Germline Mutation in EXPH5 Implicates the Rab27B Effector Protein Slac2-b in Inherited Skin Fragility

John A. McGrath, Kristina L. Stone, Rumena Begum, Michael A. Simpson, Patricia J. Dopping-Hepenstal, Lu Liu, James R. McMillan, Andrew P. South, Celine Pourreyron, W. H. Irwin McLean, Anna E. Martinez, Jemima E. Mellerio, Maddy Parsons

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    Abstract

    The Rab GTPase Rab27B and one of its effector proteins, Slac2-b (also known as EXPH5, exophilin-5), have putative roles in intracellular vesicle trafficking but their relevance to human disease is not known. By using whole-exome sequencing, we identified a homozygous frameshift mutation in EXPH5 in three siblings with inherited skin fragility born to consanguineous Iraqi parents. All three individuals harbor the mutation c.5786delC (p.Pro1929Leufs*8) in EXPH5, which truncates the 1,989 amino acid Slac2-b protein by 52 residues. The clinical features comprised generalized scale-crusts and occasional blisters, mostly induced by trauma, as well as mild diffuse pigmentary mottling on the trunk and proximal limbs. There was no increased bleeding tendency, no neurologic abnormalities, and no increased incidence of infection. Analysis of an affected person's skin showed loss of Slac2-b immunostaining (C-terminal antibody), disruption of keratinocyte adhesion within the lower epidermis, and an increased number of perinuclear vesicles. A role for Slac2-b in keratinocyte biology was supported by findings of cytoskeletal disruption (mainly keratin intermediate filaments) and decreased keratinocyte adhesion in both keratinocytes from an affected subject and after shRNA knockdown of Slac2-b in normal keratinocytes. Slac2-b was also shown to colocalize with Rab27B and beta 4 integrin to early adhesion initiation sites in spreading normal keratinocytes. Collectively, our findings identify an unexpected role for Slac2-b in inherited skin fragility and expand the clinical spectrum of human disorders of GTPase effector proteins.

    Original languageEnglish
    Pages (from-to)1115-1121
    Number of pages7
    JournalAmerican Journal of Human Genetics
    Volume91
    Issue number6
    DOIs
    Publication statusPublished - 7 Dec 2012

    Keywords

    • MYO5A
    • GRANULES
    • TRAFFICKING
    • MEMBRANE
    • MELANOPHILIN
    • CELLS
    • GTPASES
    • ASSOCIATION
    • GRISCELLI-SYNDROME
    • EXOSOMES

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    Cite this

    McGrath, J. A., Stone, K. L., Begum, R., Simpson, M. A., Dopping-Hepenstal, P. J., Liu, L., McMillan, J. R., South, A. P., Pourreyron, C., McLean, W. H. I., Martinez, A. E., Mellerio, J. E., & Parsons, M. (2012). Germline Mutation in EXPH5 Implicates the Rab27B Effector Protein Slac2-b in Inherited Skin Fragility. American Journal of Human Genetics, 91(6), 1115-1121. https://doi.org/10.1016/j.ajhg.2012.10.012