De novo deletion of chromosome 18q in a baby with harlequin ichthyosis

Biallelic Mutations in KDSR Disrupt Ceramide Synthesis and Result in a Spectrum of Keratinization Disorders Associated with Thrombocytopenia

Mutations in ceramide biosynthesis pathways have been implicated in a few Mendelian disorders of keratinization, although ceramides are known to have key roles in several biological processes in skin and other tissues. Using whole-exome sequencing in four probands with undiagnosed skin hyperkeratosis/ichthyosis, we identified compound heterozygosity for mutations in KDSR, encoding an enzyme in the de novo synthesis pathway of ceramides. Two individuals had hyperkeratosis confined to palms, soles, and anogenital skin, whereas the other two had more severe, generalized harlequin ichthyosis-like skin. Thrombocytopenia was present in all patients. The mutations in KDSR were associated with reduced ceramide levels in skin and impaired platelet function. KDSR enzymatic activity was variably reduced in all patients, resulting in defective acylceramide synthesis. Mutations in KDSR have recently been reported in inherited recessive forms of progressive symmetric erythrokeratoderma, but our study shows that biallelic mutations in KDSR are implicated in an extended spectrum of disorders of keratinization in which thrombocytopenia is also part of the phenotype. Mutations in KDSR cause defective ceramide biosynthesis, underscoring the importance of ceramide and sphingosine synthesis pathways in skin and platelet biology.

Case report of de novo dup(18p)/del(18q) and r(18) mosaicism

This is a report of a 27-year-old woman with an unusual de novo chromosomal abnormality. Mosaicism was identified in peripheral blood cells examined by standard G-bands by trypsin using Giemsa (GTG) analysis and fluorescence in situ hybridization (FISH) analysis with chromosome-18 region-specific probes, 46,XX,del(18)(pter --> q21.33:)[41], 46,XX,r(18)(::p11.21 --> q21.33::)[8], and 46,XX,der(18)(pter --> q21.33::p11.21 --> pter)[1]. On the other hand, the karyotype of periodontal ligament fibroblasts was nonmosaic, 46,XX, der(18)(pter --> q21.33::p11.21 --> pter)[50]. All cell lines appeared to be missing a portion of 18q (q21.33 --> qter). The pattern of the dup(18p)/del(18q) in the rod configuration raises the possibility of an inversion in chromosome 18 in one of the parents. However, no chromosomal anomaly was detected in either parent. The most probable explanation is that de novo rod and ring configurations arose simultaneously from an intrachromosomal exchange. The unique phenotype of this patient, which included primary hypothyroidism and primary hypogonadism, is discussed in relation to her karyotype.

A review of harlequin ichthyosis

Harlequin ichthyosis is an extremely rare and historically lethal congenital disorder of the skin caused by abnormal keratinization. This article reviews the embryology and currently understood pathophysiology of the disease, as well as current methods used to diagnose and treat these infants. There are serious implications for the family to consider: the high risk that their newborn will die soon, as well as future family planning issues.

Avances biomoleculares en los trastornos epidérmicos hereditarios

In recent years, the genes responsible for many hereditary skin diseases have been discovered. These genes encode different proteins that participate in the terminal differentiation of the epidermis, so their alteration or absence causes a keratinization disorder and/or an increase in skin fragility. Thanks to genetic analyses, we have been able to understand the physiopathology of numerous genodermatoses and we have become closer to diagnosing many others. In the not-too-distant future, biomolecular techniques may foreseeably help us prevent and treat these processes, which include skin diseases as serious as epidermolysis bullosa or epidermolytic hyperkeratosis. In this article, we will study the most recent biomolecular findings referring to keratinization and epidermal disorders, mentioning the altered genes and/ or the defective proteins that cause them.

Epidermal-specific defect of GPI anchor in Pig-a null mice results in Harlequin ichthyosis-like features

We previously demonstrated that the epidermal-specific glycosylphosphatidylinositol (GPI)-anchor-deficient mice, generated by Pig-a gene disruption (Pig-a null mice), exhibited wrinkled and dry skin with hyperkeratosis and abnormal differentiation, and they died within a few days after birth. Here, we investigated the basis for the early demise of these animals, and the potential role of epidermal structural and biochemical abnormalities. The rapid demise of these animals was associated with both diminished epidermal permeability barrier function and decreased stratum corneum (SC) water content. The barrier abnormality could be attributed abnormal internal contents of lamellar bodies, with a downstream failure to generate normal extracellular lamellar bilayers in the SC. Moreover, processing profilaggrin to its monomeric form was impaired in Pig-a null mouse epidermis, while levels of the differentiation-specific proteins, involucrin, loricrin and profilaggrin were normal. Failure of filaggrin processing was accompanied by decreased activity of protein phosphatase 2A, an enzyme involved in profilaggrin to filaggrin processing. Thus, these studies demonstrate a critical role for GPI anchor and GPI-anchored proteins in divergent arms of epidermal terminal differentiation. While the permeability barrier abnormality can be attributed to defects in the lamellar body secretory system, the hydration abnormality is, in part, due to lack of availability of filaggrin-derived proteolytic products. Finally, since the dual abnormalities in the lamellar body secretory system and filaggrin processing resemble two key features of human Harlequin ichthyosis, Pig-a null mice could provide an appropriate analog for further studies of this disease.

The human cystatin M/E gene (CST6): exclusion candidate gene for harlequin ichthyosis

Cystatin M/E is a recently discovered cysteine proteinase inhibitor whose expression is largely confined to cutaneous epithelia. In human skin it is expressed in sweat glands, hair follicles, and stratum granulosum of the epidermis where it presumably acts as a substrate for transglutaminase. Very recently we reported that a null mutation in the mouse cystatin M/E gene (Cst6) causes the murine ichq phenotype, which is characterized by abnormalities in cornification and desquamation, demonstrating an essential role for cystatin M/E in the final stages of epidermal differentiation. We here obtained the complete sequence of the human cystatin M/E gene (CST6), which provides a tool to investigate CST6 as a candidate gene in skin diseases characterized by abnormal cornification. The involvement of CST6 in harlequin ichthyosis in humans was evaluated by sequencing the entire coding region and intron-exon boundaries for mutations in 11 sporadic harlequin ichthyosis patients. No CST6 mutations were detected in this group, which comprised type 1 and type 2 harlequin ichthyosis patients. Disturbed transcription/translation due to mutations in regulatory and noncoding regions of cystatin M/E was unlikely because cystatin M/E protein expression was observed in all patients examined, as assessed by immunohistochemistry. Although our results indicate that CST6 is not a major gene contributing to type 1 and 2 harlequin ichthyosis, these data may facilitate further analysis of the role of cystatin M/E in normal human skin and other genetic disorders of cornification.

18q-syndrome and ectodermal dysplasia syndrome: description of a child and his family

The 18q- syndrome [MIM #601808] is a terminal deletion of the long arm of chromosome 18. The most common deletion extends from region q21 to qter. We report here a nine-year-old boy possessing a simple 18q- deletion who had abnormalities of the brain, skull, face, tooth, hair, bone, and skin, plus joint laxity, tongue palsy, subtle sensoneural deafness, mental and speech delay, attention deficit hyperactivity disorder (ADHD), tic, and restless legs syndromes. His karyotype was 46, XY, del (18)(q21.31-qter). The size of the deletion was approximately 45 cM. Most of these abnormalities were not explained by the 18q- deletion. The family pedigree suggested the presence of a subtle involvement of ectodermal and/or mesodermal structures. Karyotypes of the other family members were normal.