Identification of a novel heterozygous truncation mutation in exon 1 of ARHGAP29 in an Indian subject with nonsyndromic cleft lip with cleft palate

Four putative pathogenic ARHGAP29 variants in patients with non-syndromic orofacial clefts (NsOFC)

The pathophysiological basis of non-syndromic orofacial cleft (NsOFC) is still largely unclear. However, exome sequencing (ES) has led to identify several causative genes, often with reduced penetrance. Among these, the Rho GTPase activating protein 29 (ARHGAP29) has been previously implicated in 7 families with NsOFC. We investigated a cohort of 224 NsOFCs for which no genetic pathogenic variant had been identified by diagnostic testing. We used ES and bioinformatic variant filtering and identified four novel putative pathogenic variants in ARHGAP29 in four families. One was a missense variant leading to the substitution of the first methionine with threonine, two were heterozygous frameshift variants leading to a premature termination codon, and one was a nonsense variant. All variants were predicted to result in loss of function, either through mRNA decay, truncated ARHGAP29, or abnormal N-terminal initiation of translation of ARHGAP29. The truncated ARHGAP29 proteins would lack the important RhoGAP domain. The variants were either absent or rare in the control population databases, and the loss of intolerance score (pLI) of ARHGAP29 is 1.0, suggesting that ARHGAP29 haploinsufficiency is not tolerated. Phenotypes ranged from microform cleft lip (CL) to complete bilateral cleft lip and palate (CLP), with one unaffected mutation carrier. These results extend the mutational spectrum of ARHGAP29 and show that it is an important gene underlying variable NsOFC phenotypes. ARHGAP29 should be included in diagnostic genetic testing for NsOFC, especially familial cases, as it may be mutated in ∼4% of them (4/97 in our cohort) with high penetrance (89%).

From Bedside to Bench and Back: Advancing Our Understanding of the Pathophysiology of Cleft Palate and Implications for the Future

OBJECTIVE

To provide a comprehensive understanding of the pathophysiology of cleft palate (CP) and future perspectives.

DESIGN

Literature review.

SETTING

Setting varied across studies by level of care and geographical locations.

INTERVENTIONS

No interventions were performed.

MAIN OUTCOME MEASURE(S)

Primary outcome measures were to summarize our current understanding of palatogenesis in humans and animal models, the pathophysiology of CP, and potential future treatment modalities.

RESULTS

Animal research has provided considerable insight into the pathophysiology, molecular and cellular mechanisms of CP that have allowed for the development of novel treatment strategies. However, much work has yet to be done to connect our mouse model investigations and discoveries to CP in humans. The success of innovative strategies for tissue regeneration in mice provides promise for an exciting new avenue for improved and more targeted management of cleft care with precision medicine in patients. However, significant barriers to clinical translation remain. Among the most notable challenges include the differences in some aspects of palatogenesis and tissue repair between mice and humans, suggesting that potential therapies that have worked in animal models may not provide similar benefits to humans.

CONCLUSIONS

Increased translation of pathophysiological and tissue regeneration studies to clinical trials will bridge a wide gap in knowledge between animal models and human disease. By enhancing interaction between basic scientists and clinicians, and employing our animal model findings of disease mechanisms in concert with what we glean in the clinic, we can generate a more targeted and improved treatment algorithm for patients with CP.

Targeted re-sequencing on 1p22 among non-syndromic orofacial clefts from Han Chinese population

