Localization of the Netherton syndrome gene to chromosome 5q32, by linkage analysis and homozygosity mapping

Abstract

Netherton syndrome (NS [MIM 256500]) is a rare and severe autosomal recessive disorder characterized by congenital ichthyosis, a specific hair-shaft defect (trichorrhexis invaginata), and atopic manifestations. Infants with this syndrome often fail to thrive; life-threatening complications result in high postnatal mortality. We report the assignment of the NS gene to chromosome 5q32, by linkage analysis and homozygosity mapping in 20 families affected with NS. Significant evidence for linkage (maximum multipoint LOD score 10.11) between markers D5S2017 and D5S413 was obtained, with no evidence for locus heterogeneity. Analysis of critical recombinants mapped the NS locus between markers D5S463 and D5S2013, within an <3.5-cM genetic interval. The NS locus is telomeric to the cytokine gene cluster in 5q31. The five known genes encoding casein kinase Ialpha, the alpha subunit of retinal rod cGMP phosphodiesterase, the regulator of mitotic-spindle assembly, adrenergic receptor beta2, and the diastrophic dysplasia sulfate-transporter gene, as well as the 38 expressed-sequence tags mapped within the critical region, are not obvious candidates. Our study is the first step toward the positional cloning of the NS gene. This finding promises a better understanding of the molecular mechanisms that control epidermal differentiation and immunity.

Figure 1

A, Child with NS, showing redness and peeling of skin, especially around the mouth and the eyes, and sparse and fragile hair. B, Light-microscopic aspect of scalp hair with trichorrhexis invaginata.

Figure 2

A, Multipoint linkage analysis of a 40-cM region encompassing the NS locus on 5q32. Markers D5S2017 and D5S413 (blackened arrowheads) delineate a 5.4-cM region of linkage in which multipoint LOD scores (LOD) are >3.0. The multipoint Z_max, 10.11, was obtained with marker D5S434 (unblackened arrowhead). B, Radiation-hybrid map of NS locus. The map is oriented centromeric (cen [top]) to telomeric (tel [bottom]). The physical distances (cR) between the NS locus and each marker are indicated on the left; we based them on either the radiation-hybrid map of chromosome 5 (Whitehead Institute for Biomedical Research/MIT Center for Genome Research) or our radiation-hybrid mapping results with the Genebridge 4 panel (asterisks). The genetic distances (cM) between the markers, according to the Généthon human linkage map, are shown on the right. Notably, the positions of markers D5S2099/D5S436 and D5S434/D5S413 are slightly discordant between the two maps. The NS critical interval is denoted by the thicker vertical line.

Figure 3

Pedigree structure and haplotype analysis of representative families with NS (A) and critical recombination events (B). Haplotypes for 26 polymorphic markers on 5q are shown. Markers are ordered centromeric (top) to telomeric (bottom), according to the Généthon human linkage map, except markers D5S2099 to D5S470, which have been ordered on the basis of our radiation-hybrid mapping results and the radiation-hybrid map of chromosome 5 (Whitehead Institute for Biomedical Research/MIT Center for Genome Research). Markers used for the initial genomewide scan are underlined. Disease-linked haplotypes are boxed. Noninformative markers are gray shaded. A, Families 1, 6, and 7, which were included in the initial genomewide search for linkage. In each family, affected offspring share the same genotype at the NS locus. In affected individual 1.3, a maternal recombination event places the NS locus centromeric to D5S636. Markers D5S2013, BT1, and CSF1R are not informative for recombination localization in this individual. In families 6 and 7, the fathers (6.2 and 7.1) are half-brothers, and the mothers (6.1 and 7.2) are first cousins. The haplotype shared by descent is boxed, in the case of the fathers, and cross-hatched, in the case of the mothers. Interestingly, the affected offspring (6.5, 7.3, and 7.4) are homozygous for the same disease-associated haplotype, from D5S2115 to D5S2015, suggesting identity by descent, possibly due to a founder ancestor. B, Critical recombination events occurring in families 3 and 12. Only key individuals are shown. Haplotype analysis in unaffected individual 3.12 locates the NS locus proximal to marker D5S2013, although marker D5S413 is not fully informative. Haplotype analysis of affected individual 12.10 places the NS locus distal to marker D5S463, although markers D5S2090 and D5S434 are not fully informative. The NS critical region is indicated by the thickest vertical line.