LETTER TO JMG Assignment of the locus for ichthyosis prematurity syndrome to chromosome 9q33.3–34.13

A utosomal recessive congenital ichthyosis (ARCI) is a clinically and genetically heterogeneous group of inherited disorders of keratinisation, with an estimated incidence of one per 200 000 newborns. In Scandinavia, the prevalence is closer to one in 50 000. 3 By electron microscopy, ARCI can be classified into four subgroups—ichthyosis congenita I–IV—and one so far undefined group. Six loci have been associated with ARCI: on chromosomes 2q34 (LI2 (MIM 601277)), 3p21 (NCIE2 (MIM 604780)), 14q11.2 (LI1 (MIM 242300) and NCIE1 (MIM 242100)), 17p13.1 (LI5 (MIM 606545)), 19p12–q12 (LI3 (MIM 190195)), and 19p13.1–p13.2 (NNCI (MIM 604781)). Genes that correspond to four of these have been identified: the transglutaminase 1 gene (TGM1 (MIM 190195)) on chromosome 14q11, the comparative gene identification 58 (CGI-58 (MIM 604780)) on chromosome 3p21, two genes from the lipoxygenase (LOX) family— lipoxygenase-3 (ALOX3) and 12(R)-lipoxygenase (ALOX12B (MIM 603741))—on chromosome 17p13.1, and, most recently, the adenosine triphosphate binding cassette 12A (ABCA12A (MIM 607800)) on chromosome 2q34. The transglutaminase 1 protein takes part in the formation of the lipid envelope on the surface of epidermal keratinocytes. Cells with a disrupted TGM1 gene have a defective epidermal barrier function. TGM1 is altered in one third of patients with ichthyosis congenita type I and all patients with ichthyosis congenita type II. 12 15 16 Mutations in the CGI-58 gene on chromosome 3p21 cause Chanarin-Dorfman disease (CDS (MIM 275630)). The protein CGI-58 belongs to a large family of proteins characterised by an a/b hydrolase fold and contains three sequence motifs found in the esterase, lipase, and thioesterase subfamily. Affected patients have raised levels of triacylglycerol, and CGI-58 has been postulated to be involved in recycling of triacylglycerol derived monoacylglycerol or diacylglycerol to specific phospholipids or in the catabolism of long chain fatty acids. Mutations in either of the two lipoxygenase genes (ALOX3 and ALOX12B) on chromosome 17p13.1 result in a mild form of ARCI. The two genes are linked physically with a high sequence similarity, and they are related functionally. They are expressed mainly in epithelial cells, such as keratinocytes.LOX genes are involved in fatty acid metabolism and the maintenance of the cutaneous permeability barrier. Ichthyosis prematurity syndrome (IPS) is a distinct form of ARCI that is reported almost exclusively in the Norwegian population. 18 19 To date, the only exceptions are two Finnish families and one north Italian family. 21 It was observed as a unique syndrome because of its ultrastructural features of the skin and was published as ichthyosis congenita type IV. 22 The pattern on electron microscopy is characterised by membrane aggregations in the upper epidermal cells. Pregnancies with an affected foetus are complicated by polyhydramnion, and ultrasound shows opaque amniotic fluid. The birth is premature, and delivery usually takes place in weeks 30–32 of pregnancy. The child becomes severely asphyctic after delivery, probably because of aspiration of amnion debris. At birth, the skin, particularly on the head and peripheral extremities, is covered by a thick, caseous, desquamating epidermis, which, within two weeks, improves to a benign dryness of the skin. Later, the phenotype is mild, with persisting dryness of the skin and white scaling of the capilli. The skin shows a cobblestone like surface, particularly Key points