Project Summary Familial hypercholesterolemia (FH) is a heritable disorder affecting 1.3 million individuals in the United States. Eighty percent of people with FH have not yet been diagnosed, and this gap is even more robust for people from minoritized populations, including Black or African American people. Family cascade screening is an evidence- based practice that includes contacting and screening family members of people diagnosed with FH, but it is rarely implemented representing a care gap in all populations, and particularly in Black or African American people. The proposed work aims to use multi-methods to elucidate factors related to implementation of cascade screening in Black or African American people in pursuit of identifying targets for future strategies to mitigate this inequity. The parent grant supporting this Diversity Supplement is a hybrid effectiveness-implementation type III randomized controlled trial testing the comparative effectiveness of two strategies to implement family cascade screening with individuals with FH. Closing inequities in minoritized groups including African American or Black people, Asian or Asian American people, and women across racial groups is a focus of the parent grant, specifically by exploring equitable reach by sub-population, and in conducting interviews and centering diverse voices. Under the primary mentorship of Dr. Rinad Beidas, the candidate, Ms. Chynna Mills, will extend the aims of the parent grant using an established framework for health behavior to examine understudied multi-level factors using multi-methods that may be related to reach of family cascade screening for Black or African American people. In Aim 1, Ms. Mills will examine the relationship between a set of theoretically informed multi- level candidate variables and the primary outcome (reach) in 100 Black or African American probands. In Aim 2, Ms. Mills will explore mechanistic pathways of cascade screening reach via qualitative interviews. Ms. Mills has prior experience examining multi-level factors impacting Black or African American people’s participation in health interventions and is committed to a career as an independent investigator focused on improving implementation of and engagement with evidence-based practices for Black or African American populations. This Diversity Supplement will support the candidate’s development of an independent program of research through mentored training. Results will offer insights on how to close inequitable gaps in implementation of cascade screening with Black or African American populations and has the potential to lessen disparities in reach of family cascade screening for Black or African American people with FH and other heritable genetic disorders.