Ocular manifestations of congenital anomalies of the kidney and urinary tract (CAKUT).

Congenital anomalies of the kidney and urinary tract (CAKUT) are among the most common birth defects worldwide and a major cause of kidney failure in children. Extra-renal manifestations are also common. This study reviewed diseases associated with the Genomics England CAKUT-associated gene panel for ocular anomalies. In addition, each gene was examined for expression in the human retina and an ocular phenotype in mouse models using the Human Protein Atlas and Mouse Genome Informatics databases, respectively. Thirty-four (54%) of the 63 CAKUT-associated genes (55 'green' and 8 'amber') had a reported ocular phenotype. Five of the 6 most common CAKUT-associated genes (PAX2, EYA1, SALL1, GATA3, PBX1) that represent 30% of all diagnoses had ocular features. The ocular abnormalities found with most CAKUT-associated genes and with five of the six commonest were coloboma, microphthalmia, optic disc anomalies, refraction errors (astigmatism, myopia, and hypermetropia), and cataract. Seven of the CAKUT-associated genes studied (11%) had no reported ocular features but were expressed in the human retina or had an ocular phenotype in a mouse model, which suggested further possibly-unrecognised abnormalities. About one third of CAKUT-associated genes (18, 29%) had no ocular associations and were not expressed in the retina, and the corresponding mouse models had no ocular phenotype. Ocular abnormalities in individuals with CAKUT suggest a genetic basis for the disease and sometimes indicate the affected gene. Individuals with CAKUT often have ocular abnormalities and may require an ophthalmic review, monitoring, and treatment to preserve vision.

Ocular manifestations of renal ciliopathies.

Renal ciliopathies are a common cause of kidney failure in children and adults, and this study reviewed their ocular associations. Genes affected in renal ciliopathies were identified from the Genomics England Panels. Ocular associations were identified from Medline and OMIM, and the genes additionally examined for expression in the human retina ( https://www.proteinatlas.org/humanproteome/tissue ) and for an ocular phenotype in mouse models ( http://www.informatics.jax.org/ ). Eighty-two of the 86 pediatric-onset renal ciliopathies (95%) have an ocular phenotype, including inherited retinal degeneration, oculomotor disorders, and coloboma. Diseases associated with pathogenic variants in ANK6, MAPKBP1, NEK8, and TCTN1 have no reported ocular manifestations, as well as low retinal expression and no ocular features in mouse models. Ocular abnormalities are not associated with the most common adult-onset "cystic" kidney diseases, namely, autosomal dominant (AD) polycystic kidney disease and the AD tubulointerstitial kidney diseases (ADTKD). However, other kidney syndromes with cysts have ocular features including papillorenal syndrome (optic disc dysplasia), Hereditary Angiopathy Nephropathy, Aneurysms and muscle Cramps (HANAC) (tortuous retinal vessels), tuberous sclerosis (retinal hamartomas), von Hippel-Lindau syndrome (retinal hemangiomas), and Alport syndrome (lenticonus, fleck retinopathy). Ocular abnormalities are associated with many pediatric-onset renal ciliopathies but are uncommon in adult-onset cystic kidney disease. However the demonstration of ocular manifestations may be helpful diagnostically and the features may require monitoring or treatment.

Ocular manifestations of the genetic causes of focal and segmental glomerulosclerosis.

