title: Brachydactyly Type C patient with compound heterozygosity for p.Gly319Val and p.Ile358Thr variants in the GDF5 proregion: benign variants or mutations?
abstract: We report on a Brachydactyly Type C (BDC) patient with clinically inconspicuous parents. Molecular genetic analyses revealed compound heterozygosity for two GDF5 variants. The variant c.956G>T (p.Gly319Val) was inherited from her mother and has been reported in exome sequencing projects, whereas c.1073T>C (p.Ile358Thr) has never been reported so far. In silico, both variants were predicted to be 'disease-causing', but the fact that p.Ile358Thr was predicted by SIFT to be 'tolerated' raised our suspicion. Therefore, we performed in vitro assays. To our surprise, GDF5(G319V) showed pronounced loss of function in luciferase reporter assays and in vitro chondrogenesis, whereas GDF5(I358T) and GDF5(WT) had comparable biological activities. Western blot analyses revealed decreased protein levels after overexpression of GDF5(G319V). In absence of linkage or de novo mutation, several scenarios could explain the underlying mechanism of the patient's phenotype. Owing to reduced activity of GDF5(G319V) in our functional assays, p.Gly319Val might be causative for BDC, but typically evoke an unrecognizably mild phenotype or even nonpenetrance. Another possibility is that our assays failed to pinpoint the disease-causing mechanism of the p.Ile358Thr allele. A final possibility is that compound heterozygosity for p.Ile358Thr and p.Gly319Val is more deleterious to GDF5 activity than either variant alone. Until all possible explanations can be rigorously tested experimentally, a precise recurrence risk counseling for the parents and the affected child is not possible.
authors.affiliation: Berlin Brandenburg Center for Regenerative Therapies (BCRT), Charité-Universitätsmedizin Berlin, Berlin, Germany.|Berlin Brandenburg School for Regenerative Therapies (BSRT), Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Stange
authors.affiliation: Institute for Medical Genetics and Human Genetics, Charité-Universitätsmedizin Berlin, Berlin, Germany.|Research Group Development and Disease, Max-Planck-Institute for Molecular Genetics, Berlin, Germany.
authors.forename: Claus-Eric
authors.initials: CE
authors.lastname: Ott
authors.affiliation: Berlin Brandenburg Center for Regenerative Therapies (BCRT), Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Mareen
authors.initials: M
authors.lastname: Schmidt-von Kegler
authors.affiliation: Institute for Human Genetics, Universitätsklinikum Essen, Essen, Germany.|Institute for Human Genetics, Universität zu Lübeck, Lübeck, Germany.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Gillesen-Kaesbach
authors.affiliation: Berlin Brandenburg Center for Regenerative Therapies (BCRT), Charité-Universitätsmedizin Berlin, Berlin, Germany.|Institute for Medical Genetics and Human Genetics, Charité-Universitätsmedizin Berlin, Berlin, Germany.|Research Group Development and Disease, Max-Planck-Institute for Molecular Genetics, Berlin, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mundlos
authors.affiliation: Institute for Medical Genetics and Human Genetics, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Katarina
authors.initials: K
authors.lastname: Dathe
authors.affiliation: Berlin Brandenburg Center for Regenerative Therapies (BCRT), Charité-Universitätsmedizin Berlin, Berlin, Germany.|Berlin Brandenburg School for Regenerative Therapies (BSRT), Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Petra
authors.initials: P
authors.lastname: Seemann
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D059327:Brachydactyly / Q000235:genetics*; D002675:Child, Preschool; D005260:Female; D005998:Glycine / Q000235:genetics; D055428:Growth Differentiation Factor 5 / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D007532:Isoleucine / Q000235:genetics; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D010375:Pedigree; D011401:Promoter Regions, Genetic / Q000235:genetics; D013912:Threonine / Q000235:genetics; D014633:Valine / Q000235:genetics
chemical_list: C525893:GDF5 protein, human; D055428:Growth Differentiation Factor 5; D007532:Isoleucine; D013912:Threonine; D014633:Valine; D005998:Glycine