Shared genetic risk between major orofacial cleft phenotypes in an African population

Nonsyndromic orofacial clefts (NSOFCs) represent a large proportion (70%–80%) of all OFCs. They can be broadly categorized into nonsyndromic cleft lip with or without cleft palate (NSCL/P) and nonsyndromic cleft palate only (NSCPO). Although NSCL/P and NSCPO are considered etiologically distinct, recent evidence suggests the presence of shared genetic risks. Thus, we investigated the genetic overlap between NSCL/P and NSCPO using African genome-wide association study (GWAS) data on NSOFCs. These data consist of 814 NSCL/P, 205 NSCPO cases, and 2159 unrelated controls. We generated common single-nucleotide variants (SNVs) association summary statistics separately for each phenotype (NSCL/P and NSCPO) under an additive genetic model. Subsequently, we employed the pleiotropic analysis under the composite null (PLACO) method to test for genetic overlap. Our analysis identified two loci with genome-wide significance (rs181737795 [p = 2.58E−08] and rs2221169 [p = 4.5E−08]) and one locus with marginal significance (rs187523265 [p = 5.22E−08]). Using mouse transcriptomics data and information from genetic phenotype databases, we identified MDN1, MAP3k7, KMT2A, ARCN1, and VADC2 as top candidate genes for the associated SNVs. These findings enhance our understanding of genetic variants associated with NSOFCs and identify potential candidate genes for further exploration.</p

Clinically actionable secondary findings in 130 triads from sub-Saharan African families with non-syndromic orofacial clefts

Abstract Introduction The frequency and implications of secondary findings (SFs) from genomic testing data have been extensively researched. However, little is known about the frequency or reporting of SFs in Africans, who are underrepresented in large‐scale population genomic studies. The availability of data from the first whole‐genome sequencing for orofacial clefts in an African population motivated this investigation. Methods In total, 130 case‐parent trios were analyzed for SFs within the ACMG SFv.3.0 list genes. Additionally, we filtered for four more genes (HBB, HSD32B, G6PD and ACADM). Results We identified 246 unique variants in 55 genes; five variants in four genes were classified as pathogenic or likely pathogenic (P/LP). The P/LP variants were seen in 2.3% (9/390) of the subjects, a frequency higher than ~1% reported for diverse ethnicities. On the ACMG list, pathogenic variants were observed in PRKAG (p. Glu183Lys). Variants in the PALB2 (p. Glu159Ter), RYR1 (p. Arg2163Leu) and LDLR (p. Asn564Ser) genes were predicted to be LP. Conclusion This study provides information on the frequency and pathogenicity of SFs in an African cohort. Early risk detection will help reduce disease burden and contribute to efforts to increase knowledge of the distribution and impact of actionable genomic variants in diverse populations

Non-random distribution of deleterious mutations in the DNA and protein-binding domains of IRF6 are associated with Van Der Woude syndrome

Background: The development of the face occurs during the early days of intrauterine life by the formation of facial processes from the first Pharyngeal arch. Derangement in these well-organized fusion events results in Orofacial clefts (OFC). Van der Woude syndrome (VWS) is one of the most common causes of syndromic cleft lip and/or palate accounting for 2% of all cases. Mutations in the IRF6 gene account for 70% of cases with the majority of these mutations located in the DNA-binding (exon 3, 4) or protein-binding domains (exon 7-9). The current study was designed to update the list of IRF6 variants reported for VWS by compiling all the published mutations from 2013 to date as well as including the previously unreported VWS cases from Africa and Puerto Rico.Methods: We used PubMed with the search terms; "Van der Woude syndrome," "Popliteal pterygium syndrome," "IRF6," and "Orofacial cleft" to identify eligible studies. We compiled the CADD score for all the mutations to determine the percentage of deleterious variants.Results: Twenty-one new mutations were identified from nine papers. The majority of these mutations were in exon 4. Mutations in exon 3 and 4 had CADD scores between 20 and 30 and mutations in exon 7-9 had CADD scores between 30 and 40. The presence of higher CADD scores in the protein-binding domain (exon 7-9) further confirms the crucial role played by this domain in the function of IRF6. In the new cases, we identified five IRF6 mutations, three novel missense mutations (p.Phe36Tyr, p.Lys109Thr, and p.Gln438Leu), and two previously reported nonsense mutations (p.Ser424*and p.Arg250*).Conclusion: Mutations in the protein and DNA-binding domains of IRF6 ranked among the top 0.1% and 1% most deleterious genetic mutations, respectively. Overall, these findings expand the range of VWS mutations and are important for diagnostic and counseling purposes.</p

Novel IRF6 variant in orofacial cleft patients from Durban, South Africa

Abstract Background To date, there are over 320 variants identified in the IRF6 gene that cause Van der Woude syndrome or popliteal pterygium syndrome. We sequenced this gene in a South African orofacial cleft cohort to identify the causal IRF6 variants in our population. Method Saliva samples from 100 patients with syndromic and non‐syndromic CL ± P were collected. Patients were recruited from the cleft clinics at two public, tertiary hospitals in Durban, South Africa (SA), namely Inkosi Albert Luthuli Central Hospital (IALCH) and KwaZulu‐Natal Children's Hospital (KZNCH). We prospectively sequenced the exons of IRF6 in 100 orofacial cleft cases, and where possible, we also sequenced the parents of the individuals to determine the segregation pattern. Results Two variants were identified; one novel (p.Cys114Tyr) and one known (p.Arg84His) missense variant in IRF6 gene were identified. The patient with the p.Cys114Tyr variant was non‐syndromic with no clinical VWS phenotype expected of individuals with IRF6 coding variants, and the patient with the p.Arg84His had phenotypic features of popliteal pterygium syndrome. The p.Arg84His variant segregated in the family, with the father also being affected. Conclusions This study provides evidence that IRF6 variants are found in the South African population. Genetic counselling is essential for affected families, particularly in the absence of a known clinical phenotype since it helps with the plans for future pregnancies

Whole-genome sequencing reveals de-novo mutations associated with nonsyndromic cleft lip/palate

The majority (85%) of nonsyndromic cleft lip with or without cleft palate (nsCL/P) cases occur sporadically, suggesting a role for de novo mutations (DNMs) in the etiology of nsCL/P. To identify high impact protein-altering DNMs that contribute to the risk of nsCL/P, we conducted whole-genome sequencing (WGS) analyses in 130 African case-parent trios (affected probands and unaffected parents). We identified 162 high confidence protein-altering DNMs some of which are based on available evidence, contribute to the risk of nsCL/P. These include novel protein-truncating DNMs in the ACTL6A, ARHGAP10, MINK1, TMEM5 and TTN genes; as well as missense variants in ACAN, DHRS3, DLX6, EPHB2, FKBP10, KMT2D, RECQL4, SEMA3C, SEMA4D, SHH, TP63, and TULP4. Many of these protein-altering DNMs were predicted to be pathogenic. Analysis using mouse transcriptomics data showed that some of these genes are expressed during the development of primary and secondary palate. Gene-set enrichment analysis of the protein-altering DNMs identified palatal development and neural crest migration among the few processes that were significantly enriched. These processes are directly involved in the etiopathogenesis of clefting. The analysis of the coding sequence in the WGS data provides more evidence of the opportunity for novel findings in the African genome