Genetic forms of focal and segmental glomerulosclerosis (FSGS) often have extra-renal manifestations. This study examined FSGS-associated genes from the Genomics England Renal proteinuria panel for reported and likely ocular features. Thirty-two of the 55 genes (58%) were associated with ocular abnormalities in human disease, and a further 12 (22%) were expressed in the retina or had an eye phenotype in mouse models. The commonest genes affected in congenital nephrotic syndrome (NPHS1, NPHS2, WT1, LAMB2, PAX2 but not PLCE1) may have ocular manifestations . Many genes affected in childhood-adolescent onset FSGS (NPHS1, NPHS2, WT1, LAMB2, SMARCAL1, NUP107 but not TRPC6 or PLCE1) have ocular features. The commonest genes affected in adult-onset FSGS (COL4A3-COL4A5, GLA ) have ocular abnormalities but not the other frequently affected genes (ACTN4, CD2AP, INF2, TRPC6). Common ocular associations of genetic FSGS include cataract, myopia, strabismus, ptosis and retinal atrophy. Mitochondrial forms of FSGS (MELAS, MIDD, Kearn's Sayre disease) are associated with retinal atrophy and inherited retinal degeneration. Some genetic kidney diseases (CAKUT, ciliopathies, tubulopathies) that result in secondary forms of FSGS also have ocular features. Ocular manifestations suggest a genetic basis for FSGS, often help identify the affected gene, and prompt genetic testing. In general, ocular abnormalities require early evaluation by an ophthalmologist, and sometimes, monitoring or treatment to improve vision or prevent visual loss from complications. In addition, the patient should be examined for other syndromic features and first degree family members assessed.

Drusen and Other Retinal Findings in People With IgA Glomerulonephritis.

PURPOSE: Retinal drusen have been described in people with IgA nephropathy. We examined the frequency of drusen in IgA nephropathy and compared their location and composition with those for drusen in age-related macular degeneration. DESIGN: Immunohistological case series of eyes of patients with IgA nephropathy, and a comparison eye with age-related macular degeneration. METHODS: Donor eyes from 4 individuals (3 male, 1 female, aged 40-80 years) with biopsy-proven IgA nephropathy and kidney failure were examined for the presence of drusen, and location and composition using antibodies for vitronectin, IgA, IgM, IgG, C3, and C1q. Results were compared with those for drusen in macular degeneration without IgA nephropathy. RESULTS: All 4 donors had sparse, subretinal pigment epithelium drusen of 55-65 mm diameter that stained for vitronectin but not for IgA or complement. All donors had retinal capillaries and choriocapillaris staining for IgA. The youngest donor (female, 40) had rare deposits in the outer nuclear layer that stained for IgA, but not for vitronectin. The oldest donor (male, 82) had large cystlike spaces in the inner nuclear and plexiform layers, and smaller cysts in the outer nuclear layer, with no staining for IgA or complement. CONCLUSIONS: Retinal drusen are uncommon in IgA nephropathy, even with kidney failure. Drusen in IgA nephropathy resemble drusen found in age-related macular degeneration. IgA-staining deposits in the outer nuclear layer were likely due to systemic deposition of IgA and complement activation. The nature of cystic spaces is unknown. Further analysis of the retinas of people with glomerulonephritis is recommended.

Tips for Testing Adults With Suspected Genetic Kidney Disease.

Genetic kidney disease is common but often unrecognized. It accounts for most cystic kidney diseases and tubulopathies, many forms of congenital abnormalities of the kidney and urinary tract (CAKUT), and some glomerulopathies. Genetic kidney disease is typically suspected where the disease usually has a genetic basis or there is another affected family member, a young age at onset, or extrarenal involvement, but there are also many exceptions to these "rules". Genetic testing requires the patient's written informed consent. When a patient declines testing, another later conversation may be worthwhile. Genetic testing not only indicates the diagnosis but also the inheritance pattern, likely at-risk family members, disease in other organs, clinical course, and possibly effective treatments. Sometimes genetic testing does not identify a pathogenic variant even where other evidence is strong. A variant of uncertain significance (VUS) may be reported but should not be used for clinical decision making. It may be reclassified after more information becomes available without necessarily retesting the patient. Patients should be provided with a copy of their genetic test report, the results explained, and at-risk family members offered "cascade" testing. A referral to a clinical geneticist or genetic counselor helps identify affected family members and in providing advice to assist with reproductive decisions.