Rs560426 at 1p22 was proved to be associated with NSCL/P (non-syndromic cleft lip with or without the palate) in several populations, including Han Chinese population. Here, we conducted a deep sequencing around rs560426 to locate more susceptibility variants in this region. In total, 2,293 NSCL/P cases and 3,235 normal controls were recruited. After sequencing, association analysis was performed. Western blot, RT-qPCR, HE, immunofluorescence staining, and RNA sequencing were conducted for functional analyses of the selected variants. Association analysis indicated that rs77179923 was the only SNP associated with NSCLP specifically (p = 4.70E-04, OR = 1.84), and rs12071152 was uniquely associated with LCLO (p = 4.00E-04, OR = 1.30, 95%CI: 1.12–1.51). Moreover, de novo harmful rare variant NM_004815.3, NP_004806.3; c.1652G>C, p.R551T in ARHGAP29 resulted in a decreased expression level of ARHGAP29, which in turn affected NSCL/P-related biological processes; however, no overt cleft palate (CP) phenotype was observed. In conclusion, rs12071152 was a new susceptible variant, which is specifically associated with LCLO among the Han Chinese population. Allele A of it could increase the risk of having a cleft baby. Rs77179923 and rare variant NM_004815.3, NP_004806.3; c.1652G>C, p.R551T at 1p22 were both associated with NSCLP among the Han Chinese population. However, this missense variation contributes to no overt CP phenotype due to dosage insufficiency or compensation from other genes.

KDM6B interacts with TFDP1 to activate P53 signalling in regulating mouse palatogenesis

Epigenetic regulation plays extensive roles in diseases and development. Disruption of epigenetic regulation not only increases the risk of cancer, but can also cause various developmental defects. However, the question of how epigenetic changes lead to tissue-specific responses during neural crest fate determination and differentiation remains understudied. Using palatogenesis as a model, we reveal the functional significance of Kdm6b, an H3K27me3 demethylase, in regulating mouse embryonic development. Our study shows that Kdm6b plays an essential role in cranial neural crest development, and loss of Kdm6b disturbs P53 pathway-mediated activity, leading to complete cleft palate along with cell proliferation and differentiation defects in mice. Furthermore, activity of H3K27me3 on the promoter of Trp53 is antagonistically controlled by Kdm6b, and Ezh2 in cranial neural crest cells. More importantly, without Kdm6b, the transcription factor TFDP1, which normally binds to the promoter of Trp53, cannot activate Trp53 expression in palatal mesenchymal cells. Furthermore, the function of Kdm6b in activating Trp53 in these cells cannot be compensated for by the closely related histone demethylase Kdm6a. Collectively, our results highlight the important role of the epigenetic regulator KDM6B and how it specifically interacts with TFDP1 to achieve its functional specificity in regulating Trp53 expression, and further provide mechanistic insights into the epigenetic regulatory network during organogenesis.

Identification of a Novel Variant of ARHGAP29 in a Chinese Family with Nonsyndromic Cleft Lip and Palate

Background

Cleft lip with or without cleft palate (CL/P) is the most common facial birth defect, with a worldwide incidence of 1 in 700-1000 live births. CL/P can be divided into syndromic CL/P (SCL/P) and nonsyndromic CL/P (NSCL/P). Genetic factors are an important component to the etiology of NSCL/P. ARHGAP29, one of the NSCL/P disease-causing genes, mediates the cyclical regulation of small GTP binding proteins such as RhoA and plays an essential role in cellular shape, proliferation, and craniofacial development.

Methods

The present study investigated a Chinese family with NSCL/P and explored potential pathogenic variants using whole-exome sequencing (WES). Variants were screened and filtered through bioinformatic analysis and prediction of variant pathogenicity. Cosegregation was subsequently conducted.

Results

We identified a novel heterozygous missense variant of ARHGAP29 (c.2615C > T, p.A872V) in a Chinese pedigree with NSCL/P.

Conclusion

We detected the disease-causing variant in this NSCL/P family. Our identification expands the genetic spectrum of ARHGAP29 and contributes to novel approaches to the genetic diagnosis and counseling of CL/P families.

A novel splicing mutation of ARHGAP29 is associated with nonsyndromic cleft lip with or without cleft palate

BACKGROUND

Nonsyndromic cleft lip with or without cleft palate (NSCL/P) is one of the most common birth defects, and occurs in approximately 1/700 live births worldwide. The correlation between the ABCA4-ARHGAP29 region and NSCL/P was first identified by genome-wide association studies (GWAS), but few reports have examined NSCL/P caused by ARHGAP29 mutations in the Chinese population.

