Copy-number mutations on chromosome 17q24.2-q24.3 in congenital generalized hypertrichosis terminalis with or without gingival hyperplasia

Abstract

Congenital generalized hypertrichosis terminalis (CGHT) is a rare condition characterized by universal excessive growth of pigmented terminal hairs and often accompanied with gingival hyperplasia. In the present study, we describe three Han Chinese families with autosomal-dominant CGHT and a sporadic case with extreme CGHT and gingival hyperplasia. We first did a genome-wide linkage scan in a large four-generation family. Our parametric multipoint linkage analysis revealed a genetic locus for CGHT on chromosome 17q24.2-q24.3. Further two-point linkage and haplotyping with microsatellite markers from the same chromosome region confirmed the genetic mapping and showed in all the families a microdeletion within the critical region that was present in all affected individuals but not in unaffected family members. We then carried out copy-number analysis with the Affymetrix Genome-Wide Human SNP Array 6.0 and detected genomic microdeletions of different sizes and with different breakpoints in the three families. We validated these microdeletions by real-time quantitative PCR and confirmed their perfect cosegregation with the disease phenotype in the three families. In the sporadic case, however, we found a de novo microduplication. Two-color interphase FISH analysis demonstrated that the duplication was inverted. These copy-number variations (CNVs) shared a common genomic region in which CNV is not reported in the public database and was not detected in our 434 unrelated Han Chinese normal controls. Thus, pathogenic copy-number mutations on 17q24.2-q24.3 are responsible for CGHT with or without gingival hyperplasia. Our work identifies CGHT as a genomic disorder.

Figure 1

Phenotypes and Genetic Mapping of Congenital Generalized Hypertrichosis Terminalis on Chromosome 17q24.2-q24.3 (A) A 60-year-old male (II-4 of family SY) showing excessive hair growth on his back and shoulders. (B) A 40-year-old bearded female (III-3 of family GD) showing a coarse face with bushy and dark eyebrows, a broad and flat nose, and thickened lips. (C) A 3-year-old boy (IV-3 of family GD) showing excessive hair growth on his back and limbs and a relative large head. (D) A 13-year-old bearded girl (II-2 of family BJ) showing a coarse face with bushy and dark eyebrows, long eyelashes, a bulbous soft nose, large ears with thick and hairy lobes, and thickened lips. (E) Genome-wide parametric multipoint linkage analysis in family SY yielded a maximum LOD score of 2.37 for SNPs from chromosome 17q24.2-q24.3. (F) Haplotype analysis of the three families (SY, GD, and BJ) with autosomal-dominant CGHT and coarse face. Recombinations in two affected individuals of SY (III-4 and IV-1), indicated by arrows, define a critical interval between markers D17S795 and D17S1351. The linked haplotype is boxed and the null alleles are indicated in red.

Figure 2

Identification of Inherited Microdeletions on Chromosome 17q24.2-q24.3 in Three CGHT Families (A) Copy-number state of a 5 Mb genomic region on chromosome 17q24.2-q24.3 in three affected individuals, one per family. (B) Real-time quantitative PCR (qPCR) assays of 11 amplicons validating the microdeletions. The deletion is seen as a ∼0.5-fold normalized relative copy number (RCN). Error bars represent SD. (C) Amplification of deletion junctions showing segregation of the microdeletions with the phenotypes in families SY, GD, and BJ. The sizes of long-range PCR fragments are shown. (D) Sequence analysis of the deletion junctions. The colored sequences represent the deletion junctions. The precise positions of the proximal and distal breakpoints are indicated in red and blue, respectively.

Figure 3

Identification of a De Novo Inverted Microduplication on Chromosome 17q24.2-q24.3 in KK (A) Photograph of KK showing extreme hair overgrowth. (B) Copy-number state of a 5 Mb genomic region on chromosome 17q24.2-q24.3 showing the presence of a microduplication in KK (green) but not in his parents (blue and red). (C) Eleven qPCR assays validating the microduplication in KK. The duplication is seen as a ∼1.5-fold RCN. Error bars represent SD. (D) The qPCR assay of the amplicon 7 confirming the de novo nature of the microduplication in KK. Error bars represent SD. (E) Two-color FISH of a representative interphase nucleus showing a “one fused red - one normal green” signal pattern. BAC probes are CTD-2331H1 (red), the most proximal fully duplicated BAC clone, and CTD-2309E11 (green). (F) Two-color FISH of a representative interphase nucleus showing a green-fused red-green signal order. BAC probes are CTD-2331H1 (red) and RP11-648L7 (green), the central duplicated BAC clone.

Figure 4

Schematic Diagram of the 17q24.2-q24.3 Region with a Summary of the Copy-Number Mutations Identified in the Present Study Positions of the RefSeq genes, microsatellite markers, BAC clones, and qPCR amplicons (vertical arrows 1–11) are shown. Open bars represent the sizes of the three microdeletions in affected individuals of families SY, GD, and BJ. Solid bars display the inverted microduplication in KK. Color bars indicate the positions and sizes of the BAC clones used in the two-color interphase FISH.