Autosomal recessive congenital ichthyoses in the Czech Republic

Dear Editor, Autosomal recessive congenital ichthyosis (ARCI) represents a heterogeneous group of disorders of epidermal cornification. Nine genes have been identified to be causative of ARCI: TGM1,1 2 ABCA12,3 NIPAL4,4 CYP4F22,5 ALOX12B, ALOXE3,6 PNPLA1,7 LIPN8 and CERS3.9 ARCI is rare, with a reported prevalence of one in 200 000 in European and North American populations.10 We started DNA analysis of ARCI in 2012 when polymerase chain reaction direct sequencing of the TGM1, ALOX12B, ALOXE3, NIPAL4 and CYP4F22 genes was introduced and patients were analysed step by step for mutations in these genes. In 2014, we implemented the solution‐based capture method SeqCap EZ Choice Library (Roche NimbleGen, Madison, WI, U.S.A.) and targeted resequencing. A custom capture array was designed to capture exons and adjacent intron sequences of 81 genes associated with genodermatoses, of which 18 genes are associated with an ichthyosis phenotype. The genetic analyses were performed in 34 Czech ARCI probands: 11 patients (32%) carry mutations in ALOX12B, six (18%) in ALOXE3, six (18%) in NIPAL4, four (12%) in CYP4F22, three (9%) in TGM1, one (3%) in ABCA12 and three (9%) are without detectable causal mutations although all known genes up to now associated with ARCI were analysed (Table 1). Overall, mutations were identified in 31 patients (91%). Mutations identified in Czech probands with autosomal recessive congenital ichthyosis (ARCI) Mutations in bold letters were detected only in Czech patients with ARCI. Mutations identified in Czech probands with autosomal recessive congenital ichthyosis (ARCI) Mutations in bold letters were detected only in Czech patients with ARCI. To date, 42 different mutations have been described in the ALOX12B gene and 13 different mutations in the ALOXE3 gene (http://www.hgmd.cf.ac.uk/ac/index.php). In the set of Czech ARCI probands, we identified 11 patients with mutations in ALOX12B and six patients with mutations in ALOXE3. In total, 13 types of mutations were present in ALOX12B and five types in ALOXE3, of which eight and three, respectively, are novel and not described so far. Ten different mutations have been described in the NIPAL4 gene: seven missense, one nonsense, and two splicing (http://www.hgmd.cf.ac.uk/ac/index.php). We identified six patients carrying five types of NIPAL4 mutations, of which four are novel. One novel mutation is a missense mutation p.(Ser371Leu) while the other novel mutations are small duplications (c.1010_1015dupTCAGCA and c.1193dupT) and a deletion of one nucleotide (c.1063delC). At the present time, no deletions/duplications in the NIPAL4 gene have been identified. Three patients are homozygous for the identified mutations. Twelve different mutations of the CYP4F22 gene have been described (http://www.hgmd.cf.ac.uk/ac/index.php). We identified four patients with three types of CYP4F22 mutations, of which all are novel. One patient is homozygous for the mutation p.(Arg362Gln) and two patients for the mutation c.59dupG. In two unrelated patients with the genotype [c.59dupG];[c.59dupG], we performed haplotype linkage analysis. In view of our results we suppose the existence of a common ancestor in these two families, supporting a possible ‘founder effect’ connection with ARCI in the Czech Republic. At the present time, 147 different mutations have been detected in the TGM1 gene, of which 112 are missense (http://www.hgmd.cf.ac.uk/ac/index.php). We have three patients with TGM1 mutations. All patients have missense mutations, five types in total of which three are novel. Eighty‐two types of ABCA12 mutations have been described in http://www.hgmd.cf.ac.uk/ac/index.php. In our set of ARCI probands, we have one patient with mutations in the ABCA12 gene. This patient carries the novel mutation p.(Phe878Leu) and the mutation p.(Asn1380Ser), which has been described in patients with lamellar ichthyosis from five families from Morocco or Algeria.3 The causality of the mutation p.