METHODS

We performed chromosome microarray analysis (CMA) for two consecutive abnormal fetuses and whole exome sequencing (WES) for the family, including 3 patients and 2 normal family members, Sanger sequencing and RT-PCR were used to confirm the mutation.

RESULTS

We identified a novel splice donor mutation (ARHGAP29 c.1920 + 1G > A) in two consecutive NSCL/P fetuses, and the variant was inherited from the mother and grandfather. The mutation caused abnormal skipping of exon 17, and the mRNA level of ARHGAP29 was significantly decreased compared to the wild type.

CONCLUSIONS

In this study, we successfully diagnosed the genetic cause of NSCL/P in a family and first report that the c.1920 + 1G > A mutation in ARHGAP29 is associated with NSCL/P. Our study enriches the genetic landscape of NSCL/P, extends the mutation spectrum of ARHGAP29, and provides a new direction for the diagnosis of NSCL/P in patients and its prenatal diagnosis in fetuses.

The SNP rs560426 Within ABCA4-ARHGAP29 Locus and the Risk of Nonsyndromic Oral Clefts

OBJECTIVE

Nonsyndromic oral clefts are common birth defect with complex etiology. In the present study, we attempt to further validate the possible role for ABCA4 and ARHGAP29 in the susceptibility to nonsyndromic oral clefts.

DESIGN

We performed allelic transmission disequilibrium test analysis, on 10 eligible single nucleotide polymorphisms (SNPs) and SNP haplotypes using the Family-Based Association Test.

PARTICIPANTS

The study sample consisted of 334 case-parent trios of nonsyndromic oral clefts from Taiwanese population, separated into nonsyndromic cleft lip with or without cleft palate (NSCL/P) and nonsyndromic cleft palate only (NSCPO) groups.

RESULTS

We found only the SNP rs560426 within the ABCA4 gene showed strong association with NSCPO (P = .03498; Permuted P = .05382). No association between other 9 selected SNPs in ABCA4-ARHGAP29 region and the risk of nonsyndromic oral clefts was found. For the haplotype analyses, we found only haplotype T-C (rs570926 and rs3789431) in ABCA4 block 2 showed significant association with nonsyndromic NSCL/P in these Taiwanese trios.

CONCLUSIONS

We used a family-based analysis in 334 Taiwanese case-parent trios to validate the possible role for ABCA4 and ARHGAP29 in the susceptibility to nonsyndromic oral clefts. This study provides a new evidence for an association between the intron variant rs560426 within ABCA4 and nonsyndromic cleft palate which may contribute their regulatory role in craniofacial development.

Hypoxia suppresses myofibroblast differentiation by changing RhoA activity

Fibroblasts show a high range of phenotypic plasticity, including transdifferentiation into myofibroblasts. Myofibroblasts are responsible for generation of the contraction forces that are important for wound healing and scar formation. Overactive myofibroblasts, by contrast, are involved in abnormal scarring. Cell stretching and extracellular signals such as transforming growth factor β can induce the myofibroblastic program, whereas microenvironmental conditions such as reduced tissue oxygenation have an inhibitory effect. We investigated the effects of hypoxia on myofibroblastic properties and linked this to RhoA activity. Hypoxia reversed the myofibroblastic phenotype of primary fibroblasts. This was accompanied by decreased αSMA (ACTA2) expression, alterations in cell contractility, actin reorganization and RhoA activity. We identified a hypoxia-inducible induction of ARHGAP29, which is critically involved in myocardin-related transcription factor-A (MRTF-A) signaling, the differentiation state of myofibroblasts and modulates RhoA activity. This novel link between hypoxia and MRTF-A signaling is likely to be important for ischemia-induced tissue remodeling and the fibrotic response.This article has an associated First Person interview with the first author of the paper.

Genetic variants of MGMT, RHPN2, and FAM49A contributed to susceptibility of nonsyndromic orofacial clefts in a Chinese population

BACKGROUND

The role of underlying genetic factors in the pathogenesis of nonsyndromic orofacial clefts (NSOC) remains poorly understood. Although genomewide association studies (GWASs) of NSOC have successfully identified a large number of novel genetic risk loci, association results of replication studies are inconsistent across different populations.

