A splice donor site mutation in HOXD13 underlies synpolydactyly with cortical bone thinning

Inhibition of HOXD11 promotes cartilage degradation and induces osteoarthritis development

The 5'-HOXD genes are important for chondrogenesis in vertebrates, but their roles in osteoarthritis (OA) are still ambiguous. In our study, 5'-HOXD genes involvement contributing to cartilage degradation and OA was investigated. In bioinformatics analysis of 5'-HOXD genes, we obtained the GSE169077 data set related to OA in the GEO and analyzed DEGs using the GEO2R tool attached to the GEO. Then, we screened the mRNA levels of 5'-HOXD genes by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). We discovered that OA chondrocyte proliferation was inhibited, and apoptosis was increased. Moreover, it was discovered that SOX9 and COL2A1 were downregulated at mRNA and protein levels, while matrix metalloproteinases (MMPs) and a disintegrin-like and metalloproteinase with thrombospondin motifs (ADAMTSs) were upregulated. According to the results of differentially expressed genes (DEGs) and qRT-PCR, we evaluated the protein level of HOXD11 and found that the expression of HOXD11 was downregulated, reversed to MMPs and ADAMTSs but consistent with the cartilage-specific factors, SOX9 and COL2A1. In the lentivirus transfection experiments, HOXD11 overexpression reversed the effects in OA chondrocytes. In human OA articular cartilage, aberrant subchondral bone was formed in hematoxylin-eosin (H&E) and Safranin O and fast green (SOFG) staining results. Furthermore, according to immunohistochemistry findings, SOX9 and HOXD11 expression was inhibited. The results of this study established that HOXD11 was downregulated in OA cartilage and that overexpression of HOXD11 could prevent cartilage degradation in OA.

Recent Advances in Syndactyly: Basis, Current Status and Future Perspectives

A comprehensive summary of recent knowledge in syndactyly (SD) is important for understanding the genetic etiology of SD and disease management. Thus, this review article provides background information on SD, as well as insights into phenotypic and genetic heterogeneity, newly identified gene mutations in various SD types, the role of HOXD13 in limb deformities, and recently introduced modern surgical techniques for SD. This article also proposes a procedure for genetic analysis to obtain a clearer genotype-phenotype correlation for SD in the future. We briefly describe the classification of non-syndromic SD based on variable phenotypes to explain different phenotypic features and mutations in the various genes responsible for the pathogenesis of different types of SD. We describe how different types of mutation in HOXD13 cause various types of SD, and how a mutation in HOXD13 could affect its interaction with other genes, which may be one of the reasons behind the differential phenotypes and incomplete penetrance. Furthermore, we also discuss some recently introduced modern surgical techniques, such as free skin grafting, improved flap techniques, and dermal fat grafting in combination with the Z-method incision, which have been successfully practiced clinically with no post-operative complications.

A novel microdeletion upstream of HOXD13 in a Chinese family with synpolydactyly

Synpolydactyly (SPD) is a digital malformation with the typical clinical phenotype of the webbing of 3/4 fingers and/or 4/5 toes, and combined with polydactyly. In this study, we investigated a Chinese family with SPD and genetic analysis found that all of the affected individuals in the family carry a heterozygous 11,451 bp microdeletion at chr2:176933872-176945322 (GRCh37), which is located upstream of HOXD13 gene, the known disease gene for SPD1. All the affected individuals in the family carry the heterozygous deletion variant, and the variant co-segregated with SPD in the family. Thus, we speculate that the 11,451 bp microdeletion is the disease-causing variant in the family. To date, the microdeletion associating with SPD1 which we identified is the smallest deletion upstream of the HOXD13 gene and not altering the sequence of the HOXD13 gene.

Context-dependent HOX transcription factor function in health and disease

During animal development, HOX transcription factors determine the fate of developing tissues to generate diverse organs and appendages. The power of these proteins is striking: mis-expressing a HOX protein causes homeotic transformation of one body part into another. During development, HOX proteins interpret their cellular context through protein interactions, alternative splicing, and post-translational modifications to regulate cell proliferation, cell death, cell migration, cell differentiation, and angiogenesis. Although mutation and/or mis-expression of HOX proteins during development can be lethal, changes in HOX proteins that do not pattern vital organs can result in survivable malformations. In adults, mutation and/or mis-expression of HOX proteins disrupts their gene regulatory networks, deregulating cell behaviors and leading to arthritis and cancer. On the molecular level, HOX proteins are composed of DNA binding homeodomain, and large regions of unstructured, or intrinsically disordered, protein sequence. The primary roles of HOX proteins in arthritis and cancer suggest that mutations associated with these diseases in both the structured and disordered regions of HOX proteins can have substantial functional effects. These insights lead to new questions critical for understanding and manipulating HOX function in physiological and pathological conditions.

Mutations in the homeodomain of HOXD13 cause syndactyly type 1-c in two Chinese families

Background

Syndactyly type 1 (SD1) is an autosomal dominant limb malformation characterized in its classical form by complete or partial webbing between the third and fourth fingers and/or the second and third toes. Its four subtypes (a, b, c, and d) are defined based on variable phenotypes, but the responsible gene is yet to be identified. SD1-a has been mapped to chromosome 3p21.31 and SD1-b to 2q34–q36. SD1-c and SD1-d are very rare and, to our knowledge, no gene loci have been identified.

Methods and Results

In two Chinese families with SD1-c, linkage and haplotype analyses mapped the disease locus to 2q31-2q32. Copy number variation (CNV) analysis, using array-based comparative genomic hybridization (array CGH), excluded the possibility of microdeletion or microduplication. Sequence analyses of related syndactyly genes in this region identified c.917G>A (p.R306Q) in the homeodomain of HOXD13 in family A. Analysis on family B identified the mutation c.916C>G (p.R306G) and therefore confirmed the genetic homogeneity. Luciferase assays indicated that these two mutations affected the transcriptional activation ability of HOXD13. The spectrum of HOXD13 mutations suggested a close genotype-phenotype correlation between the different types of HOXD13-Syndactyly. Overlaps of the various phenotypes were found both among and within families carrying the HOXD13 mutation.

Conclusions

Mutations (p.R306Q and p.R306G) in the homeodomain of HOXD13 cause SD1-c. There are affinities between SD1-c and synpolydactyly. Different limb malformations due to distinct classes of HOXD13 mutations should be considered as a continuum of phenotypes and further classification of syndactyly should be done based on phenotype and genotype.