Combining genetic and single-cell expression data reveals cell types and novel candidate genes for orofacial clefting

Non-syndromic cleft lip with/without cleft palate (nsCL/P) is one of the most common birth defects and has a multifactorial etiology. To date, over 45 loci harboring common risk variants have been identified. However, the effector genes at these loci, and the cell types that are affected by risk alleles, remain largely unknown. To address this, we combined genetic data from an nsCL/P genome-wide association study (GWAS) with single-cell RNA sequencing data obtained from the heads of unaffected human embryos. Using the recently developed single-cell disease relevance score (scDRS) approach, we identified two major cell types involved in nsCL/P development, namely the epithelium and the HAND2+ pharyngeal arches (PA). Combining scDRS with co-expression networks and differential gene expression analysis, we prioritized nsCL/P candidate genes, some of which were additionally supported by GWAS data (e.g., CTNND1, PRTG, RPL35A, RAB11FIP1, KRT19). Our results suggest that specific epithelial and PA sub-cell types are involved in nsCL/P development, and harbor a substantial fraction of the genetic risk for nsCL/P.