A novel mutation of CYLD in a Chinese family with multiple familial trichoepithelioma

Genetic Testing in CYLD Cutaneous Syndrome: An Update

CYLD cutaneous syndrome (CCS) is an inclusive label for the inherited skin adnexal tumour syndromes Brooke–Spiegler Syndrome (BSS-OMIM 605041), familial cylindromatosis (FC – OMIM 132700) and multiple familial trichoepitheliomas (MFT-OMIM 601606). All three syndromes arise due to germline pathogenic variants in CYLD, a tumour suppressor gene (OMIM 605018). CCS is transmitted in an autosomal dominant pattern, and has variable expressivity, both of the three syndromic phenotypes, and of the severity of tumour burden. Age-related penetrance figures are not precisely reported. The first tumours typically appear during puberty and progressively accumulate through adulthood. Penetrance is typically high, with equal numbers of males and females affected. Genetic testing is important for confirmation of the clinical diagnosis, genetic counselling and family planning, including preimplantation diagnosis. Additionally, identified CCS patients may be eligible for future clinical trials of non-surgical pre-emptive interventions that aim to prevent tumour growth. In this update, we review the clinical presentations of germline and mosaic CCS. An overview of the germline pathogenic variant spectrum of patients with CCS reveals more than 100 single nucleotide variants and small insertions and deletions in coding exons, most frequently resulting in predicted truncation. In addition, a minority of patients have large deletions involving the CYLD gene, intronic pathogenic variants that affect splicing, or inversions. We discuss germline and somatic testing approaches. Somatic testing of tumour tissue, relevant in mosaic CCS, can reveal recurrently detected pathogenic variants when two or more tumours are tested. This can influence genetic testing of children, who may inherit this as a germline variant, and inform genetic counselling and prenatal diagnosis. Finally, we discuss testing technologies that are currently used, their benefits and limitations, and future directions for genetic testing in CCS.

Marie Unna hereditary hypotrichosis accompanied by multiple familial trichoepithelioma in a Chinese family

Marie Unna hereditary hypotrichosis (MUHH) and multiple familial trichoepithelioma (MFT) are both autosomal dominant disorders. Recently, certain genes (HR and EPS8L3) have been found to be responsible for MUHH, while CYLD has been demonstrated to be the main pathogenic gene in MFT patients. However, there exist a number of CYLD mutation-negative MFT cases, for which the causative gene has been unknown. Here, we identified a large, five-generation Han Chinese family with several patients presenting with MUHH and MFT. Sanger sequencing of three genes in 13 family members was performed. We found that the c.1A>G mutation in an inhibitory upstream open-reading frame of HR (U2HR) was present in all MUHH patients, while no pathogenic variants were found in the 3'- or 5'-untranslated regions, exons or flanking intronic sequences of EPS8L3 or CYLD in any family members. Subsequently, whole-genome sequencing was performed for five affected and one unaffected family member. We found no CYLD variants but identified an FABP12 variant (rs536105592 G>A) in the patients with both MUHH and MFT. These results suggest that the U2HR mutation was responsible for MUHH and the FABP12 variant may be coincidental in the accompanying MFT in this unique pedigree. This report deepens our understanding of the genetic basis of hair follicle diseases.

The cylindromatosis (CYLD) gene and head and neck tumorigenesis

Germline CYLD mutation is associated with the development of a rare inheritable syndrome, called the CYLD cutaneous syndrome. Patients with this syndrome are distinctly presented with multiple tumors in the head and neck region, which can grow in size and number over time. Some of these benign head and neck tumors can turn into malignancies in some individuals. CYLD has been identified to be the only tumor suppressor gene reported to be associated with this syndrome thus far. Here, we summarize all reported CYLD germline mutations associated with this syndrome, as well as the reported paired somatic CYLD mutations of the developed tumors. Interestingly, whole-exome sequencing (WES) studies of multiple cancer types also revealed CYLD mutations in many human malignancies, including head and neck cancers and several epithelial cancers. Currently, the role of CYLD mutations in head and neck carcinogenesis and other cancers is poorly defined. We hope that this timely review of recent findings on CYLD genetics and animal models for oncogenesis can provide important insights into the mechanism of head and neck tumorigenesis.

Phenotype-genotype correlations for clinical variants caused by CYLD mutations

Brooke-Spiegler syndrome (BSS; OMIM 605041) is an autosomal dominant condition characterized by skin appendageal neoplasms including cylindromas, trichoepitheliomas, and/or spiradenomas. In 1996, the gene locus for BSS was mapped to 16q12-13, and, in 2000, mutations in the cylindromatosis (CYLD) gene were determined to cause BSS, familial cylindromatosis (FC; OMIM 132700) and multiple familial trichoepithelioma type 1 (MFT1; OMIM 601606). The CYLD gene encodes an enzyme with deubiquitinase activity. To date, a total of 95 different diseases-causing mutations have been published for the CYLD gene. A summary of mutations identified in Hungarian patients and a review of previously published mutations are presented in this update. The majority of the sequence changes are frameshift (48%), nonsense (27%), missense (12%) and splice-site (11%) mutations; however, two in-frame deletions have also been reported. Most mutations are located in exons 9-20. Analysis of the identified CYLD gene mutations and the observed BSS, FC and MFT1 clinical phenotypes of the patients revealed significant genotype-phenotype correlations. Elucidation of these genotype-phenotype correlations is critical for the diagnosis of these rare monogenic skin diseases. In addition, characterizing these correlations may promote the understanding of their mechanisms and may hopefully contribute to the development of future therapeutic modalities.

A novel frameshift mutation in the cylindromatosis (CYLD) gene in a Chinese family with multiple familial trichoepithelioma

Multiple familial trichoepithelioma (MFT) (OMIM: 601606) is an autosomal dominantly inherited disorder characterized by numerous, skin-colored papules and nodules with pilar differentiation. Recently, several mutations in the cylindromatosis (CYLD) gene have been reported in MFT. In this study, a mutation analysis of the CYLD was conducted in a Chinese pedigree of typical MFT. Affected individuals were identified through probands from Shanxi Province, China. Lesional skin biopsy of the proband revealed the typical histopathological characteristics of trichoepithelioma. Individuals belonging to five consecutive generations were similarly affected, which indicated an autosomal dominant inheritance pattern. Genomic DNA was extracted from peripheral blood lymphocytes using standard phenol/chloroform extraction method. All the coding exons (4-20) and exon-intron boundaries of the CYLD gene were amplified by polymerase chain reaction (PCR). Direct sequencing of all PCR products amplified from the complete coding regions of the CYLD gene was performed to identify mutations. Sequencing of the CYLD gene was performed in a further 100 unrelated, unaffected control individuals to exclude the possibility of polymorphism. A novel heterozygous frameshift mutation c.1169_1170delCA (p.Thr390Argfs) was identified in exon 10 of the CYLD gene in the affected family members. This mutation was also detected in unaffected family members, but not in the unrelated, healthy individuals who were also analyzed. Our study expands the database on the CYLD gene mutations in MFT and should be useful in providing genetic counseling and prenatal diagnosis for families affected by MFT.