Retinal small vessel narrowing in women with gestational diabetes, pregnancy-associated hypertension, or small-for-gestational age babies.

Background: Gestational diabetes, pregnancy-associated hypertension and small-for-gestational age babies are all associated with impaired placental vascularisation. This study compared the effects of these conditions the systemic small vessel calibre that was examined in the retina. Methods: This was a cross-sectional observational study of consecutive pregnant women recruited from an antenatal clinic. Participants underwent a Glucose Tolerance Test, BP measurements, and were examined for small-for-gestational age babies as per national guidelines. They also underwent retinal photography with a non-mydriatic camera, and vessel calibres were measured with a validated semi-quantitative system at a retinal grading centre. Some participants also underwent testing of retinal vascular responsiveness to a flickering light. Results: Women with gestational diabetes (n = 68) had a higher mean arterial pressure (85 ± 9 mm Hg) than normal pregnant women (n = 27, 80 ± 8 mmHg, p = 0.01). They also had smaller mean retinal arteriole (147.5 ± 13.6 µm and 159.7 ± 6.7 µm respectively, p < 0.01) and venular calibre (221.0 ± 13.4 µm and 232.8 ± 20.1 µm respectively, p < 0.01) than normal. However their babies' mean birth weights were not different from normal (3,311 ± 558 g and 3,401 ± 600 g respectively, p = 0.48). They also demonstrated a trend to reduced retinal arteriolar dilatation (3.5 ± 1.3%, n = 23) in response to vasodilatory stimuli (4.4 ± 1.8%) (n = 11) (p = 0.08) consistent with endothelial dysfunction. Women with pregnancy-associated hypertension (n = 35) had a higher mean arterial pressure (101 ± 12 mm Hg, p < 0.01), a smaller mean retinal arteriolar calibre (139.9 ± 10.6 µm, p < 0.0001), and a lower baby mean birth weight than for normal pregnancies (3,095 ± 443 g, p = 0.02). Likewise, women with small-for-gestational age babies (n = 31) had a higher mean arterial pressure (89 ± 19 mm Hg, p = 0.03), a smaller mean retinal arteriolar calibre (141.6 ± 12.8 µm, p < 0.01) and a lower baby mean birth weight than for normal pregnancies (2,468 ± 324 g, p < 0.0001). Conclusion: Mean retinal arterial calibre was reduced in women with gestational diabetes, pregnancy-associated hypertension or small-for-gestational age babies. The reduction in calibre was greatest in pregnancy-associated hypertension and small-for-gestational age babies. Systemic arteriole narrowing may contribute to the pathogenesis of placental vascular dysfunction in these conditions.

Ocular manifestations of the genetic renal tubulopathies.

BACKGROUND: The genetic tubulopathies are rare and heterogenous disorders that are often difficult to identify. This study examined the tubulopathy-causing genes for ocular associations that suggested their genetic basis and, in some cases, the affected gene. METHODS: Sixty-seven genes from the Genomics England renal tubulopathy panel were reviewed for ocular features, and for retinal expression in the Human Protein Atlas and an ocular phenotype in mouse models in the Mouse Genome Informatics database. The genes resulted in disease affecting the proximal tubules (n = 24); the thick ascending limb of the loop of Henle (n = 10); the distal convoluted tubule (n = 15); or the collecting duct (n = 18). RESULTS: Twenty-five of the tubulopathy-associated genes (37%) had ocular features reported in human disease, 49 (73%) were expressed in the retina, although often at low levels, and 16 (24%) of the corresponding mouse models had an ocular phenotype. Ocular abnormalities were more common in genes affected in the proximal tubulopathies (17/24, 71%) than elsewhere (7/43, 16%). They included structural features (coloboma, microphthalmia); refractive errors (myopia, astigmatism); crystal deposition (in oxalosis, cystinosis) and sclerochoroidal calcification (in Bartter, Gitelman syndromes). Retinal atrophy was common in the mitochondrial-associated tubulopathies. Structural abnormalities and crystal deposition were present from childhood, but sclerochoroidal calcification typically occurred after middle age. CONCLUSIONS: Ocular abnormalities are uncommon in the genetic tubulopathies but may be helpful in recognizing the underlying genetic disease. The retinal expression and mouse phenotype data suggest that further ocular associations may become apparent with additional reports. Early identification may be necessary to monitor and treat visual complications.

