Combining genotype with height-adjusted kidney length predicts rapid progression of ADPKD.

INTRODUCTION: Our main objective was to identify baseline prognostic factors predictive of rapid disease progression in a large unselected clinical autosomal dominant polycystic kidney disease (ADPKD) cohort. METHODS: A cross-sectional analysis was performed in 618 consecutive ADPKD patients assessed and followed-up for over a decade. A total of 123 patients (19.9%) had reached kidney failure by the study date. Data were available for the following: baseline eGFR (n = 501), genotype (n = 549), baseline ultrasound mean kidney length (MKL, n = 424) and height-adjusted baseline MKL (HtMKL, n = 377). Rapid disease progression was defined as an annualized eGFR decline (∆eGFR) of >2.5 mL/min/year by linear regression over 5 years (n = 158). Patients were further divided into slow, rapid and very rapid ∆eGFR classes for analysis. Genotyped patients were classified into several categories: PKD1 (T, truncating; or NT, non-truncating), PKD2, other genes (non-PKD1 or -PKD2), no mutation detected or variants of uncertain significance. RESULTS: A PKD1-T genotype had the strongest influence on the probability of reduced baseline kidney function by age. A multivariate logistic regression model identified PKD1-T genotype and HtMKL (>9.5 cm/m) as independent predictors for rapid disease progression. The combination of both factors increased the positive predictive value for rapid disease progression over age 40 years and of reaching kidney failure by age 60 years to 100%. Exploratory analysis in a subgroup with available total kidney volumes showed higher positive predictive value (100% vs 80%) and negative predictive value (42% vs 33%) in predicting rapid disease progression compared with the Mayo Imaging Classification (1C-E). CONCLUSION: Real-world longitudinal data confirm the importance of genotype and kidney length as independent variables determining ∆eGFR. Individuals with the highest risk of rapid disease progression can be positively selected for treatment based on this combination.

Modeling of full-length Piezo1 suggests importance of the proximal N-terminus for dome structure.

Piezo1 forms a mechanically activated calcium-permeable nonselective cation channel that is functionally important in many cell types. Structural data exist for C-terminal regions, but we lack information about N-terminal regions and how the entire channel interacts with the lipid bilayer. Here, we use computational approaches to predict the three-dimensional structure of the full-length Piezo1 and simulate it in an asymmetric membrane. A number of novel insights are suggested by the model: 1) Piezo1 creates a trilobed dome in the membrane that extends beyond the radius of the protein, 2) Piezo1 changes the lipid environment in its vicinity via preferential interactions with cholesterol and phosphatidylinositol 4,5-bisphosphate (PIP2) molecules, and 3) cholesterol changes the depth of the dome and PIP2 binding preference. In vitro alteration of cholesterol concentration inhibits Piezo1 activity in a manner complementing some of our computational findings. The data suggest the importance of N-terminal regions of Piezo1 for dome structure and membrane cholesterol and PIP2 interactions.

Biallelic inheritance of hypomorphic PKD1 variants is highly prevalent in very early onset polycystic kidney disease.

PURPOSE: To investigate the prevalence of biallelic PKD1 and PKD2 variants underlying very early onset (VEO) polycystic kidney disease (PKD) in a large international pediatric cohort referred for clinical indications over a 10-year period (2010-2020). METHODS: All samples were tested by Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA) of PKD1 and PKD2 genes and/or a next-generation sequencing panel of 15 additional cystic genes including PKHD1 and HNF1B. Two patients underwent exome or genome sequencing. RESULTS: Likely causative PKD1 or PKD2 variants were detected in 30 infants with PKD-VEO, 16 of whom presented in utero. Twenty-one of 30 (70%) had two variants with biallelic in trans inheritance confirmed in 16/21, 1 infant had biallelic PKD2 variants, and 2 infants had digenic PKD1/PKD2 variants. There was no known family history of ADPKD in 13 families (43%) and a de novo pathogenic variant was confirmed in 6 families (23%). CONCLUSION: We report a high prevalence of hypomorphic PKD1 variants and likely biallelic disease in infants presenting with PKD-VEO with major implications for reproductive counseling. The diagnostic interpretation and reporting of these variants however remains challenging using current American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) and Association of Clinical Genetic Science (ACGS) variant classification guidelines in PKD-VEO and other diseases affected by similar variants with incomplete penetrance.

Renal albumin excretion in healthy young adults and its association with mortality risk in the US population.

