PROJECT SUMMARY Orofacial clefts (OFCs) are one of the most common birth defects, affecting approximately 1 in 700 births globally, and are phenotypically variable, including clefts of the lip (CL), palate (CP), and lip and palate (CLP). While most cases of OFCs are sporadic, recurrence risk ratios of OFCs in relatives of affected individuals are substantial, highlighting a strong genetic component to this group of disorders. Nevertheless, despite considerable evidence that OFCs are heritable, a variety of genetic studies of OFCs over the past century have yet to identify genetic factors that explain the majority of this heritability. One possible explanation is that some genetic variants only increase risk for certain subtypes of OFCs and thus these variants have been missed in standard analyses that combine subtypes together to bolster sample size ostensibly for improved power in gene mapping. The overall hypothesis of this proposal is that this high recurrence risk for subtypes of OFCs in families is caused by inheritance of both rare and common subtype-specific genetic risk variants, many of which are still unknown. In order to better investigate both rare and common genetic variants that cause OFCs, we will use family-based genetic approaches since they are powerful methods to identify potentially causal, segregating variants. Additionally, this proposal is unique in that the primary goal is not just to identify and potentially test these variants functionally, but to understand how these risk variants segregate in families and interact with known environmental risk factors, leading to a better understanding of subtype-specific OFC risk. The central hypothesis of this proposal will be tested in two independent aims: first, testing rare genetic variant transmission in families with OFCs, leveraging both whole-genome sequencing data and genotyping data, and second, developing a subtype-specific polygenic risk score (PRS) and testing the genetic risk in affected and unaffected family members. I have assembled a mentoring team to provide the necessary training and support to accomplish the proposed research: sponsors Dr. Elizabeth Leslie and Dr. Michael Epstein and collaborators Dr. Mary Marazita, Dr. Terri Beaty, and Dr. Robert Cornell. The proposed project and training plan are tailored to provide training in statistical genetics, sequencing, and family-based analytic methods. Learning these new methods and technologies in genetics will add to my existing skills in environmental epigenetics and will facilitate my growth into an independent genetic epidemiologist.