New splicing pathogenic variant in EBP causing extreme familial variability of Conradi-Hünermann-Happle Syndrome

Abstract

X-linked dominant chondrodysplasia punctata (CDPX2 or Conradi-Hünermann-Happle syndrome, MIM #302960) is caused by mutations in the EBP gene. Affected female patients present with Blaschkolinear ichthyosis, coarse hair or alopecia, short stature, and normal psychomotor development. The disease is usually lethal in boys. Nevertheless, few male patients have been reported; they carry a somatic mosaicism in EBP or present with Klinefelter syndrome. Here, we report CDPX2 patients belonging to a three-generation family, carrying the splice variant c.301 + 5 G > C in intron 2 of EBP. The grandfather carries the variant as mosaic state and presents with short stature and mild ichthyosis. The mother also presents with short stature and mild ichthyosis and the female fetus with severe limb and vertebrae abnormalities and no skin lesions, with random X inactivation in both. This further characterizes the phenotypical spectrum of CDPX2, as well as intrafamilial variability, and raises the question of differential EBP mRNA splicing between the different target tissues.

Fig. 1

Pedigree of the family with the different phenotypic features. III.1-Proband: 24 WG fetus, presenting with vertebral abnormalities and spinal puzzle, narrow thorax, chondral punctuations, and asymmetrical shortening of long bones. II.2-Mother: short stature, alopecia, coarse hair, xerosis. I.1-Grandfather: short stature, alopecia, coarse hair, ichthyosis, and asymmetrical length of the legs. Sanger analysis of EBP intron 2 showing the c.301 + 5 G > C variant at heterozygous state in the proband (III.1) and her mother (II.2), and at a mosaic state in the grandfather (I.1)

Fig. 2

Molecular characterization of the splicing defect EBP variant. a Ex vivo analysis of the c.301 + 5 G > C variant in EBP. Gel electrophoresis of RT-PCR products obtained from the minigene assay. Sanger sequencing resulting from the normal and the mutant splice site are represented. b RT-PCR products analysis obtained from the fetal tissue. Left: schematic representation of the genomic sequence surrounding the EBP variant. Black arrows correspond to the positions of the primers used for RT-PCR and sequencing. Right: Forward and reverse Sanger sequencing of the RT-PCR products obtained from the patient corresponding to different transcripts (mutated transcript 1 with skipping of the exon 2 and longer normal transcript 2 less amplified)