BACKGROUND: Current classification systems do not specify a healthy normal range for urinary albumin excretion. Occult microvascular disease induced by a Western lifestyle may mean that normal values for apparently healthy adults exceed optimal levels defined by mortality risk. METHODS: Using a national population sample [the US Third National Health and Nutrition Examination Survey (NHANES III) cohort; n = 11 887], the distributions of albumin:creatinine ratio (ACR) and fractional excretion of albumin (FEalb) were studied in healthy young adults [ages 20-40 years, without cardiovascular disease (CVD) or risk factors]. The threshold for mortality risk prediction in the whole adult population sample was then studied across ACR/FEalb categories corresponding to quartiles for healthy young adults. RESULTS: ACR quartiles for healthy young adults were 2.7, 4.2 and 5.9 mg/g in men and 3.8, 6.2 and 9.8 mg/g in women. Increases in ACR below the medians for healthy young adults were not associated with increased mortality or with cardiovascular risk factors when tested in the whole adult population. Increases above this threshold were independently associated with mortality risk [hazard ratio 1.2 (95% confidence interval 1.1-1.4) and 1.8 (1.6-2.0) for Quartiles 3 and 4, respectively]. The prevalence of an optimal ACR below the mortality risk threshold was <25% in the setting of diabetes, hypertension, age >70 years or CVD. Using FEalb to define quartiles of albuminuria gave the same findings. CONCLUSION: Based on mortality risk in the whole adult population, there is an optimal range of albumin excretion (ACR < 6 mg/g and 4 mg/g for women and men, respectively). However, only half of even apparently healthy young US adults fall within this range.

Clinical practice guideline monitoring children and young people with, or at risk of developing autosomal dominant polycystic kidney disease (ADPKD).

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is thought to affect about 1 in 1000 people in the UK. ADPKD causes a progressive decline in kidney function, with kidney failure tending to occur in middle age. Children and young people with ADPKD may not have any symptoms. However they may have high blood pressure, which may accelerate progression to later stages of chronic kidney disease.There is uncertainty and variation in how health professionals manage children and young people with confirmed or a family history of ADPKD, because of a lack of evidence. For example, health professionals may be unsure about when to test children's blood pressure and how often to monitor it in the hospital clinic or at the GP. They may have different approaches in recommending scanning or genetic testing for ADPKD in childhood, with some recommending waiting until the young person is mature enough to make this decision his or herself.This guideline is intended to help families affected by ADPKD by making sure that: health professionals with specialist knowledge in ADPKD offer you information on inheritance and potential benefits and harms of testing for ADPKD. the decision to test and the method of testing for ADPKD in children and young people is shared between you or your family and the health professionals blood pressure assessment is undertaken regularly in children and young people at risk of developing ADPKD.

Maternal inheritance of a promoter variant in the imprinted PHLDA2 gene significantly increases birth weight.

Birth weight is an important indicator of both perinatal and adult health, but little is known about the genetic factors contributing to its variability. Intrauterine growth restriction is a leading cause of perinatal morbidity and mortality and is also associated with adult disease. A significant correlation has been reported between lower birth weight and increased expression of the maternal PHLDA2 allele in term placenta (the normal imprinting pattern was maintained). However, a mechanism that explains the transcriptional regulation of PHLDA2 on in utero growth has yet to be described. In this study, we sequenced the PHLDA2 promoter region in 263 fetal DNA samples to identify polymorphic variants. We used a luciferase reporter assay to identify in the PHLDA2 promoter a 15 bp repeat sequence (RS1) variant that significantly reduces PHLDA2-promoter efficiency. RS1 genotyping was then performed in three independent white European normal birth cohorts. Meta-analysis of all three (total n = 9,433) showed that maternal inheritance of RS1 resulted in a significant 93 g increase in birth weight (p = 0.01; 95% confidence interval [CI] = 22-163). Moreover, when the mother was homozygous for RS1, the influence on birth weight was 155 g (p = 0.04; 95% CI = 9-300), which is a similar magnitude to the reduction in birth weight caused by maternal smoking.

Regional variation in tolvaptan prescribing across England: national data and retrospective evaluation from an expert centre.

Background: Tolvaptan, a vasopressin V2 receptor antagonist, was approved in 2015 by the UK National Institute for Health and Care Excellence for use in patients with autosomal dominant polycystic kidney disease (ADPKD) and rapid disease progression. Simultaneous guidance was issued by the UK Kidney Association (UKKA) to facilitate national implementation. Methods: Data on tolvaptan prescribing in England was obtained through the National Health Service (NHS) Digital, a national survey of all 77 adult kidney units, and the implementation of UKKA guidance was evaluated at an expert PKD centre. Results: A regional variation of up to 4-fold for tolvaptan prescribing in England was found. Despite most kidney units following UKKA guidance, centre-based estimates of eligible or treated patient numbers were highly variable. Retrospective evaluation at an expert PKD centre revealed that in a cohort demonstrating rapid estimated glomerular filtration rate (eGFR) decline, 14% would not be eligible for tolvaptan by Mayo imaging classification and more than half (57%) would not be eligible by Predicting Renal Outcome in Polycystic Kidney Disease score. The 3-year discontinuation rate was higher than expected (56%), the majority (70%) due to aquaretic symptoms. In patients taking tolvaptan for at least 2 years, 81% showed a reduction in the rate of eGFR decline compared with baseline, with earlier disease associated with positive treatment response. Conclusion: Real-world data have revealed a much higher regional variation in tolvaptan prescribing for ADPKD in England than expected. We propose further investigation into the factors responsible for this variation.

