PIGT-CDG, a disorder of the glycosylphosphatidylinositol anchor: description of 13 novel patients and expansion of the clinical characteristics by Bayat, A, Knaus, A, Juul, A, Dukic, D, Gardella, E, Charzewska, A, Clement, E, Hjalgrim, H, Hoffman-Zacharska, D, Horn, D, Horton, R, Hurst, J, Josifova, D, Larsen, L, Lascelles, K, Obersztyn, E, Pagnamenta, A, Pal, D, Pendziwiat, M, Ryten, M, Taylor, J, Vogt, J, Weber, Y, Krawitz, P, Helbig, I, Kini, U, Møller, R, Ddd Study Group