Genetic Modifiers of Mendelian Monogenic Collagen IV Nephropathies in Humans and Mice.

Familial hematuria is a clinical sign of a genetically heterogeneous group of conditions, accompanied by broad inter- and intrafamilial variable expressivity. The most frequent condition is caused by pathogenic (or likely pathogenic) variants in the collagen-IV genes, COL4A3/A4/A5. Pathogenic variants in COL4A5 are responsible for the severe X-linked glomerulopathy, Alport syndrome (AS), while homozygous or compound heterozygous variants in the COL4A3 or the COL4A4 gene cause autosomal recessive AS. AS usually leads to progressive kidney failure before the age of 40-years when left untreated. People who inherit heterozygous COL4A3/A4 variants are at-risk of a slowly progressive form of the disease, starting with microscopic hematuria in early childhood, developing Alport spectrum nephropathy. Sometimes, they are diagnosed with benign familial hematuria, and sometimes with autosomal dominant AS. At diagnosis, they often show thin basement membrane nephropathy, reflecting the uniform thin glomerular basement membrane lesion, inherited as an autosomal dominant condition. On a long follow-up, most patients will retain normal or mildly affected kidney function, while a substantial proportion will develop chronic kidney disease (CKD), even kidney failure at an average age of 55-years. A question that remains unanswered is how to distinguish those patients with AS or with heterozygous COL4A3/A4 variants who will manifest a more aggressive kidney function decline, requiring prompt medical intervention. The hypothesis that a subgroup of patients coinherit additional genetic modifiers that exacerbate their clinical course has been investigated by several researchers. Here, we review all publications that describe the potential role of candidate genetic modifiers in patients and include a summary of studies in AS mouse models.

A comparison of the ocular features in Pierson and Alport syndrome: a case report and literature review.

BACKGROUND: Pierson syndrome and X-linked Alport syndrome result from pathogenic variants in LAMB2 and COL4A5, respectively, and both affect basement membranes in the kidney and the eye. This study describes the ocular features in an individual with a homozygous LAMB2 pathogenic variant and compares the reported abnormalities in Pierson syndrome with those in Alport syndrome. METHODS: A 28-year-old man who developed kidney failure 10 years previously and subsequently had an atrial septal defect repair was suspected of having genetic kidney disease on the basis of his likely diagnosis of Focal and Segmental Glomerulosclerosis (FSGS), his young age at presentation, and his cardiac anomaly. He then underwent Whole Exome Sequencing and a formal ophthalmological examination. RESULTS: The patient was found to have a homozygous Likely Pathogenic missense variant (p.(Arg1719Cys)) in LAMB2 consistent with the diagnosis of Pierson syndrome. He had normal visual acuity, normal optic globe and cornea size, and normal lens appearance on direct examination. Upon further testing, his cornea demonstrated central thinning. There was also increased corneal endothelial pleomorphism, a reduced foveal reflex, and a blunted foveal curvature, similar to the features seen in X-linked Alport syndrome. CONCLUSION: Our patient had a later onset form of Pierson syndrome or "FSGS type 5, with or without ocular abnormalities," consistent with his "milder" LAMB2 missense variant. The resemblance of the ocular features in Pierson syndrome and X-linked Alport syndrome suggests that mutations in LAMB2 and COL4A5 have similar effects on basement membranes and the pathogenesis of ocular damage.

Population Frequency of Undiagnosed Fabry Disease in the General Population.