Barriers and facilitators to the implementation of guidelines in rare diseases: a systematic review.

BACKGROUND: Rare diseases present a challenge to guideline implementation due to a low prevalence in the general population and the unfamiliarity of healthcare professionals. Existing literature in more common diseases references barriers and facilitators to guideline implementation. This systematic review aims to identify these barriers and facilitators in rare diseases from existing literature. METHODS: A multi-stage strategy included searching MEDLINE PubMed, EMBASE Ovid, Web of Science and Cochrane library from the earliest date available to April 2021, Orphanet journal hand-search, a pearl-growing strategy from a primary source and reference/citation search was performed. The Integrated Checklist of Determinants of Practice which comprises of twelve checklists and taxonomies, informed by 57 potential determinants was selected as a screening tool to identify determinants that warrant further in-depth investigation to inform design of future implementation strategies. RESULTS: Forty-four studies were included, most of which were conducted in the United States (54.5%). There were 168 barriers across 36 determinants (37 studies) and 52 facilitators across 22 determinants (22 studies). Fifteen diseases were included across eight WHO ICD-11 disease categories. Together individual health professional factors and guideline factors formed the majority of the reported determinants (59.5% of barriers and 53.8% of facilitators). Overall, the three most reported individual barriers were the awareness/familiarity with the recommendation, domain knowledge and feasibility. The three most reported individual facilitators were awareness/familiarity with the recommendation, agreement with the recommendation and ability to readily access the guidelines. Resource barriers to implementation included technology costs, ancillary staff costs and more cost-effective alternatives. There was a paucity of studies reporting influential people, patient advocacy groups or opinion leaders, or organisational factors influencing implementation. CONCLUSIONS: Key barriers and facilitators to the implementation of clinical practice guidelines in the setting of rare diseases were at the individual health professional and guideline level. Influential people and organisational factors were relatively under-reported and warrant exploration, as does increasing the ability to access the guidelines as a potential intervention.

Sphingomyelinase Disables Inactivation in Endogenous PIEZO1 Channels.

Endogenous PIEZO1 channels of native endothelium lack the hallmark inactivation often seen when these channels are overexpressed in cell lines. Because prior work showed that the force of shear stress activates sphingomyelinase in endothelium, we considered if sphingomyelinase is relevant to endogenous PIEZO1. Patch clamping was used to quantify PIEZO1-mediated signals in freshly isolated murine endothelium exposed to the mechanical forces caused by shear stress and membrane stretch. Neutral sphingomyelinase inhibitors and genetic disruption of sphingomyelin phosphodiesterase 3 (SMPD3) cause PIEZO1 to switch to profoundly inactivating behavior. Ceramide (a key product of SMPD3) rescues non-inactivating channel behavior. Its co-product, phosphoryl choline, has no effect. In contrast to ceramide, sphingomyelin (the SMPD3 substrate) does not affect inactivation but alters channel force sensitivity. The data suggest that sphingomyelinase activity, ceramide, and sphingomyelin are determinants of native PIEZO gating that enable sustained activity.

Autosomal dominant polycystic kidney disease: recent advances in clinical management.

The first clinical descriptions of autosomal dominant polycystic kidney disease (ADPKD) go back at least 500 years to the late 16 (th) century. Advances in understanding disease presentation and pathophysiology have mirrored the progress of clinical medicine in anatomy, pathology, physiology, cell biology, and genetics. The identification of PKD1 and PKD2, the major genes mutated in ADPKD, has stimulated major advances, which in turn have led to the first approved drug for this disorder and a fresh reassessment of patient management in the 21 (st) century. In this commentary, we consider how clinical management is likely to change in the coming decade.

A deafness-associated mutant human connexin 26 improves the epithelial barrier in vitro.

A large proportion of recessive nonsyndromic hearing loss is due to mutations in the GJB2 gene encoding connexin 26 (Cx26), a component of a gap junction. Within different ethnic groups there are specific common recessive mutations, each with a relatively high carrier frequency, suggesting the possibility of heterozygous advantage. Carriers of the R143W GJB2 allele, the most prevalent in the African population, present with a thicker epidermis than noncarriers. In this study, we show that (R143W)Cx26-expressing keratinocytes form a significantly thicker epidermis in an organotypic coculture skin model. In addition, we show increased migration of cells expressing (R143W)Cx26 compared to (WT)Cx26-overexpressing cells. We also demonstrate that cells expressing (R143W)Cx26 are significantly less susceptible to cellular invasion by the enteric pathogen Shigella flexneri than (WT)Cx26-expressing cells. These in vitro studies suggest an advantageous effect of (R143W)Cx26 in epithelial cells.