Chebib, Fouad T.

Importance Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive development of kidney cysts and is the most common inherited kidney disorder worldwide. ADPKD accounts for 5% to 10% of kidney failure in the US and Europe, and its prevalence in the US is 9.3 per 10 000 individuals. Observations ADPKD is typically diagnosed in individuals aged 27 to 42 years and is primarily caused by pathogenic variants in the PKD1 (78%) or PKD2 (15%) genes. Most persons with ADPKD have an affected parent, but de novo disease is suggested in 10% to 25% of families. More than 90% of patients older than 35 years have hepatic cysts, which may cause abdominal discomfort and occasionally require medical or surgical intervention. Hypertension affects 70% to 80% of patients with ADPKD, and approximately 9% to 14% develop intracranial aneurysms, which have a rupture rate of 0.57 per 1000 patient-years. Approximately 50% of individuals with ADPKD require kidney replacement therapy by 62 years of age. The severity of kidney disease can be quantified using the Mayo Imaging Classification (MIC), which stratifies patients based on total kidney volume adjusted for height and age and ranges from 1A to 1E. Patients with MIC 1C to MIC 1E have larger kidneys because of more rapid growth (6%-10% per year) compared with those with MIC 1A and 1B (1%-5% per year) and have earlier progression to kidney replacement therapy, which occurs at a mean age of 58.4 years for MIC 1C, 52.5 years for MIC 1D, and 43.4 years for MIC 1E. Optimal management of ADPKD includes systolic blood pressure lower than 120 mm Hg for most patients, but lower than 110/75 mm Hg for patients with MIC 1C to 1E who have an estimated glomerular filtration rate (eGFR) greater than 60 mL/min/1.73 m 2 and are younger than 50 years, dietary sodium restriction (<2000 mg/d), weight management, and adequate hydration (>2.5 L daily). The vasopressin type 2 receptor antagonist tolvaptan reduces the annual rate of eGFR decline by 0.98 to 1.27 mL/min/1.73 m 2 and is indicated for patients with MIC 1C to 1E or an eGFR decline greater than 3 mL/min/1.73 m 2 per year to slow disease progression and delay the onset of kidney failure. Conclusion ADPKD is the most common genetic kidney disease worldwide and is characterized by progressive development of kidney cysts. Patients typically have hypertension and liver cysts, and 9% to 14% develop intracranial aneurysms. First-line treatment includes blood pressure control, dietary and weight management, and adequate hydration. Tolvaptan reduces the rate of eGFR decline for those at high risk of rapid progression to kidney failure.

Key Points Loss-of-function ALG8 and ALG9 variants were enriched in polycystic kidney/liver groups and International Classification of Diseases–coded cystic individuals in population cohorts. The ALG8 and ALG9 kidney phenotypes were usually mild to moderate, and lower eGFR or kidney failure was rare. ALG8 pathogenic variants sometimes resulted in severe polycystic liver disease. Background Autosomal dominant polycystic kidney disease (ADPKD) is a common, inherited nephropathy often resulting in kidney failure. It is genetically heterogeneous; along with the major genes, PKD1 and PKD2 , at least eight others have been suggested. ALG8 pathogenic variants have been associated with autosomal dominant polycystic liver disease and implicated in ADPKD, while ALG9 has been suggested as an ADPKD gene, but details of the phenotypes and penetrance are unclear. Methods We screened >3900 families with cystic kidneys and/or livers using global approaches to detect ALG8 or ALG9 pathogenic variants. In addition, population cohorts with sequence data (Genomics England 100K Genomics Project, UK Biobank, and Mayo Clinic Biobank [MCBB]) were screened for ALG8 / ALG9 pathogenic variants. Results Multicenter screening of individuals with polycystic kidney and/or liver disease identified 51 (1.3%) ALG8 (7 multiplex) and 23 (0.6%) ALG9 (5 multiplex) families—frequencies that were approximately 10× and approximately 24× greater than nonpolycystic kidney disease controls. Analysis of individuals with polycystic kidney disease phenotypes in 100K Genomics Project, UK Biobank, and MCBB identified nine ALG8 (0.39%) and nine ALG9 (0.39%) families, an enriched frequency over controls. Two individuals had PKD1 and ALG8 pathogenic changes. Eighty-nine percent of individuals with ALG8 mutations with imaging in the entire MCBB had kidney cysts (50%, >10 cysts), with greater median kidney and liver cyst numbers than controls. For ALG9, 78% had kidney cysts (27%, >10 cysts). Individuals with ALG8 mutations typically had mild cystic kidneys with limited enlargement. Liver cysts were common (71%), with enlarged livers (>2L) found in 11 of 62 patients, although surgical intervention was rare. The ALG9 kidney phenotype was also of mild cystic kidneys, but enlarged livers were rare; for both genes, CKD or kidney failure were rare. Conclusions ALG8 and ALG9 are defined as cystic kidney/liver genes but with limited penetrance for lower eGFR.

The Autosomal Dominant Polycystic Kidney Disease (ADPKD) Centers of Excellence (COE) Program, launched by the Polycystic Kidney Disease Foundation in 2022, aims to bridge the gap in specialized care for individuals with ADPKD. This program seeks to enhance the availability of specialized clinicians and simplify the process for patients seeking expert care. It is founded on three pillars: improving care for all individuals with ADPKD, educating and empowering the community, and advancing polycystic kidney disease research. The program draws inspiration from successful models in other diseases, such as cystic fibrosis and muscular dystrophy, which have demonstrated the effectiveness of standardized care centers in improving patient outcomes. Patient and clinician stakeholder interviews have identified key areas where a national program could make a significant effect, including the need for a core care team with defined referral processes, mentorship and shared care models, patient navigation services, and education around expert consensus and care guidelines. The program introduces two designations to accommodate diverse care settings and enhance patient access to specialists: COE and Partner Clinic. The Partner Clinic designation ensures that patients in smaller community practices have access to specialized care through mentorship and guidance from experts at COE. The program also emphasizes the importance of specialized services, especially in underserved communities experiencing health disparities, to manage the complexities of ADPKD care. Patient focus groups have highlighted the need for care navigation services, centralized sources of knowledge, and access to local care. The program aims to address these needs by providing a structured framework for care coordination, enhancing patient self-advocacy, and improving overall outcomes for individuals with ADPKD. Key Points The Autosomal Dominant Polycystic Kidney Disease Centers of Excellence Program aims to improve specialized care for autosomal dominant polycystic kidney disease patients. It introduces two designations to accommodate diverse care settings and enhance patient access to specialists: Center of Excellence and Partner Clinic. The program draws inspiration from successful models in other diseases, such as cystic fibrosis and muscular dystrophy, which have demonstrated the effectiveness of standardized care centers in improving patient outcomes. Key needs and programmatic goals identified through patient and clinician stakeholder interviews include establishing a core care team with defined referral processes, implementing mentorship and shared care models, providing patient navigation services, and offering education on expert consensus and care guidelines.