Introduction: Fabry disease is an X-linked disorder that results from pathogenic GLA variants and can now be treated. Most studies of its population frequency have examined only males or attendees at kidney failure or cardiac clinics. This study determined the prevalence of undiagnosed Fabry disease from predicted pathogenic GLA variants in the general population. Methods: The Genome Aggregation Database (gnomAD) was examined for predicted pathogenic GLA variants based on variant rarity (≤5), and transcript effect in 4 computational tools (CADD >20, PP2 >0.95, SIFT <0.05, Mutation Taster - Disease-causing) and amino acid conservation in vertebrates in a Clustal. Results: Predicted pathogenic variants in GLA occurred in 1 in 3225 of the gnomAD population and 1 in 3478 of its control subset. Predicted pathogenic variants were more common in women than expected (3.1:1), which is consistent with men being excluded from gnomAD because of Fabry complications. Predicted pathogenic variants were not found in members of this cohort with South Asian, Ashkenazim, or Finnish ancestries. Variants identified as pathogenic in the Fabry database were found in 1 in 2651 individuals of the gnomAD database and pathogenic variants from ClinVar in 1 in 4420. Discussion: The population frequency of 1 in 3225 for undiagnosed men and women with Fabry disease still represents an underestimate because our pathogenicity criteria were rigorous, the cohort did not include already-diagnosed individuals, and whole exome sequencing does not detect intronic variants and large deletions. This study confirms that Fabry disease is more common than previously recognized and still underdiagnosed especially in women.

What patients want to know about genetic testing for kidney disease.

Previously, genetic kidney disease was often recognised when family members shared clinical features. Now, many genetic kidney diseases are diagnosed when testing demonstrates a pathogenic variant in a gene associated with the disease. Detection of a genetic variant also identifies the mode of inheritance, and suggests family members at risk. The genetic diagnosis has additional advantages for patients and their doctors even when no specific treatment is available since it often indicates likely complications in other organs, the clinical course, and management strategies. Generally, informed consent is required for genetic testing because the result provides "certainty" with implications for the patient, and their family, and possibly for employment, and for life and medical insurance, as well as having social, ethical, and financial consequences. Patients want to be provided with a copy of their genetic test result in a format that is comprehensible and to have the result explained. Their at-risk family members should be sought out and offered genetic testing too. Patients who allow the sharing of their anonymised results in registries help advance everyone's understanding of these diseases and expedite a diagnosis in other families. Patient Support Groups not only help normalise the disease but also educate patients, and update them on recent advances and new treatments. Some registries encourage patients to themselves submit their genetic variants, clinical features and response to treatment. More and more often, patients may volunteer for clinical trials of novel therapies including some that depend on a genetic diagnosis or variant type.

A founder COL4A4 pathogenic variant resulting in autosomal recessive Alport syndrome accounts for most genetic kidney failure in Romani people.

Introduction: Romani people have a high prevalence of kidney failure. This study examined a Romani cohort for pathogenic variants in the COL4A3, COL4A4, and COL4A5 genes that are affected in Alport syndrome (AS), a common cause of genetic kidney disease, characterized by hematuria, proteinuria, end-stage kidney failure, hearing loss, and eye anomalies. Materials and methods: The study included 57 Romani from different families with clinical features that suggested AS who underwent next-generation sequencing (NGS) of the COL4A3, COL4A4, and COL4A5 genes, and 83 family members. Results: In total, 27 Romani (19%) had autosomal recessive AS caused by a homozygous pathogenic c.1598G>A, p.Gly533Asp variant in COL4A4 (n = 20) or a homozygous c.415G>C, p.Gly139Arg variant in COL4A3 (n = 7). For p.Gly533Asp, 12 (80%) had macroscopic hematuria, 12 (63%) developed end-stage kidney failure at a median age of 22 years, and 13 (67%) had hearing loss. For p.Gly139Arg, none had macroscopic hematuria (p = 0.023), three (50%) had end-stage kidney failure by a median age of 42 years (p = 0.653), and five (83%) had hearing loss (p = 0.367). The p.Gly533Asp variant was associated with a more severe phenotype than p.Gly139Arg, with an earlier age at end-stage kidney failure and more macroscopic hematuria. Microscopic hematuria was very common in heterozygotes with both p.Gly533Asp (91%) and p.Gly139Arg (92%). Conclusion: These two founder variants contribute to the high prevalence of kidney failure in Czech Romani. The estimated population frequency of autosomal recessive AS from these variants and consanguinity by descent is at least 1:11,000 in Czech Romani. This corresponds to a population frequency of autosomal dominant AS from these two variants alone of 1%. Romani with persistent hematuria should be offered genetic testing.

