Long-Term Outcomes of Living-Related Kidney Donation for Alport Syndrome Spectrum: A Propensity Score-Matched Analysis.

INTRODUCTION: Data to guide the evaluation of living-related donor candidates for kidney transplant recipients with Alport syndrome (AS) spectrum are limited. We aimed to examine a cohort of living-related donors to recipients with AS and compare their outcomes with a control group to improve understanding of the clinical course and outcomes of living donation in this context. METHODS: Living donors (LDs) of AS recipients and propensity score-matched control LDs without any family history of AS (control group) were followed for major cardiac events, death, post-donation estimated glomerular filtration rate (eGFR), and proteinuria. RESULTS: There were 31 LDs (48.4% male), in whom relationship to AS recipient included mother (45.2%), father (32.3%), sibling (16.1%), grandparent (3.2%), and uncle (3.2%). Long-term outcomes over 10.0 (IQR, 3.0-15.0) years were evaluated in 25 and 25 LDs from study and control groups, respectively. During follow-up, 5 LDs (20.0%) in study group developed major cardiac event (acute coronary ischemia [n = 4] and severe congestive heart failure [n = 1]) after 5.5 (IQR, 4.5-10.3) years, whereas only 2 (8.0%) LDs in control group developed major cardiac events (p = 0.221). New-onset hypertension was higher in study group (56.0%) compared to the control group (16.0%) (p = 0.003). Three donors in study and 2 donors in control group who developed new-onset hypertension died during follow-up (p = 0.297). Major cardiac event rate was significantly higher in donors who developed hypertension after donation (0 vs. 28.0%, p < 0.001). There were no differences between study groups regarding last eGFR and proteinuria levels (p = 0.558 and p = 0.120, respectively). DISCUSSION/CONCLUSION: Although the risk of kidney disease can be minimized by careful donor evaluation, our findings suggest that hypertension risk after the donation is higher than expected in related donors of recipients with AS.

Prevalence Estimates of Predicted Pathogenic COL4A3-COL4A5 Variants in a Population Sequencing Database and Their Implications for Alport Syndrome.

BACKGROUND: The reported prevalence of Alport syndrome varies from one in 5000 to one in 53,000 individuals. This study estimated the frequencies of predicted pathogenic COL4A3-COL4A5 variants in sequencing databases of populations without known kidney disease. METHODS: Predicted pathogenic variants were identified using filtering steps based on the ACMG/AMP criteria, which considered collagen IV α3-α5 position 1 Gly to be critical domains. The population frequencies of predicted pathogenic COL4A3-COL4A5 variants were then determined per mean number of sequenced alleles. Population frequencies for compound heterozygous and digenic combinations were calculated from the results for heterozygous variants. RESULTS: COL4A3-COL4A5 variants resulting in position 1 Gly substitutions were confirmed to be associated with hematuria (for each, P<0.001). Predicted pathogenic COL4A5 variants were found in at least one in 2320 individuals. p.(Gly624Asp) represented nearly half (16 of 33, 48%) of the variants in Europeans. Most COL4A5 variants (54 of 59, 92%) had a biochemical feature that potentially mitigated the clinical effect. The predicted pathogenic heterozygous COL4A3 and COL4A4 variants affected one in 106 of the population, consistent with the finding of thin basement membrane nephropathy in normal donor kidney biopsy specimens. Predicted pathogenic compound heterozygous variants occurred in one in 88,866 individuals, and digenic variants in at least one in 44,793. CONCLUSIONS: The population frequencies for Alport syndrome are suggested by the frequencies of predicted pathogenic COL4A3-COL4A5 variants, but must be adjusted for the disease penetrance of individual variants and for the likelihood of already diagnosed disease and non-Gly substitutions. Disease penetrance may depend on other genetic and environmental factors.

Clinical and Genetic Features of Autosomal Dominant Alport Syndrome: A Cohort Study.

