Goltz-Gorlin (focal dermal hypoplasia) and the microphthalmia with linear skin defects (MLS) syndrome: no evidence of genetic overlap

Abstract

Focal dermal hypoplasia (FDH) is an X-linked developmental disorder with male lethality characterized by patchy dermal hypoplasia, skeletal and dental malformations, and microphthalmia or anophthalmia. Recently, heterozygous loss-of-function mutations in the PORCN gene have been described to cause FDH. FDH shows some clinical overlap with the microphthalmia with linear skin defects (MLS) syndrome, another X-linked male lethal condition, associated with mutations of HCCS in the majority of cases. We performed DNA sequencing of PORCN in 13 female patients with the clinical diagnosis of FDH as well as four female patients with MLS syndrome and no mutation in HCCS. We identified PORCN mutations in all female patients with FDH. Eleven patients seem to have constitutional PORCN alterations in the heterozygous state and two individuals are mosaic for the heterozygous sequence change in PORCN. No PORCN mutation was identified in the MLS-affected patients, providing further evidence that FDH and MLS do not overlap genetically. X chromosome inactivation (XCI) analysis revealed a random or slightly skewed XCI pattern in leukocytes of individuals with intragenic PORCN mutation suggesting that defective PORCN does not lead to selective growth disadvantage, at least in leukocytes. We conclude that the PORCN mutation detection rate is high in individuals with a clear-cut FDH phenotype and somatic mosaicism can be present in a significant proportion of patients with mild or classic FDH.

Figure 1

Clinical features of FDH. Patients FDH11 (a–e), FDH1 (g), FDH6 (h–j), and FDH10 (k) show the typical clinical findings of FDH, such as dermal hypoplasia (leg of FDH 7 as newborn in (h) and at age 8 years in (i)), hyperpigmentation along the lines of Blaschko (c and i) and severe skeletal malformations, in particular syndactyly (d and e). Dysmorphic ears (b, j, and k) as well as dental defects such as oligodontia, hypodontia, enamel hypoplasia, and notched incisors (g) in FDH1. The father of patient FDH11 shows mild linear skin lesions on his calf (f).

Figure 2

Sequencing profiles from patients FDH4 (exon 3; left) and FDH7 (exon 14; right) with mosaic PORCN mutations. Top: profiles of directly sequenced PCR products suggestive of mosaicism for the c.268C>T mutation in FDH4 and c.1186C>T in FDH7. Middle: representative sequence of cloned PCR amplicons with wild-type sequence. Bottom: representative sequence of mutant cloned PCR products. The mutated and normal base is indicated by an orange arrow. Coding triplets and corresponding amino acid residues (one-letter code) are indicated.

Figure 3

The c.374-46T>A mutation in patient FDH5 introduced a novel splice acceptor site in PORCN intron 4. (a) Two of three splice site prediction programs failed to recognize the wild-type splice acceptor site, whereas the novel splice site yielded high scores by all three programs. (b) RT-PCR products were amplified from cDNA of patient FDH5 and two healthy individuals (C1 and C2) with primers located in PORCN exons 4 and 5. The normal 193-bp product is present in FDH5 and two controls, however, an additional amplicon of ∼240 bp was only amplified from the cDNA of FDH5 (white arrow). (c) Part of the sequence profile of the wild-type cloned RT-PCR amplicon (193 bp) of patient FDH5 showed splicing of exon 4 (ex 4) to exon 5 (ex 5). (d) Sequence analysis of the mutant cloned RT-PCR product (237 bp) revealed 44 bp of intron 4 spliced between exon 4 and 5. Coding triplets and corresponding amino acid residues (one-letter code) are indicated.