KCTD1 and Scalp-Ear-Nipple ('Finlay-Marks') syndrome may be associated with myopia and Thin basement membrane nephropathy through an effect on the collagen IV α3 and α4 chains.

INTRODUCTION: Scalp-Ear-Nipple syndrome is caused by pathogenic KCTD1 variants and characterised by a scalp defect, prominent ears, and rudimentary breasts. We describe here further clinical associations in the eye and kidney. METHODS: Fifteen affected members from two unrelated families with p.(Ala30Glu) or p.(Pro31Leu) in KCTD1 were examined for ocular and renal abnormalities. The relevant proteins were studied in the eye and kidney, and the mutation consequences determined from mouse knockout models. RESULTS: Five males and 10 females with a median age of 40 years (range 1-70) with pathogenic variants p.(Ala30Glu) (n = 12) or p.(Pro31Leu) (n = 3) in KCTD1 were studied. Of the 6 who underwent detailed ophthalmic examination, 5 (83%) had low myopic astigmatism, the mean spherical equivalent of 10 eyes was 2.38D, and one (17%) had hypermetropic astigmatism. One female had a divergent strabismus.Five individuals had renal cysts (5/15, 33%), with renal biopsy in one demonstrating a thinned glomerular basement membrane identical to that seen in Thin basement membrane nephropathy (AD Alport syndrome).In the eye, KCTD1 and its downstream targets, TFAP2, and the collagen IV α3 and α4 chains localised to the cornea and near the retinal amacrine cells. In the kidney, all these proteins except TFAP2 were expressed in the podocytes and distal tubules. TFAP2B and COL4A4 knockout mice also had kidney cysts, and COL4A3 and COL4A4 knockout mice had myopia. CONCLUSION: Individuals with a pathogenic KCTD1 variant may have low myopic astigmatism and represent a further rare genetic cause for a thinned glomerular basement membrane.

A Systematic Review of Pathogenic COL4A5 Variants and Proteinuria in Women and Girls With X-linked Alport Syndrome.

Introduction: Women and girls with X-linked Alport syndrome have a risk of disease progression that is difficult to predict. This systematic review examined whether proteinuria correlated with genotype and disease severity in this population. Methods: PubMed and Scopus were searched for manuscripts from the past 20 years with "COL4A5," "female," "proteinuria" and related terms. Genotypes and clinical data for women and girls with pathogenic heterozygous COL4A5 variants were extracted. Features were then compared between females with proteinuria or without proteinuria; and genotype-phenotype correlations for age at proteinuria and kidney failure determined. Results: Three-hundred sixty-six women and girls with COL4A5 variants and a median age of 29 years (interquartile range 15-46) were identified. Eighty-eight (24%) had large rearrangements or truncating variants, 63 (17%) had splicing variants, and 215 (59%) had missense changes. In all, 236 (64%) had proteinuria, 56 (16%) had kidney failure, 40 (16%) had a hearing loss, and 15 (7%) had ocular abnormalities. Women and girls with proteinuria were more likely to have large rearrangements or truncating variants (P = 0.005), and less likely to have missense changes (P = 0.0002). Those with proteinuria were also more likely to develop kidney failure (P < 0.0001). Women and girls with truncating, large or splicing variants developed proteinuria earlier than those with missense changes (P = 0.001, P < 0.0001 respectively). Those whose proteinuria was detected before the age of 15 progressed to kidney failure sooner (P < 0.0001). Conclusion: Proteinuria correlates with a more severe genotype in women and girls with X-linked Alport syndrome and is an indicator of disease severity and likely progression.

