A novel missense mutation of the CYLD gene identified in a Hungarian family with Brooke-Spiegler syndrome

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.

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.

Report of Three Novel Germline CYLD Mutations in Unrelated Patients with Brooke-Spiegler Syndrome, Including Classic Phenotype, Multiple Familial Trichoepitheliomas and Malignant Transformation

Brooke-Spiegler syndrome is a rare autosomal-dominant genetic disorder characterized by multiple adnexal tumors, including cylindromas, spiradenomas, spiradenocylindromas and trichoepitheliomas. It is caused by germline CYLD mutations commonly leading to a premature stop codon. We here report on 3 novel CYLD mutations in 3 unrelated BSS patients, including the classic phenotype, multiple familial trichoepitheliomas phenotype and malignant transformation. These included c.1821_1826+1delinsCT/L607Ffs*9, c.2666A>T/p.D889V and c.2712delT/p.905Kfs*8. By extending the spectrum of CYLD mutations, better understanding of the molecular mechanisms of BSS can be gained, which might later assist in finding new treatment options.

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.

Knowledge explosion for monogenic skin diseases

During the past few decades, the investigative tech-nologies of molecular biology - especially sequencing - underwent huge advances, leading to the sequencing of the entire human genome, as well as the identification of several candidate genes and the causative genetic variations that are responsible for monogenic skin diseases. These advances provided a solid basis for subsequent studies elucidating mechanisms of monogenic skin diseases and improving our understanding of common skin diseases. Furthermore, these discoveries also contributed to the development of novel therapeutic modalities for monogenic skin diseases. In this review, we have used the disease spectrum caused by mutations in the CYLD gene - Brooke-Spiegler syndrome, familial cylindromatosis and multiple familial trichoepithelioma type 1 - as a model for demonstrating the knowledge explosion for this group of diseases.

A novel CYLD germline mutation in Brooke-Spiegler syndrome

BACKGROUND

Brooke-Spiegler syndrome (BSS) is a rare, inherited, autosomal dominant disorder characterized by the development of multiple adnexal neoplasms including spiradenomas, cylindromas, trichoepitheliomas and major and minor salivary glands neoplasms. This syndrome encompasses a wide variability of clinical phenotypes depending on the variable number of tumours present in the given patient.

OBJECTIVE

Somatic mutations in adjunct to CYLD germline mutations may play a central role in the development of the tumour phenotype and in the genotype-phenotype correlations.

METHODS

Blood sample and paraffin embedded tissue biopsied from three cylindromas, one trichoepithelioma and one spiradenomas were collected after obtaining informed consent from our patient and genomic DNA was isolated.

RESULTS

We found out a novel germline mutation in the CYLD gene in exon 15 that resulted in the deletion of one nucleotide. This gives rise to a premature translational termination codon at amino acid position 693 prior to four Cys-X-X-Cys pairs and one of the two catalytic domains of ubiquitin carboxy-terminal hydrolases. In only one cylindroma we detected the same germline mutation (c.2070delT/p.F690FfsX3) in addition to two somatic events (I645V and R936X). The presence of this unique mutation could be linked to the peculiar phenotype of our patient who presented an attenuated form of BSS, an autosomal dominant inheritance with low penetrance and no additional visceral tumours.

CONCLUSIONS

The overall phenotype of our patient may support the hypothesis that somatic mutations in adjunct to CYLD germline mutations may play a central role in the development of the tumour phenotype and in the genotype-phenotype correlations.