METHODS

Six single nucleotide polymorphisms (SNPs) (rs7922405 at 10q26.3, rs73039426 at 19q13.11, rs7552 at 2p24.2, rs1788160 at 8q22.2, rs9381107 at 6p24.3, and rs17095681 at 10q25.3) were analyzed for an association with NSOC in 1062 participants of Chinese descent (596 patients and 466 controls). We applied the multifactor dimensionality reduction (MDR) method to detect potential gene-gene (G × G) interactions in the six SNPs.

RESULTS

The genotype or allele frequencies of SNPs rs7922405, rs73039426, and rs7552 showed significant differences between the controls and patients with NSOC, whereas no association was shown between three SNPs (rs1788160, rs17095681, and rs9381107) and NSOC. MDR analysis did not reveal significant G × G interactions for susceptibility to NSOC.

CONCLUSION

We confirmed that three genes (rs7922405 of MGMT, rs73039426 of RHPN2, and rs7552 of FAM49A) may contribute to NSOC in Chinese populations. MGMT and RHPN2 are associated with NSOC, which is herein demonstrated for the first time.

Deleterious coding variants in multi-case families with non-syndromic cleft lip and/or palate phenotypes

Nonsyndromic Cleft Lip and/or Palate (NSCLP) is regarded as a multifactorial condition in which clefting is an isolated phenotype, distinguished from the largely monogenic, syndromic forms which include clefts among a spectrum of phenotypes. Nonsyndromic clefting has been shown to arise through complex interactions between genetic and environmental factors. However, there is increasing evidence that the broad NSCLP classification may include a proportion of cases showing familial patterns of inheritance and contain highly penetrant deleterious variation in specific genes. Through exome sequencing of multi-case families ascertained in Bogota, Colombia, we identify 28 non-synonymous single nucleotide variants that are considered damaging by at least one predictive score. We discuss the functional impact of candidate variants identified. In one family we find a coding variant in the MSX1 gene which is predicted damaging by multiple scores. This variant is in exon 2, a highly conserved region of the gene. Previous sequencing has suggested that mutations in MSX1 may account for ~2% of NSCLP. Our analysis further supports evidence that a proportion of NSCLP cases arise through monogenic coding mutations, though further work is required to unravel the complex interplay of genetics and environment involved in facial clefting.

Mutation Analysis of the Dimer Forming Domain of the Caspase 8 Gene in Oral Submucous Fibrosis and Squamous Cell Carcinomas

BACKGROUND

Missense and frame-shift mutations within the dimer forming domain of the caspase 8 gene have been identified in several cancers. However, the genetic status of this region in precancerous lesions, like oral submucous fibrosis (OSMF), and well differentiated oral squamous cell carcinomas (OSCCs) in patients from southern region of India is not known, and hence the present study was designed to address this issue.

MATERIALS AND METHODS

Genomic DNA isolated from biopsy tissues of thirty one oral submucous fibrosis and twenty five OSCC samples were subjected to PCR amplification with intronic primers flanking exon 7 of the caspase 8 gene. The PCR amplicons were subsequently subjected to direct sequencing to elucidate the status of mutation.

RESULTS

Sequence analysis identified a frame-shift and a novel missense mutation in two out of twenty five OSCC samples. The frame-shift mutation was due to a two base pair deletion (c.1225_1226delTG), while the missense mutation was due to substitution of wild type cysteine residue with phenylalanine at codon 426 (C426F). The missense mutation, however, was found to be heterozygous as the wild type C426C codon was also present. None of the OSMF samples carried mutations.

CONCLUSIONS

The identification of mutations in OSCC lesions but not OSMF suggests that dimer forming domain mutations in caspase 8 may be limited to malignant lesions. The absence of mutations in OSMF also suggests that the samples analyzed in the present study may not have acquired transforming potential. To the best of our knowledge this is the first study to have explored and identified frame-shift and novel missense mutations in OSCC tissue samples.