Brachydactyly Type C patient with compound heterozygosity for p.Gly319Val and p.Ile358Thr variants in the GDF5 proregion: benign variants or mutations?

Variable pulmonary manifestations in Chitayat syndrome: Six additional affected individuals

Hand hyperphalangism leading to shortened index fingers with ulnar deviation, hallux valgus, mild facial dysmorphism and respiratory compromise requiring assisted ventilation are the key features of Chitayat syndrome. This condition results from the recurrent heterozygous missense variant NM_006494.2:c.266A>G; p.(Tyr89Cys) in ERF on chromosome 19q13.2, encoding the ETS2 repressor factor (ERF) protein. The pathomechanism of Chitayat syndrome is unknown. To date, seven individuals with Chitayat syndrome and the recurrent pathogenic ERF variant have been reported in the literature. Here, we describe six additional individuals, among them only one presenting with a history of assisted ventilation, and the remaining presenting with variable pulmonary phenotypes, including one individual without any obvious pulmonary manifestations. Our findings widen the phenotype spectrum caused by the recurrent pathogenic variant in ERF, underline Chitayat syndrome as a cause of isolated skeletal malformations and therefore contribute to the improvement of diagnostic strategies in individuals with hand hyperphalangism.

Cystine knot growth factors and their functionally versatile proregions

The cystine knot disulfide pattern has been found to be widespread in nature, since it has been detected in proteins from plants, marine snails, spiders and mammals. Cystine knot proteins are secreted proteins. Their functions range from defense mechanisms as toxins, e.g. ion channel or enzyme inhibitors, to hormones, blood factors and growth factors. Cystine knot proteins can be divided into two superordinate groups. (i) The cystine knot peptides, also referred to - with other non-cystine knot proteins - as knottins, with linear and cyclic polypeptide chains. (ii) The cystine knot growth factor family, which is in the focus of this article. The disulfide ring structure of the cystine knot peptides is made up by the half-cystines 1-4 and 2-5, and the threading disulfide bond is formed by the half-cystines, 3-6. In the growth factor group, the disulfides of half-cystines 1 and 4 pass the ring structure formed by the half-cystines 2-5 and 3-6. In this review, special emphasis will be devoted to the growth factor cystine knot proteins and their proregions. The latter have shifted into the focus of scientific interest as their important biological roles are just to be unravelled.

Chimerism for 20q11.2 microdeletion of GDF5 explains discordant phenotypes in monochorionic-diamniotic twins

Microdeletions of 20q11.2 are rare but have been associated with characteristic clinical findings. A 1.6 Mb minimal critical region has been identified that includes three OMIM genes: GDF5, EPB41L1, and SAMHD. Here we describe a male monozygotic, monochorionic-diamniotic twin pair with discordant phenotypes, one with multiple findings that overlap with those reported in 20q11.2 deletions, and the other unaffected. Microarray analysis revealed mosaicism for a 363 Kb deletion encompassing GDF5 in the peripheral blood of both twins, which was confirmed by FISH. Subsequent FISH on buccal cells identified the deletion only in the affected twin. The blood FISH findings were interpreted as representing chimerism resulting from anastomosis and the blood exchange between the twins in utero. The implications of this finding are discussed, as is the contribution of GDF5 to the associated clinical findings of 20q11.2 deletions.