(Phe878Leu) is unclear; the prediction programs SIFT and PolyPhen‐2 designate this substitution as tolerated and benign, respectively. In each homozygous occurrence of a mutation, the patients' parents have no knowledge about their possible relationship. The genetic results were correlated with clinical findings (Table S1; see Supporting Information). From our 31 ARCI probands, 21 patients were classified as congenital ichthyosiform erythroderma (CIE), five patients as lamella ichthyosis (LI) and five patients as CIE/LI (showing characteristics of both CIE and LI). The proportion of particular phenotypes (CIE, LI, CIE/LI) in relation to a gene in which mutations were identified is as follows: 10 patients with CIE and one patient with CIE/LI in ALOX12B; four patients with CIE and two patients with CIE/LI in ALOXE3; two patients with CIE, two patients with CIE/LI, and two patients with LI in NIPAL4; four patients with CIE in CYP4F22; three patients with LI in TGM1; and one patient with CIE in ABCA12. None of the patients is being treated with retinoids. Histopathological analysis of skin tissue was performed in 17 patients. In all cases, light microscopy examination revealed nonspecific findings of epidermal hyperplasia, orthokeratotic hyperkeratosis, hyperkeratosis of follicular orifices, focal parakeratosis and a normal or thickened granular layer. The dermis often showed a mild superficial perivascular lymphocytic infiltration. Patient specimens were further analysed according to the ultrastructural findings and morphologically classified as ichthyosis congenita (IC) types I–IV where IC types I, III and IV correspond with CIE and IC type II with LI (Table S1; see Supporting Information).11 Immunohistochemical analysis demonstrated an absence of ALOX12B expression in patients with a mutated ALOX12B gene and severe deficiency in the case of patients with a mutated TGM1 gene. The frequency of mutations found in particular genes in the Czech ARCI population is different from those in other studies. For example, Fischer12 performed direct sequencing of TGM1, ALOX12B, ALOXE3, NIPAL4, CYP4F22 and ABCA12 in 520 ARCI families of different population origin. Fischer was able to identify mutations in all but 22% of patients: 32% of patients harboured mutations in TGM1, 12% in ALOX12B, 5% in ALOXE3, 16% in NIPAL4, 8% in CYP4F22 and 5% in ABCA12. Rodriguez‐Pazos et al.13 performed direct sequencing of TGM1, ALOX12B, ALOXE3, NIPAL4 and CYP4F22 in 16 Galician ARCI families. TGM1 mutations were found in 69% of patients, ALOXE3 mutations in 6%, and 25% were without mutations. Israeli et al.8 analysed 20 Israeli ARCI probands, of which 85% were born to related parents and were of non‐Jewish religious background: 30% of patients had TGM1 mutations, 20% ALOX12B mutations, 10% ALOXE3 mutations, 5% NIPAL4 mutations, 10% CYP4F22 mutations, 5% ABCA12 mutations, 5% LIPN mutations, and 15% were without genetic diagnosis. It is obvious that the frequency of TGM1 and ALOX12B mutations is different in the Czech ARCI population than in those studies: 32% vs. 12% in Fischer,12 69% vs. 0% in Rodriguez‐Pazos et al.13 and 30% vs. 20% in Israeli et al.,8 in contrast to 8.8% vs. 32.4% in our study. We would like to thank the physicians from the Departments of Medical Genetics (Drs Š. Prášilová, J. Šoukalová, Z. Kalina, P. Solařová, M. Simandlová, A.Puchmajerová, J. Hyjánek, A. Drahokoupilová and E. Kantorová) for providing us with their patients' blood samples and the MetaCentrum computing facilities (provided under program LM2010005 funded by the Ministry of Education, Youth, and Sports of the Czech Republic). H.B. and H.N. contributed equally to the paper as first authors. Funding sources: This study was supported by the project of the Internal Grant Agency of the Ministry of Health of the Czech Republic (NT/14585‐3); the project of the Ministry of Education, Youth, and Sports of the Czech Republic ‘CEITEC – Central European Institute of Technology’ (CZ.1.05/1.1.00/02.0068); and the project of the Technology Agency of the Czech Republic (TE02000058). Conflicts of interest: none declared. Table S1. Phenotypes of Czech patients with autosomal recessive congenital ichthyoses (ARCI).