Fibulin-4: a novel gene for an autosomal recessive cutis laxa syndrome

Abstract

Cutis laxa is a condition characterized by redundant, pendulous, and inelastic skin. We identified a patient with recessive inheritance of a missense mutation (169G-->A; E57K) in the Fibulin-4 gene. She had multiple bone fractures at birth and was diagnosed with cutis laxa, vascular tortuosity, ascending aortic aneurysm, developmental emphysema, inguinal and diaphragmatic hernia, joint laxity, and pectus excavatum by age 2 years. Her skin showed markedly underdeveloped elastic fibers, and the extracellular matrix laid down by her skin fibroblasts contained dramatically reduced amounts of fibulin-4. We conclude that fibulin-4 is necessary for elastic fiber formation and connective tissue development.

Figure 1

Generalized cutis laxa and vascular tortuosity in the proband. Clinical photographs of the patient show sagging cheeks and tracheal tube (A), redundant skin in the extremities (B and C), and tortuous vessels in the periorbital area (arrows in D). In panel E, arrows point to a tortuous vein in the right upper chest area.

Figure 2

Skin pathology in the proband. A and B, Hematoxylin-eosin staining of samples from the patient (A) and an age- and sex-matched control (B) revealed increased vascularization (arrowheads) and reduced collagen bundle size (arrows) in the dermis of the patient. C and D, Hart’s elastin staining showed severely underdeveloped elastic fibers in both the papillary dermis (pd) (arrowheads) and the deep dermis (dd) (arrows) of the patient (C) compared with a matched control (D). There is no apparent pathology in the epidermis (ep). Magnification bars = 50 μm.

Figure 3

Recessive inheritance of E57K mutation in fibulin-4. A, DNA sequence analysis of FBLN4 revealed a homozygous 169G→A (E57K) mutation in the patient. Both parents were heterozygous, and a healthy control individual showed wild-type sequence (Wt). B, Multiple alignment of the peptide sequences of fibulins and fibrillin-1 shows the conservation of the E57 residue in all cbEGF-like modules. C, Three-dimensional structure of a pair of cbEGF modules, based on nuclear magnetic resonance studies of fibrillin-1 peptides, shows that the residue corresponding to E57 is part of the calcium-binding site.

Figure 4

Deficient matrix incorporation of K57 fibulin-4. Immunoblot analysis of fibulin-4 expression in fibroblasts from the patient (E57K) and three healthy controls (Wt 1–Wt 3). Cell lysates (Cell) show approximately equal expression of fibulin-4 in the patient and controls. However, EDTA extract of the extracellular matrix (ECM) shows no fibulin-4 in the patient sample.