Molecular diagnostics of ichthyoses using genodermatoses-dedicated next generation sequencing panel in Polish patients   

Ichthyoses are either syndromic or non-syndromic heterogeneous disorders manifesting by skin hyperkeratosis and scaling caused by inborn defects of epidermal barrier due to mutations in over 36 different genes. Genetic diversity and overlapping phenotypes are major issues explaining lack of molecular diagnostics in majority of Polish patients. 
Hence, the aim of the study were to elaborate cost effective genodermatoses-dedicated next generation sequencing (NGS) panel and to characterize molecularly 80 Polish patients with different subtypes of ichthyosis.
 
We used the self-designed panel of 86 genes. We used Roche NimbleGen SeqCap EZ System for library preparation and MiSeq sequencer (Illumina). Sanger sequencing or MLPA were used for mutations verification.   
 
We identified full genotype in 68 (85%) patients. In 4 (5%) patients we didn’t detect any mutation, while in 8 (10%) we found mutation in one allele only. Overall, we detected mutations in 19 distinct genes. In a subgroup of autosomal recessive congenital ichthyosis (ARCI, 30 people), mutations in ALOX12B and TGM1 accounted for 47% and 30%, respectively. In ALOX12B recurrent mutation p.Tyr521Cys was detected in 46% of alleles. Furthermore, three ARCI patients, in addition to their primary disease-causing mutations, harbor also FLG mutation in one allele.   
 
In conclusion, our panel proved to be an efficient and sensitive first-line diagnostic tool for ichthyosis patients. Our data provide further information regarding ichthyoses molecular epidemiology and also focus on the presence of secondary semi-dominant mutations in fillagrin (FLG) gene, which have important impact on genetic counseling and, presumably, may affect therapy.