RATIONALE & OBJECTIVE: Alport syndrome is a common genetic kidney disease accounting for approximately 2% of patients receiving kidney replacement therapy (KRT). It is caused by pathogenic variants in the gene COL4A3, COL4A4, or COL4A5. The aim of this study was to evaluate the clinical and genetic spectrum of patients with autosomal dominant Alport syndrome (ADAS). STUDY DESIGN: Retrospective cohort study. SETTING & PARTICIPANTS: 82 families (252 patients) with ADAS were studied. Clinical, genetic, laboratory, and pathology data were collected. OBSERVATIONS: A pathogenic DNA variant in COL4A3 was identified in 107 patients (35 families), whereas 133 harbored a pathogenic variant in COL4A4 (43 families). Digenic/complex inheritance was observed in 12 patients. Overall, the median kidney survival was 67 (95% CI, 58-73) years, without significant differences across sex (P=0.8), causative genes (P=0.6), or type of variant (P=0.9). Microhematuria was the most common kidney manifestation (92.1%), and extrarenal features were rare. Findings on kidney biopsies ranged from normal to focal segmental glomerulosclerosis. The slope of estimated glomerular filtration rate change was-1.46 (-1.66 to-1.26) mL/min/1.73m2 per year for the overall group, with no significant differences between ADAS genes (P=0.2). LIMITATIONS: The relatively small size of this series from a single country, potentially limiting generalizability. CONCLUSIONS: Patients with ADAS have a wide spectrum of clinical presentations, ranging from asymptomatic to kidney failure, a pattern not clearly related to the causative gene or type of variant. The diversity of ADAS phenotypes contributes to its underdiagnosis in clinical practice.

Detection of Splicing Abnormalities and Genotype-Phenotype Correlation in X-linked Alport Syndrome.

BACKGROUND: X-linked Alport syndrome (XLAS) is a progressive hereditary nephropathy caused by mutations in the COL4A5 gene. Genotype-phenotype correlation in male XLAS is relatively well established; relative to truncating mutations, nontruncating mutations exhibit milder phenotypes. However, transcript comparison between XLAS cases with splicing abnormalities that result in a premature stop codon and those with nontruncating splicing abnormalities has not been reported, mainly because transcript analysis is not routinely conducted in patients with XLAS. METHODS: We examined transcript expression for all patients with suspected splicing abnormalities who were treated at one hospital between January of 2006 and July of 2017. Additionally, we recruited 46 males from 29 families with splicing abnormalities to examine genotype-phenotype correlation in patients with truncating (n=21, from 14 families) and nontruncating (n=25, from 15 families) mutations at the transcript level. RESULTS: We detected 41 XLAS families with abnormal splicing patterns and described novel XLAS atypical splicing patterns (n=14) other than exon skipping caused by point mutations in the splice consensus sequence. The median age for developing ESRD was 20 years (95% confidence interval, 14 to 23 years) among patients with truncating mutations and 29 years (95% confidence interval, 25 to 40 years) among patients with nontruncating mutations (P=0.001). CONCLUSIONS: We report unpredictable atypical splicing in the COL4A5 gene in male patients with XLAS and reveal that renal prognosis differs significantly for patients with truncating versus nontruncating splicing abnormalities. Our results suggest that splicing modulation should be explored as a therapy for XLAS with truncating mutations.

A kidney-disease gene panel allows a comprehensive genetic diagnosis of cystic and glomerular inherited kidney diseases.

Molecular diagnosis of inherited kidney diseases remains a challenge due to their expanding phenotypic spectra as well as the constantly growing list of disease-causing genes. Here we develop a comprehensive approach for genetic diagnosis of inherited cystic and glomerular nephropathies. Targeted next generation sequencing of 140 genes causative of or associated with cystic or glomerular nephropathies was performed in 421 patients, a validation cohort of 116 patients with previously known mutations, and a diagnostic cohort of 207 patients with suspected inherited cystic disease and 98 patients with glomerular disease. In the validation cohort, a sensitivity of 99% was achieved. In the diagnostic cohort, causative mutations were found in 78% of patients with cystic disease and 62% of patients with glomerular disease, mostly familial cases, including copy number variants. Results depict the distribution of different cystic and glomerular inherited diseases showing the most likely diagnosis according to perinatal, pediatric and adult disease onset. Of all the genetically diagnosed patients, 15% were referred with an unspecified clinical diagnosis and in 2% genetic testing changed the clinical diagnosis. Therefore, in 17% of cases our genetic analysis was crucial to establish the correct diagnosis. Complex inheritance patterns in autosomal dominant polycystic kidney disease and Alport syndrome were suspected in seven and six patients, respectively. Thus, our kidney-disease gene panel is a comprehensive, noninvasive, and cost-effective tool for genetic diagnosis of cystic and glomerular inherited kidney diseases. This allows etiologic diagnosis in three-quarters of patients and is especially valuable in patients with unspecific or atypical phenotypes.

