Autosomal 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.¹ In Scandinavia, the prevalence is closer to one in 50 000.^2,3 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)).^4–9

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.^10–14

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.^2,12,15,16

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 α/β 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.¹¹

Mutations in either of …