Purpose: We aimed to assess the biological and clinical significance of the human cysteine protease inhibitor cystatin M/E, encoded by the CTS6 gene, in diseases of human hair and skin. Methods: Exome and Sanger sequencing was performed to reveal the genetic cause in two related patients with hypotrichosis. Immunohistochemical, biophysical, and biochemical measurements were performed on patient skin and 3D-reconstructed skin from patient-derived keratinocytes. Results: We identified a homozygous variant c.361C>T (p.Gln121*), resulting in a premature stop codon in exon 2 of CST6 associated with hypotrichosis, eczema, blepharitis, photophobia and impaired sweating. Enzyme assays using recombinant mutant cystatin M/E protein, generated by site-directed mutagenesis, revealed that this p.Gln121* variant was unable to inhibit any of its three target proteases (legumain and cathepsins L and V). Three-dimensional protein structure prediction confirmed the disturbance of the protease/inhibitor binding sites of legumain and cathepsins L and V in the p.Gln121* variant. Conclusion: The herein characterized autosomal recessive hypotrichosis syndrome indicates an important role of human cystatin M/E in epidermal homeostasis and hair follicle morphogenesis.

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Keywords 3D-reconstructed epidermis, hair follicle, proteases, skin barrier
Persistent URL dx.doi.org/10.1038/s41436-018-0355-3, hdl.handle.net/1765/112192
Journal Genetics in Medicine
van den Bogaard, E.H.J. (Ellen H. J.), van Geel, M, van Vlijmen-Willems, I.M.J.J. (Ivonne M. J. J.), Jansen, P, Peppelman, M. (Malou), van Erp, P.E.J. (Piet E. J.), … Zeeuwen, P.L.J.M. (Patrick L. J. M.). (2018). Deficiency of the human cysteine protease inhibitor cystatin M/E causes hypotrichosis and dry skin. Genetics in Medicine. doi:10.1038/s41436-018-0355-3