Apolipoprotein L1 and kidney transplantation

Taking a "Care Pathway/Whole Systems" Approach to Equality Diversity Inclusion (EDI) in Organ Donation and Transplantation in Relation to the Needs of "Ethnic/Racial/Migrant" Minority Communities: A Statement and a Call for Action

International evidence shows variation in organ donation and transplantation (ODT) based upon a range of patient characteristics. What is less well understood is the impact of patient "ethnicity/race/immigration background," as these terms are defined and intended differently across countries. We also know that these characteristics do not operate in isolation but intersect with a range of factors. In this paper, we propose a framework that seeks to clarify the definition of the key terms "ethnicity/race/migrant" and to review how these communities are operationalized across European studies about inequities in ODT. Further, patients and the public wish to see Equality Diversity Inclusion (EDI) approaches in their everyday lives, not just in relation to ODT. We propose a 'care pathway/whole-systems' approach to ODT encompassing culturally competent public health interventions for a) the prevention and management of chronic diseases, b) improvements in public engagement for the promotion of the culture of ODT and enhancements in end-of-life care, through to c) enhanced likelihood of successful transplant among migrant/ethnic minority communities. Our framework recognizes that if we truly wish to take an EDI approach to ODT, we need to adopt a more social, human and holistic approach to examining questions around patient ethnicity.

Genetic evaluation of living kidney donor candidates: A review and recommendations for best practices

The growing accessibility and falling costs of genetic sequencing techniques has expanded the utilization of genetic testing in clinical practice. For living kidney donation, genetic evaluation has been increasingly used to identify genetic kidney disease in potential candidates, especially in those of younger ages. However, genetic testing on asymptomatic living kidney donors remains fraught with many challenges and uncertainties. Not all transplant practitioners are aware of the limitations of genetic testing, are comfortable with selecting testing methods, comprehending test results, or providing counsel, and many do not have access to a renal genetic counselor or a clinical geneticist. Although genetic testing can be a valuable tool in living kidney donor evaluation, its overall benefit in donor evaluation has not been demonstrated and it can also lead to confusion, inappropriate donor exclusion, or misleading reassurance. Until more published data become available, this practice resource should provide guidance for centers and transplant practitioners on the responsible use of genetic testing in the evaluation of living kidney donor candidates.

The evolving story of apolipoprotein L1 nephropathy: the end of the beginning

Genetic coding variants in APOL1, which encodes apolipoprotein L1 (APOL1), were identified in 2010 and are relatively common among individuals of sub-Saharan African ancestry. Approximately 13% of African Americans carry two APOL1 risk alleles. These variants, termed G1 and G2, are a frequent cause of kidney disease — termed APOL1 nephropathy — that typically manifests as focal segmental glomerulosclerosis and the clinical syndrome of hypertension and arterionephrosclerosis. Cell culture studies suggest that APOL1 variants cause cell dysfunction through several processes, including alterations in cation channel activity, inflammasome activation, increased endoplasmic reticulum stress, activation of protein kinase R, mitochondrial dysfunction and disruption of APOL1 ubiquitinylation. Risk of APOL1 nephropathy is mostly confined to individuals with two APOL1 risk variants. However, only a minority of individuals with two APOL1 risk alleles develop kidney disease, suggesting the need for a ‘second hit’. The best recognized factor responsible for this ‘second hit’ is a chronic viral infection, particularly HIV-1, resulting in interferon-mediated activation of the APOL1 promoter, although most individuals with APOL1 nephropathy do not have an obvious cofactor. Current therapies for APOL1 nephropathies are not adequate to halt progression of chronic kidney disease, and new targeted molecular therapies are in clinical trials.

This Review summarizes current understanding of the role of APOL1 variants in kidney disease. The authors discuss the genetics, protein structure and biological functions of APOL1 variants and provide an overview of promising therapeutic strategies.

In contrast to other APOL family members, which are primarily intracellular, APOL1 contains a unique secretory signal peptide, resulting in its secretion into plasma.

APOL1 renal risk alleles provide protection from African human trypanosomiasis but are a risk factor for progressive kidney disease in those carrying two risk alleles.

APOL1 risk allele frequency is ~35% in the African American population in the United States, with ~13% of individuals having two risk alleles; the highest allele frequencies are found in West African populations and their descendants.

Cell and mouse models implicate endolysosomal and mitochondrial dysfunction, altered ion channel activity, altered autophagy, and activation of protein kinase R in the pathogenesis of APOL1-associated kidney disease; however, the relevance of these injury pathways to human disease has not been resolved.

APOL1 kidney disease tends to be progressive, and current standard therapies are generally ineffective; targeted therapeutic strategies hold the most promise.

Podocytopathies

Podocytopathies are kidney diseases in which direct or indirect podocyte injury drives proteinuria or nephrotic syndrome. In children and young adults, genetic variants in >50 podocyte-expressed genes, syndromal non-podocyte-specific genes and phenocopies with other underlying genetic abnormalities cause podocytopathies associated with steroid-resistant nephrotic syndrome or severe proteinuria. A variety of genetic variants likely contribute to disease development. Among genes with non-Mendelian inheritance, variants in APOL1 have the largest effect size. In addition to genetic variants, environmental triggers such as immune-related, infection-related, toxic and haemodynamic factors and obesity are also important causes of podocyte injury and frequently combine to cause various degrees of proteinuria in children and adults. Typical manifestations on kidney biopsy are minimal change lesions and focal segmental glomerulosclerosis lesions. Standard treatment for primary podocytopathies manifesting with focal segmental glomerulosclerosis lesions includes glucocorticoids and other immunosuppressive drugs; individuals not responding with a resolution of proteinuria have a poor renal prognosis. Renin-angiotensin system antagonists help to control proteinuria and slow the progression of fibrosis. Symptomatic management may include the use of diuretics, statins, infection prophylaxis and anticoagulation. This Primer discusses a shift in paradigm from patient stratification based on kidney biopsy findings towards personalized management based on clinical, morphological and genetic data as well as pathophysiological understanding.