Homozygous and compound heterozygous mutations in ZMPSTE24 cause the laminopathy restrictive dermopathy

Abstract

Restrictive dermopathy (RD) is a lethal human genetic disorder characterized by very tight, thin, easily eroded skin, rocker bottom feet, and joint contractures. This disease was recently reported to be associated with a single heterozygous mutation in ZMPSTE24 and hypothesized to be a digenic disorder (Navarro et al, Lamin A and ZMPSTE24 (FACE-1) defects cause nuclear disorganization and identify restrictive dermopathy as a lethal neonatal laminopathy. Hum Mol Genet 13:2493-2503, 2004). ZMPSTE24 encodes an enzyme necessary for the correct processing and maturation of lamin A, an intermediate filament component of the nuclear envelope. Here we present four unrelated patients with homozygous mutations in ZMPSTE24 and a fifth patient with compound heterozygous mutations in ZMPSTE24. Two of the three different mutations we found are novel, and all are single base insertions that result in messenger RNA frameshifts. As a consequence of the presumed lack of ZMPSTE24 activity, prelamin A, the unprocessed toxic form of lamin A, was detected in the nuclei of both cultured cells and tissue from RD patients, but not in control nuclei. Abnormally aggregated lamin A/C was also observed. These results indicate that RD is an autosomal recessive laminopathy caused by inactivating ZMPSTE24 mutations that result in defective processing and nuclear accumulation of prelamin A.

Figure 1. Family pedigrees, ZMPSTE24 genotypes, and sequence chromatograms.

Arrows indicate individuals whose DNA was tested. ZMPSTE24 mutations are shown below the pedigree symbols. (A) Pedigree of a consanguineous Dutch family; the father’s maternal grandmother and the mother’s paternal grandmother were sisters. The affected child had a homozygous thymidine duplication in ZMPSTE24 exon 9. (B) Sequence chromatograms of exon 9 (reverse direction) show a duplicated thymidine in a stretch of nine. Overlap of the normal and mutated strand sequences occurred after the insertion in this and in all the other heterozygous samples described below. (C) Pedigree of a nonconsanguineous American family carrying the same mutation as the Dutch family. (D) Pedigree from a consanguineous Guatemalan family; the father’s paternal grandfather was a paternal uncle of the mother. (E) Sequence chromatograms of exon 5 (forward direction) showing the duplicated thymidine in a stretch of seven. (F) Five affected children were born to two pairs of related parents from a Mennonite kindred; the fathers were brothers of each other, and the mothers were first cousins of each other. (G) Sequence chromatograms of ZMPSTE24 exon 1 (reverse direction) show an extra thymidine homozygous in the affected child.

Figure 2. Immunofluorescent localization of lamins A and C and prelamin A in control and RD patient fibroblasts.

(A) Confocal micrographs show localization of lamins A and C in nuclei of a control fibroblast and (B) a fibroblast from a RD patient. (C) Confocal micrographs show staining for prelamin A in a control fibroblast and (D) in a fibroblast from a RD patient.

Figure 3. Immunofluorescent localization of prelamin A and emerin in control tissue and tissue from a patient with RD.

(A) Prelamin A was undetectable in a kidney section from a normal patient but clearly present in nuclei in a liver section from a RD patient (B). (C) Nuclei in control cells and (D) in the RD patient’s cells are labeled with anti-emerin to show the presence of nuclear envelopes.