A Coinheritance of X-Linked and Autosomal Dominant forms of the Ichthyosis

Alaverdian D1, Fedyakov M1, Polennikova E4, Ivashchenko T3, Sarana A1,2, Shcherbak S1,2, Urasov S1, Makarenko S1 and Glotov O*1-3 1Saint Petersburg City Hospital No.40, Russia, 197706, Saint Petersburg, Borisova street, 9. 2Saint Petersburg State University, Russian Federation, 199034, Saint Petersburg, Universitetskaya emb., 7/9 3D. O. Ott Research Institute of Obstetrics and Gynecology, Russia, 199034, Saint-Petersburg, Mendeleevskaya line, 3 4Family planning center “Medika”, Russian Federation, 194017, Saint Petersburg, Toreza pr., 72


Introduction
Inherited cornification diseases (ichthyosises) make up a large group of mendelian disorders which vary clinically and etiologically.
In general, all of them lead to the common feature -total or partial skin lesions which are caused by exfoliation or hyperkeratosis [1]. According to a modern classification, there are two forms of inherited ichthyosises: syndromic and nonsyndromic, each of them consists of more than ten different nosologies [1]. More common types of the ichthyosis are X-linked recessive (prevalence 1/2000-6000 in men) and autosomal dominant, or ichthyosis vulgaris with incomplete penetrance (1/250-1000) [2,3]. The X-linked form is associated with mutations in steroid sulfatase gene STS noteworthy there is a full deletion of the gene in 90% of cases [4][5][6]. Ichthyosis vulgaris is caused by heterozygous mutations in the gene FLG encoding filaggrin [3]. It is important to note that clinical forms of these diseases are indistinguishable [10]. The presented clinical case points out the necessity of molecular genetic testing even if the clinical diagnosis is clear.
According to a modern classification, there are two forms of inherited ichthyosises: syndromic and nonsyndromic, each of them consists of more than ten different nosologies [1]. More common types of the ichthyosis are X-linked recessive (prevalence 1/2000-6000 in men) and autosomal dominant, or ichthyosis vulgaris with incomplete penetrance (1/250-1000) [2,3]. The X-linked form is associated with mutations in steroid sulfatase gene STS noteworthy there is a full deletion of the gene in 90% of cases [4][5][6]. Ichthyosis vulgaris is caused by heterozygous mutations in the gene FLG encoding filaggrin [3]. It is important to note that clinical forms of these diseases are indistinguishable. The aim of this study was the searching for pathogenic or likely pathogenic mutations which associated with various forms of the inherited ichthyosis such as other inherited diseases with the similar phenotypic signs. The sequencing was held on HiSeq 4000 sequencer ("Illumina") by paired-end reading (2x150 bp). For the processing of the probes we used the method of selective capture of the coding DNA sequences "MedExome"[7]. The identified mutation p.Arg2037Ter in heterozygous condition was described before as pathogenic in data bases [9]. Also there was no coverage of STS gene sequence, which means that the patient has a full deletion of STS gene. Was found that the patient carries two pathogenic mutations which are related to different forms of the inherited ichthyosis. For the genetic counseling such information might be very valuable because of the clinical manifestation similarity. It is recommended to analyze both of genes STS and FLG to exclude the combined forms of ichthyosis.

Materials and Methods
A 40-year-old man was referred to our department for the genetic counseling. He had complaints to dry and flaky skin and had been suffering from ichthyosis since birth -skin problems had begun in the first month of life. The skin was covered by the dark scales.
The treatment had been selecting empirically and there wasn't any stable effect. The biopsy had taken place when he was 17 years old and indicated an increased level of cholesterine-3 sulfatase which led to diagnosis X-linked ichthyosis. The selected therapy consisted of a course taking vitamin A, a cream usage and an UV-based therapy and led to the improvement over the time. By the studying the family history it was revealed that the father was healthy, but the mother and the sister had been having problems with dry skin.
At the moment of the checkup obvious symptoms hadn't observed, although some dryness of skin covering had noticed mostly in the areas of the face and external hips surfaces (Figures 1 & 2), the nail plates was without any deformation or changes. It was considered to do the genetic analysis in order to verify the diagnosis and to compose the progeny forecast. We analyzed the patient DNA and two healthy donors (male and female) DNAs as controls.

Results/Observations
The NGS showed no coverage of the coding and flanking sequences of STS gene (    The identified mutation p.Arg2037Ter in heterozygous condition was described before as pathogenic in data bases [10]. The penetrance of this mutation is reduced and amounts to 90%. This amino acid substitution causes to the deficient protein synthesis and also is a nonsense mutation. Thus, the patient carries two pathogenic mutations which are related to different forms of the inherited ichthyosis. For the genetic counseling such information might be very valuable because of the clinical signs similarity. It is recommended to analyze both of genes STS and FLG to exclude the combined forms of ichthyosis.