GLI3 variants causing isolated polysyndactyly are not restricted to the protein's C-terminal third.

Loss of function variants of GLI3 are associated with a variety of forms of polysyndactyly: Pallister-Hall syndrome (PHS), Greig-Cephalopolysyndactyly syndrome (GCPS), and isolated polysyndactyly (IPD). Variants affecting the N-terminal and C-terminal thirds of the GLI3 protein have been associated with GCPS, those within the central third with PHS. Cases of IPD have been attributed to variants affecting the C-terminal third of the GLI3 protein. In this study, we further investigate these genotype-phenotype correlations. Sequencing of GLI3 was performed in patients with clinical findings suggestive of a GLI3-associated syndrome. Additionally, we searched the literature for reported cases of either manifestation with mutations in the GLI3 gene. Here, we report 48 novel cases from 16 families with polysyndactyly in whom we found causative variants in GLI3 and a review on 314 previously reported GLI3 variants. No differences in location of variants causing either GCPS or IPD were found. Review of published data confirmed the association of PHS and variants affecting the GLI3 protein's central third. We conclude that the observed manifestations of GLI3 variants as GCPS or IPD display different phenotypic severities of the same disorder and propose a binary division of GLI3-associated disorders in either PHS or GCPS/polysyndactyly.

A novel missense in GLI3 possibly affecting one of the zinc finger domains may lead to postaxial synpolydactyly: case report.

BACKGROUND: Polydactyly is one of the most common congenital hand/foot malformations in humans. Mutations in GLI3 have been reported to cause syndromic and non-syndromic forms of preaxial and postaxial polydactylies. CASE PRESENTATION: The patient was a 2-year-old boy who underwent surgery in our hospital. The right hand and left foot of the patient were labelled as postaxial polydactyly type B, and there was cutaneous webbing between the 3rd and 4th fingers of the left hand. We identified a novel c. 1622C > T variant in GLI3 leading to an isolated postaxial synpolydactyly. CONCLUSIONS: The patient carries a novel autosomal dominant heterozygous missense mutation. This mutation c.1622C > T;p.(Thr541Met) in the GLI3 gene may affect the normal function of the zinc finger domain (ZFD) in a different way. However, it seems that more research is needed to determine the exact effects of this mutation.

Exome sequencing revealed a novel loss-of-function variant in the GLI3 transcriptional activator 2 domain underlies nonsyndromic postaxial polydactyly.

BACKGROUND: Polydactyly is a common genetic limb deformity characterized by the presence of extra fingers or toes. This anomaly may occur in isolation (nonsyndromic) or as part of a syndrome. The disease is broadly divided into preaxial polydactyly (PPD; duplication of thumb), mesoaxial polydactyly (complex polydactyly), and postaxial polydactyly (PAP: duplication of the fifth finger). The extra digits may be present in one or both the limbs. Heterozygous variants in the GLI3, ZRS/SHH, and PITX1 have been associated with autosomal dominant polydactyly, while homozygous variants in the ZNF141, IQCE, GLI1, and FAM92A have been associated with autosomal recessive polydactyly. Pathogenic mutations in the GLI3 gene (glioma-associated oncogene family zinc finger 3) have been associated with both nonsyndromic and syndromic polydactyly. METHODS: Here, we report an extended five generation kindred having 12 affected individuals exhibiting nonsyndromic postaxial polydactyly type A condition. Whole-exome sequencing followed by variant prioritization, bioinformatic studies, Sanger validation, and segregation analysis was performed. RESULTS: Using exome sequencing in the three affected individuals, we identified a novel heterozygous frameshift variant (c.3567_3568insG; p.Ala1190Glyfs*57) in the transcriptional activator (TA2) domain of the GLI3 encoding gene. CONCLUSION: To the best of our knowledge, the present study reports on the first familial case of nonsyndromic postaxial polydactyly due to the GLI3 variant in Pakistani population. Our study also demonstrated the important role of GLI3 in causing nonsyndromic postaxial polydactyly.

Structural basis of ßTrCP1-associated GLI3 processing.

Controlled ubiquitin-mediated protein degradation is essential for various cellular processes. GLI family regulates the transcriptional events of the sonic hedgehog pathway genes that are implicated in almost one fourth of human tumors. GLI3 phosphorylation by Ser/Thr kinases is a primary factor for their transcriptional activity that incurs the formation of both GLI3 repressor and activator forms. GLI3 processing is triggered in an ubiquitin-dependent manner via SCFßTrCP1 complex; however, structural characterization, mode of action based on sequence of phosphorylation signatures and induced conformational readjustments remain elusive. Here, through structural analysis and molecular dynamics simulation assays, we explored comparative binding pattern of GLI3 phosphopeptides against ßTrCP1. A comprehensive and thorough analysis demarcated GLI3 presence in the binding cleft shared by inter-bladed binding grooves of ß-propeller. Our results revealed the involvement of all seven WD40 repeats of ßTrCP1 in GLI3 interaction. Conversely, GLI3 phosphorylation pattern at primary protein kinase A (PKA) sites and secondary casein kinase 1 (CK1) or glycogen synthase kinase 3 (GSK3) sites was carefully evaluated. Our results indicated that GLI3 processing depends on the 19 phosphorylation sites (849, 852, 855, 856, 860, 861, 864, 865, 868, 872, 873, 876, 877, 880, 899, 903, 906, 907 and 910 positions) by a cascade of PKA, GSK3ß and CSKI kinases. The presence of a sequential phosphorylation in the binding induction of GLI3 and ßTrCP1 may be a hallmark to authenticate GLI3 processing. We speculate that mechanistic information of the individual residual contributions through structure-guided approaches may be pivotal for the rational design of specific and more potent inhibitors against activated GLI3 with a special emphasis on the anticancer activity.