- Genotype-phenotype studies in three families with mutations in the polyglutamine-binding protein 1 gene (PQBP1). Kleefstra, T., Franken, C.E., Arens, Y.H., Ramakers, G.J., Yntema, H.G., Sistermans, E.A., Hulsmans, C.F., Nillesen, W.N., van Bokhoven, H., de Vries, B.B., Hamel, B.C. Clin. Genet. (2004)