An ADAMTSL2 Founder Mutation Causes Musladin-Lueke Syndrome, a Heritable Disorder of Beagle Dogs, Featuring Stiff Skin and Joint Contractures

Hannah L Bader,Alison L Ruhe,Dennis P O'Brien,Karl W Broman,Aaron K Wong,G Diane Shelton,Kathryn R Robertson,Suneel S Apte,Jonathan Mitelman,Kari F Walsh,Lauren W Wang,Mark W Neff,Rebecca A Packer

doi:10.1371/journal.pone.0012817

Abstract

BackgroundMusladin-Lueke Syndrome (MLS) is a hereditary disorder affecting Beagle dogs that manifests with extensive fibrosis of the skin and joints. In this respect, it resembles human stiff skin syndrome and the Tight skin mouse, each of which is caused by gene defects affecting fibrillin-1, a major component of tissue microfibrils. The objective of this work was to determine the genetic basis of MLS and the molecular consequence of the identified mutation.Methodology and Principal FindingsWe mapped the locus for MLS by genome-wide association to a 3.05 Mb haplotype on canine chromosome 9 (CFA9 (50.11–54.26; praw <10−7)), which was homozygous and identical-by-descent among all affected dogs, consistent with recessive inheritance of a founder mutation. Sequence analysis of a candidate gene at this locus, ADAMTSL2, which is responsible for the human TGFβ dysregulation syndrome, Geleophysic Dysplasia (GD), uncovered a mutation in exon 7 (c.660C>T; p.R221C) perfectly associated with MLS (p-value = 10−12). Murine ADAMTSL2 containing the p.R221C mutation formed anomalous disulfide-bonded dimers when transiently expressed in COS-1, HEK293F and CHO cells, and was present in the medium of these cells at lower levels than wild-type ADAMTSL2 expressed in parallel.Conclusions/SignificanceThe genetic basis of MLS is a founder mutation in ADAMTSL2, previously shown to interact with latent TGF-β binding protein, which binds fibrillin-1. The molecular effect of the founder mutation on ADAMTSL2 is formation of disulfide-bonded dimers. Although caused by a distinct mutation, and having a milder phenotype than human GD, MLS nevertheless offers a new animal model for study of GD, and for prospective insights on mechanisms and pathways of skin fibrosis and joint contractures.

Highlights

The critical role of extracellular matrix (ECM) in sequestration and regulated release or activation of growth factors is highly relevant to common medical problems such as fibrosis
The large latent complex (LLC) is sequestered in the ECM through binding of LTBP1 to the ECM glycoproteins fibrillin-1 and fibronectin [4,5,6,7]
We identified a missense founder mutation in ADAMTSL2 that causes Musladin-Lueke Syndrome (MLS), and have found that the mutation results in the formation of anomalous disulfide-bonded dimers

Summary

Introduction

The critical role of extracellular matrix (ECM) in sequestration and regulated release or activation of growth factors is highly relevant to common medical problems such as fibrosis. The three TGFb isoforms exist as disulfidebonded dimers [1] Their propeptides are processed intracellularly by furin, but remain associated with the active dimer (the latencyassociated peptide) [1] as the small latent complex (SLC), which in turn, binds to latent TGFb–binding protein (LTBP)-1, -3, and -4, to form a large latent complex (LLC) [1,2,3]. Musladin-Lueke Syndrome (MLS) is a hereditary disorder affecting Beagle dogs that manifests with extensive fibrosis of the skin and joints. In this respect, it resembles human stiff skin syndrome and the Tight skin mouse, each of which is caused by gene defects affecting fibrillin-1, a major component of tissue microfibrils. The objective of this work was to determine the genetic basis of MLS and the molecular consequence of the identified mutation

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Conclusion