gene. Occurring homozygous, this variant was associated with COFS syndrome, leading to early death of the patient at the age of 21 months.

Identification of a ERCC5 c.2333T>C (L778P) Variant in Two Tunisian Siblings With Mild Xeroderma Pigmentosum Phenotype

Xeroderma pigmentosum (XP) is a rare autosomal recessive disorder due to a defect in the nucleotide excision repair (NER) DNA repair pathway, characterized by severe sunburn development of freckles, premature skin aging, and susceptibility to develop cancers at an average age of eight. XP is an example of accelerated photo-aging. It is a genetically and clinically heterogeneous disease. Eight complementation groups have been described worldwide. In Tunisia, five groups have been already identified. In this work, we investigated the genetic etiology in a family with an atypically mild XP phenotype. Two Tunisian siblings born from first-degree consanguineous parents underwent clinical examination in the dermatology department of the Charles Nicolle Hospital on the basis of acute sunburn reaction and mild neurological disorders. Blood samples were collected from two affected siblings after written informed consent. As all mutations reported in Tunisia have been excluded using Sanger sequencing, we carried out mutational analysis through a targeted panel of gene sequencing using the Agilent HaloPlex target enrichment system. Our clinical study shows, in both patients, the presence of achromic macula in sun exposed area with dermatological feature suggestive of Xeroderma pigmentosum disease. No developmental and neurological disorders were observed except mild intellectual disability. Genetic investigation shows that both patients were carriers of an homozygous T to C transition at the nucleotide position c.2333, causing the leucine to proline amino acid change at the position 778 (p.Leu778Pro) of the ERCC5 gene, and resulting in an XP-G phenotype. The same variation was previously reported at the heterozygous state in a patient cell line in Europe, for which no clinical data were available and was suggested to confer an XP/CS phenotype based on functional tests. This study contributes to further characterization of the mutation spectrum of XP in consanguineous Tunisian families and is potentially helpful for early diagnosis. It also indicates that the genotype-phenotype correlation is not always coherent for patients with mild clinical features. These data therefore suggest that targeted NGS is a highly informative diagnostic strategy, which can be used for XP molecular etiology determination.