Increased retinal drusen in IgA glomerulonephritis are further evidence for complement activation in disease pathogenesis.

Drusen are retinal deposits comprising cell debris, immune material and complement that are characteristic of macular degeneration but also found in glomerulonephritis. This was a pilot cross-sectional study to determine how often drusen occurred in IgA glomerulonephritis and their clinical significance. Study participants underwent non-mydriatic retinal photography, and their deidentified retinal images were examined for drusen by two trained graders, who compared central drusen counts, counts ≥ 10 and drusen size with those of matched controls. The cohort comprised 122 individuals with IgA glomerulonephritis including 89 males (73%), 49 individuals (40%) of East Asian or Southern European ancestry, with an overall median age of 54 years (34-64), and median disease duration of 9 years (4-17). Thirty-nine (33%) had an eGFR < 60 ml/min/1.73 m2 and 72 had previously reached kidney failure (61%). Overall mean drusen counts were higher in IgA glomerulonephritis (9 ± 27) than controls (2 ± 7, p < 0.001). Central counts ≥ 10 were also more common (OR = 3.31 (1.42-7.73, p = 0.006), and were associated with longer disease duration (p = 0.03) but not kidney failure (p = 0.31). Larger drusen were associated with more mesangial IgA staining (p = 0.004). Increased drusen counts were also present in IgA glomerulonephritis secondary to Crohn's disease but not with Henoch-Schonlein purpura. The finding of retinal drusen in IgA glomerulonephritis is consistent with complement activation and represents a model for better understanding glomerular immune deposition and a supporting argument for treatment with anti-complement therapies.

Heterozygous Pathogenic COL4A3 and COL4A4 Variants (Autosomal Dominant Alport Syndrome) Are Common, and Not Typically Associated With End-Stage Kidney Failure, Hearing Loss, or Ocular Abnormalities.

The term "autosomal dominant (AD) Alport syndrome" is often used to describe the condition associated with heterozygous pathogenic COL4A3 or COL4A4 variants and has largely replaced "thin basement membrane nephropathy (TBMN)." AD Alport syndrome implies that affected individuals develop end-stage kidney failure (ESKF) as well as the typical Alport hearing loss and ocular abnormalities, but these features have been considered rare with TBMN. Recent studies suggest that ESKF occurs in 14% to 30% of those with heterozygous pathogenic COL4A3 or COL4A4 variants but confirm that the hearing loss and ocular defects occur uncommonly if at all. Uncertainty over the risk of ESKF has persisted. However all the cited studies of heterozygous pathogenic COL4A3 or COL4A4 variants and kidney failure are from hospital-based patients and thus biased toward more severe disease. Multiple unselected cohorts with ESKF have found heterozygous pathogenic variants in COL4A3 and COL4A4 occur about as often as COL4A5 variants, which suggests that AD Alport syndrome causes ESKF as often as X-linked (XL) disease. In the normal population, heterozygous pathogenic COL4A3 and COL4A4 variants are present 20 times more often than COL4A5 variants. Therefore, AD Alport syndrome is complicated by ESKF 20 times less often than XL disease and occurs in fewer than 3% of those with pathogenic COL4A3 or COL4A4 variants by the age of 60. Nevertheless, individuals with heterozygous pathogenic COL4A3 or COL4A4 variants referred to a hospital are still more likely to develop impaired kidney function than those who remain at home undiagnosed.