Mutations in CGI-58, the gene encoding a new protein of the esterase/lipase/thioesterase subfamily, in Chanarin-Dorfman syndrome

Abstract

Chanarin-Dorfman syndrome (CDS) is a rare autosomal recessive form of nonbullous congenital ichthyosiform erythroderma (NCIE) that is characterized by the presence of intracellular lipid droplets in most tissues. We previously localized a gene for a subset of NCIE to chromosome 3 (designated "the NCIE2 locus"), in six families. Lipid droplets were found in five of these six families, suggesting a diagnosis of CDS. Four additional families selected on the basis of a confirmed diagnosis of CDS also showed linkage to the NCIE2 locus. Linkage-disequilibrium analysis of these families, all from the Mediterranean basin, allowed us to refine the NCIE2 locus to an approximately 1.3-Mb region. Candidate genes from the interval were screened, and eight distinct mutations in the recently identified CGI-58 gene were found in 13 patients from these nine families. The spectrum of gene variants included insertion, deletion, splice-site, and point mutations. The CGI-58 protein belongs to a large family of proteins characterized by an alpha/beta hydrolase fold. CGI-58 contains three sequence motifs that correspond to a catalytic triad found in the esterase/lipase/thioesterase subfamily. Interestingly, CGI-58 differs from other members of the esterase/lipase/thioesterase subfamily in that its putative catalytic triad contains an asparagine in place of the usual serine residue.

Figure 1

A, Patient B3 at age 14 years, exhibiting typical phenotype of NCIE, with fine white scaling on erythrodermal background. B, Patient B8.2 at age 8 years, exhibiting small ears and abnormal pattern of hair distribution.

Figure 2

Common haplotypes in families from Tunisia (TN), Algeria (AL), Morocco (MO), Turkey (TR), and France (FR). Loss of homozygosity in family B4 is indicated by boxes. Bases are numbered beginning with the ATG initiation codon in exon 1 (A is at position 46 in cDNA sequence). Sequences for CNG (Centre National de Génotypage) microsatellite primers are available on request or from the Centre National de Génotypage website.

Figure 3

CGI-58 mutations in three patients with CDS and in their heterozygous parents. A, Mutation in acceptor splice site of exon 6. B, Point mutation at nucleotide 389, changing glutamine at position 130 to proline. C, Deletion of 2 bp at nucleotides 46/47, leading to frameshift and to premature stop codon at position 35. Arrowheads indicate the positions of the mutations.

Figure 4

RT-PCR of cultured lymphoblastoid cell lines from three patients and from their heterozygous parents. Patient B2 has a homozygous splice-site mutation, which reduces the size of the mRNA fragment. Both normal and altered mRNA fragments are detected in the heterozygous parent. The size of the normal mRNA fragment is 997 bp.