PKDCC rs6740960: Facial Shape and Craniofacial Genetics
Single nucleotide polymorphism rs6740960 is an intergenic cis-regulatory variant located at the 2p21 locus near the PKDCC gene. Genome-wide association studies link this variant to normal-range differences in human lower jaw and chin morphology, as well as complex epistatic interactions during craniofacial development. Functional research reveals that it modulates PKDCC expression in cranial chondrocytes, subtly influencing skeletal and cartilage formation.
What each genotype means
Reduced lower jaw prominence
You carry two copies of the derived A allele near the PKDCC gene. In human facial morphology studies, this genotype correlates with higher PKDCC expression in cranial chondrocytes, which statistically associates with a relatively less prominent lower jaw and chin along with midfacial differences. This variant also exhibits epistatic interactions with loci like SLCO2A1 in shaping craniofacial features.
Carried by approximately 25% to 30% of European and South Asian individuals, but present in under 1% of East Asian populations.
Intermediate jaw shape profile
You carry one A allele and one T allele at rs6740960. Research indicates an intermediate regulatory effect on PKDCC expression during cartilage development compared to homozygous genotypes. In population studies, heterozygous individuals exhibit an intermediate facial shape profile involving lower jaw projection and midfacial dimensions.
Found in about 50% of people of European and South Asian ancestries, around 30% to 35% of African ancestry individuals, and roughly 4% of East Asian individuals.
Increased lower jaw prominence
You carry two copies of the ancestral T allele near PKDCC. In craniofacial GWAS and functional studies, this genotype is associated with reduced PKDCC enhancer activity during chondrogenesis, correlating with increased protrusion of the lower jaw and zygomatic regions relative to the midface. This allele has also been studied in connection with genetic susceptibility to non-syndromic cleft lip and palate in European cohorts.
Present in roughly 20% to 25% of European and South Asian individuals, over 60% of African ancestry individuals, and over 95% of East Asian populations.
Chromosomal Location and Regulatory Architecture
The single nucleotide polymorphism rs6740960 is positioned on chromosome 2 within the 2p21 cytogenetic region. It consists of an A/T base substitution situated in a non-coding regulatory segment upstream of the protein kinase domain containing, cytoplasmic (PKDCC) gene. Rather than directly changing the amino acid sequence of a protein, functional genomics experiments have established that rs6740960 sits directly within a distant cis-regulatory enhancer. This enhancer exhibits chromatin marks indicative of cell-type-specific activity, particularly in chondrogenic precursors during embryonic development. Epigenetic profiling indicates that the alternate alleles alter local enhancer acetylation and transcription factor binding efficiency, which in turn modulates the physical looping of DNA required to govern the expression dosage of neighboring target genes, notably PKDCC.
The Biological Role of the PKDCC Gene
The PKDCC gene encodes a secreted extracellular tyrosine-protein kinase that operates within the secretory pathway and extracellular matrix. This kinase plays a central role in vertebrate skeletal biology, endochondral ossification, and the coordination of Hedgehog and growth factor signaling cascades during chondrogenesis. In humans and mammalian models, normal levels of PKDCC are necessary for proper cartilage differentiation and bone elongation. Biallelic loss-of-function pathogenic mutations in PKDCC cause rare, severe syndromic conditions such as rhizomelic skeletal dysplasia, marked by micrognathia and cleft palate. In mouse models, homozygous knockouts exhibit substantial craniofacial malformations, whereas modest reductions in gene dosage produce quantitative, subclinical changes in the proportions of the maxilla and mandible without causing clinical pathology.
Morphological Traits and Evidence Strength
Multiple high-resolution multivariate genome-wide association studies (GWAS) analyzing 3D facial imaging have repeatedly identified rs6740960 as a top lead variant for human facial variation. Specifically, statistical associations highlight significant impacts on the lower face, chin prominence, mandibular projection, and the relative positioning of the zygomatic and midfacial regions. Large cohort studies describe how the T allele subtly alters the balance between jaw protrusion and midface retrusion. Beyond isolated additive effects, researchers have identified epistatic interactions involving this locus and transporters such as SLCO2A1 during craniofacial patterning. Independent studies have also evaluated rs6740960 in the context of non-syndromic cleft lip and palate susceptibility, demonstrating that subtle reductions in chondrocytic PKDCC dosage can shift palatal shelf distance, although it represents only a mild, non-deterministic modifier rather than an isolated cause of disease.
Population Patterns and Evolutionary Context
The allele frequencies of rs6740960 exhibit marked divergence across global populations. Evolutionary geneticists note that the ancestral allele and the derived allele have experienced substantial frequency shifts between European, African, East Asian, and Indigenous American ancestral groups. In European-ancestry cohorts examined in facial morphology GWAS, both the A and T alleles remain common, enabling fine-grained statistical mapping. By contrast, several East Asian cohorts demonstrate pronounced enrichment of one allele. Evolutionary anthropologists hypothesize that such shifts may reflect historical dietary changes influencing masticatory stress and jaw biomechanics, or sexual selection regarding facial contouring, though genetic buffering through secondary compensatory loci also explains why phenotypic consequences differ across ancestral backgrounds.
Practical Interpretation and Limitations
It is essential to understand that rs6740960 represents a common regulatory polymorphism with small, cumulative effects on complex physical traits, rather than a diagnostic clinical mutation. An individual cannot determine their precise jaw shape, chin profile, or facial geometry purely by reading their rs6740960 genotype. Human craniofacial architecture is deeply polygenic, shaped by hundreds of loci acting in concert with developmental timing, nutritional variables, and mechanical factors. Finding this variant in consumer genetic data does not indicate a medical disorder or facial deformity. It simply illustrates the subtle, everyday genetic diversity that makes human facial features unique across individuals and families.
How common is this variant?
Allele frequencies for rs6740960 vary significantly across continental populations, with both alleles maintaining common representation in European cohorts while displaying notable frequency divergence in East Asian and African groups.
Frequently asked questions
Does my rs6740960 genotype dictate the shape of my jaw?
No. While rs6740960 shows statistically robust associations with mandibular dimensions, it is merely one contributor among hundreds of genetic loci. Normal variations in facial shape arise from complex polygenic networks combined with environmental and developmental factors.
Is rs6740960 linked to any genetic disorders?
Severe, rare mutations within the PKDCC gene can cause congenital skeletal dysplasias, but rs6740960 is not one of those damaging mutations. It is a common, benign regulatory variant associated with normal physical traits and weak statistical shifts in orofacial clefting risk.
Can doctors use this variant to diagnose facial abnormalities?
No. Because rs6740960 is very common in the general population and conveys very subtle quantitative shifts in gene expression, it carries no diagnostic or clinical utility for craniofacial evaluation.
How does rs6740960 influence gene activity without changing protein sequence?
The variant is located in a distant enhancer region rather than the protein-coding sequence. It alters local chromatin accessibility and histone acetylation in embryonic cartilage cells, which slightly alters how much PKDCC protein is synthesized during development.
Sources & further reading
Educational information only, last refreshed 9/12/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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