Evaluating SKI as a candidate gene for non-syndromic cleft lip with or without cleft palate

Genome Analysis Using Whole-Exome Sequencing of Non-Syndromic Cleft Lip and/or Palate from Malagasy Trios Identifies Variants Associated with Cilium-Related Pathways and Asian Genetic Ancestry

Background: Orofacial clefts (OFCs) are common congenital disabilities that can occur as isolated non-syndromic events or as part of Mendelian syndromes. OFC risk factors vary due to differences in regional environmental exposures, genetic variants, and ethnicities. In recent years, significant progress has been made in understanding OFCs, due to advances in sequencing and genotyping technologies. Despite these advances, very little is known about the genetic interplay in the Malagasy population. Methods: Here, we performed high-resolution whole-exome sequencing (WES) on non-syndromic cleft lip with or without palate (nCL/P) trios in the Malagasy population (78 individuals from 26 families (trios)). To integrate the impact of genetic ancestry admixture, we computed both global and local ancestries. Results: Participants demonstrated a high percentage of both African and Asian admixture. We identified damaging variants in primary cilium-mediated pathway genes WNT5B (one family), GPC4 (one family), co-occurrence in MSX1 (five families), WDR11 (one family), and tubulin stabilizer SEPTIN9 (one family). Furthermore, we identified an autosomal homozygous damaging variant in PHGDH (one family) gene that may impact metabiotic activity. Lastly, all variants were predicted to reside on local Asian genetic ancestry admixed alleles. Conclusion: Our results from examining the Malagasy genome provide limited support for the hypothesis that germline variants in primary cilia may be risk factors for nCL/P, and outline the importance of integrating local ancestry components better to understand the multi-ethnic impact on nCL/P.

Non-syndromic Cleft Lip and Palate Polymorphisms Affect Normal Lip Morphology

Non-syndromic cleft lip with or without palate (NSCL/P) is a frequent malformation of the facial region. Genetic variants (SNPs) within nineteen loci have been previously associated with NSCL/P in GWAS studies of European individuals. These common variant SNPs may have subtler effects on the morphology of the lip and face in unaffected individuals. Several studies have investigated the genetic influences on facial morphology using land-marking methods, but these landmarks are sparse in the lip region. The aim of this study is to assess for associations between the nineteen NSCL/P SNPs and normal lip phenotypes, using a detailed categorical scale. Three-dimensional laser scanned facial images were obtained of 4,747 subjects recruited from the Avon Longitudinal Study of Parents and Children (ALSPAC) and genetic data was available for 3,643 of them. A polygenetic risk score (PRS) combining the nineteen NSCL/P SNPs was associated with V-shaped Cupid's bow (P = 3 × 10⁻⁴) and narrow philtrum (P = 2 × 10⁻⁴) phenotypes. Analysis of individual SNPs found strong evidence for association between rs227731 and skeletal II pattern (P = 5 × 10⁻⁶). This study finds that known NSCL/P SNPs affect lip phenotypes in the general population, and an increased PRS is associated with narrow philtrum and V-shaped Cupid's bow. However, the difference in NSCL/P PRS between people with and without certain lip features is unlikely to be great enough to serve as a useful marker of NSCL/P risk.

Compound heterozygosity of low-frequency promoter deletions and rare loss-of-function mutations in TXNL4A causes Burn-McKeown syndrome

Mutations in components of the major spliceosome have been described in disorders with craniofacial anomalies, e.g., Nager syndrome and mandibulofacial dysostosis type Guion-Almeida. The U5 spliceosomal complex of eight highly conserved proteins is critical for pre-mRNA splicing. We identified biallelic mutations in TXNL4A, a member of this complex, in individuals with Burn-McKeown syndrome (BMKS). This rare condition is characterized by bilateral choanal atresia, hearing loss, cleft lip and/or palate, and other craniofacial dysmorphisms. Mutations were found in 9 of 11 affected families. In 8 families, affected individuals carried a rare loss-of-function mutation (nonsense, frameshift, or microdeletion) on one allele and a low-frequency 34 bp deletion (allele frequency 0.76%) in the core promoter region on the other allele. In a single highly consanguineous family, formerly diagnosed as oculo-oto-facial dysplasia, the four affected individuals were homozygous for a 34 bp promoter deletion, which differed from the promoter deletion in the other families. Reporter gene and in vivo assays showed that the promoter deletions led to reduced expression of TXNL4A. Depletion of TXNL4A (Dib1) in yeast demonstrated reduced assembly of the tri-snRNP complex. Our results indicate that BMKS is an autosomal-recessive condition, which is frequently caused by compound heterozygosity of low-frequency promoter deletions in combination with very rare loss-of-function mutations.