The tumor-suppresor gene CYLD1 is located on 16q12-q13. It includes 20 exons whereas the first three of them are not translated. Its cDNA encodes 956 amino acids, however, there is also a truncated variant which lacks exon 7 and encodes a protein of 953 amino acids.

CYLD1 belongs to deubiquitinating enzymes. Its activity negatively regulates cytokine-mediated activation of NF-kappa-B kinase which is needed for a cellular homeostasis of accessory cutaneous organs (hair follicles, sebaceous glands, eccrine and apocrine glands). The loss of deubiquitinating activity of the CYLD1 gene increases resistancy to apoptosis and thereby correlates with tumor transformation.

Recently, there have been described mutations in this gene in Brooke-Spiegler syndrome, familial cylindromatosis and multiple familial trichoepithelioma. These, initially described separately, entities share some common clinical features and therefore, they are now considered as a single genetic syndrome with a different phenotype. Patients have a predispositions for multiple tumors of skin appendages such as cylindromas, spiroadenomas, spiradenocylindromas, trichoepitheliomas and other tumors of the skin and internal organs. Loss of heterozygosity (LOH) in the region of this gene were detected also in a significant amount of sporadic cylindromas.

The spectrum of mutations found in the gene CYLD1 is wide. In most cases germline mutations were detected, nevertheless, somatic mutations occurred as well. From the molecular genetic point of view these were the mutations caused by the frame-shift thanks to small insertions or deletions in the gene, substitution of bases leading to the formation of premature stop codon and mutations that alter a splice site. All of these mutations predicted truncated proteins.

Examination

In our laboratory, we perform DNA screening of all 20 exons of the gene CYLD1. DNA is isolated from the tissue (FFPE) or blood. Primers for PCR amplification are designed in order to be able to detect also a possible splice site mutation. The product is analyzed by direct sequencing (fig. 1).

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  Fig.1

  Mutation of the gene CYLD1. Insertion c.2170_2171insTC causing frame-shift mutation with premature stop codon p.K724IfsX12.

Clinical sensitivity:

According to the literature, CYLD gene mutations were found in about 85% cases of Brooke-Spiegler syndrome and about 45% cases with multiple familial trichepiteliosus (Grossmann et al., 2013). Direct sequencing of exons and exon-intron gene CYLD connections are able to detect approximately 95% of known mutations in this gene.

Analytical sensitivity and specificity of the sequencing of 99%.

Limitations:

Mutations deep in the introns and regulatory sequences are not detected. Deletions and duplications are not detected. Rare polymorphisms in the location of primers annealing may cause a diagnostic error.

In the case of the analysis of somatic mutations by sequencing the mutations will not be detected, if the altered cell line is not represented by at least 20%.

References

1. Biggs, P. J.; Chapman, P.; Lakhani, S. R.; Burn, J.; Stratton, M. R. : The cylindromatosis gene (cyld1) on chromosome 16q may be the only tumour suppressor gene involved in the development of cylindromas. Oncogene 12: 1375-1377, 1996.
2. Bignell, G. R.; Warren, W.; Seal, S.; Takahashi, M.; Rapley, E.; Barfoot, R.; Green, H.; Brown, C.; Biggs, P. J.; Lakhani, S. R.; Jones, C.; Hansen, J.; and 29 others : Identification of the familial cylindromatosis tumour-suppressor gene. Nature Genet. 25: 160-165, 2000.
3. Trompouki, E.; Hatzivassiliou, E.; Tsichritzis, T.; Farmer, H.; Ashworth, A.; Mosialos, G. : CYLD is a deubiquitinating enzyme that negatively regulates NF-kappa-B activation by TNFR family members. Nature 424: 793-796, 2003.
4. Young AL, Kellermayer R, Szigeti R, Teszas A, Azmi S, Celebi JT. CYLD mutations underlie Brooke-Spiegler, familial cylindromatosis, and multiple familial trichoepithelioma syndromes. Clin Genet. 2006 Sep;70(3):246-9.
5. Grossmann P, Vanecek T, Steiner P, Kacerovska D, Spagnolo DV, Cribier B, Rose C, Vazmitel M, Carlson JA, Emberger M, Martinek P, Pearce RL, Pearn J, Michal M,Kazakov DV. Novel and recurrent germline and somatic mutations in a cohort of 67 patients from 48 families with Brooke-Spiegler syndrome including the phenotypic variant of multiple familial trichoepitheliomas and correlation with the histopathologic findings in 379 biopsy specimens. Am J Dermatopathol. 2013;35(1):34-44.