SUMMARY. African Americans are disproportionately affected by chronic and end stage renal disease (ESRD);
while 35% of patients on dialysis are African American, only 13.2% of the U.S. population is African American.
A major factor contributing to this disparity are genetic variations in apolipoprotein L1 (APOL1). APOL1 is a
plasma protein protective against ‘African sleeping sickness’ caused by the parasite Trypanosoma brucei. There
are three main allelic variants of APOL1: G0 (wild-type), G1, and G2. The G1 and G2 APOL1 alleles (i.e., renal
risk alleles) impart resistance to sleeping sickness, while the G0 allele enables parasite survival and infection.
For this reason, the G1 and G2 alleles are highly prevalent in individuals with African ancestry. The G1 and G2
variants of APOL1 are also present at relatively high frequencies among African Americans, with approximately
35% of the African American population having at least one G1 or G2 allele. Despite providing an advantage in
survival from African trypanosomiasis, these genotypic variants predispose individuals to develop severe,
irreparable kidney disease. People with two risk alleles, i.e., who are homozygous for either the G1 or G2 alleles
or are doubly heterozygous for these alleles (G1/G2), have an APOL1 ‘risk genotype’ and are at elevated risk
for developing focal segmental glomerulosclerosis (FSGS), which leads to progressive scarring and loss of
function of glomeruli. Moreover, the risk genotype is associated with reduced allograft longevity in kidneys
transplanted from donors with two risk alleles. More recently, it has been found that other glomerulopathies linked
to viral infections, including HIV and SARS-CoV-2, are exacerbated by having the APOL1 risk genotype. Given
that approximately 13% of African Americans have a genotype with two risk alleles, APOL1-linked kidney disease
represents a potentially massive, yet still underappreciated, public health issue. The available methods for
detecting pathological APOL1 variants, including gene sequencing and TaqMan, are relatively expensive and
require specialized equipment and skills. Recently, CRISPR/Cas-based methods of detecting specific nucleic
acid sequences have been developed. These methods are both simple and inexpensive and therefore offer
significant advantages to conventional genotyping methods. In this Phase I application, we propose to develop
a proof-of-concept CRISPR/Cas12a-based genotyping assay to detect the G0, G1, and G2 variants of ApoL1.
Once developed and optimized, this assay will lead to a suite of reagents and techniques to expand access to
simple and affordable ApoL1 genotyping that is less reliant on specialized equipment. Two novel therapeutic
agents for treatment of APOL1-mediated kidney disease are currently in clinical trials, highlighting the urgency
to develop better diagnostic tools that can identify individuals who could benefit from these treatments.