Novel evidence on hepatitis C virus-associated glomerular disease.

A large spectrum of renal pathology is associated with hepatitis C virus (HCV). According to novel evidence, occult HCV infection (HCV-RNA in peripheral blood mononuclear cells or in serum after ultracentrifugation) could be involved in the pathogenesis of glomerular nephropathy among patients negative for conventional markers of HCV. Additional studies with appropriate size and technology are in progress to confirm the relationship between occult HCV and glomerular disease, which has multiple implications from the clinical standpoint.

High prevalence of occult hepatitis C virus infection in patients with primary and secondary glomerular nephropathies.

The association of hepatitis C virus (HCV) infection and glomerulonephritis is well known. However, the relationship between immune-mediated glomerulonephritis and occult HCV, characterized by the presence of HCV-RNA in liver or in peripheral blood mononuclear cells in the absence of serological markers, is unknown. We tested this in 113 anti-HCV-negative patients; 87 with immune-mediated glomerulonephritis and 26 controls with hereditary glomerular nephropathies. All patients were serum HCV-RNA negative by conventional real-time PCR. Significantly, occult HCV-RNA (detectable viral RNA in peripheral blood mononuclear cells or in serum after ultracentrifugation) was found in 34 of 87 patients with immune-mediated glomerulonephritis versus 1 of 26 control patients. The serum creatinine levels were significantly higher in patients with immune-mediated glomerulonephritis with than in those without occult HCV (1.5 versus 1.1 mg/dl, respectively). A multivariate analysis adjusted for gender showed a significantly increased risk of occult HCV in patients with immune-mediated glomerulonephritis versus the controls (odds ratio of 13.29). Progression to end-stage renal disease tended to be faster in patients with immune-mediated glomerulonephritis and occult HCV than in the negative cases. Thus, occult HCV is strongly associated with immune-mediated glomerulonephritis and may have a role in the progression of the disease.

End-stage kidney disease due to Alport syndrome: outcomes in 296 consecutive Australia and New Zealand Dialysis and Transplant Registry cases.

BACKGROUND: Alport syndrome is a rare inheritable renal disease. Clinical outcomes for patients progressing to end-stage kidney disease (ESKD) are not well described. METHODS: This study aimed to investigate the characteristics and clinical outcomes of patients from Australia and New Zealand commencing renal replacement therapy (RRT) for ESKD due to Alport syndrome between 1965 and 1995 (early cohort) and between 1996 and 2010 (contemporary cohort) compared with propensity score-matched, RRT-treated, non-Alport ESKD controls. RESULTS: A total of 58 422 patients started RRT during this period of which 296 (0.5%) patients had Alport ESKD. In the early cohort, Alport ESKD was associated with superior dialysis patient survival [adjusted hazard ratio (HR): 0.41, 95% confidence interval (CI): 0.20-0.83, P = 0.01], renal allograft survival (HR: 0.74, 95% CI: 0.54-1.01, P = 0.05) and renal transplant patient survival (HR: 0.43, 95% CI: 0.28-0.66, P < 0.001) compared with controls. In the contemporary cohort, no differences were observed between the two groups for dialysis patient survival (HR: 1.42, 95% CI: 0.65-3.11, P = 0.38), renal allograft survival (HR: 1.01, 95% CI: 0.57-1.79, P = 0.98) or renal transplant patient survival (HR: 0.67, 95% CI: 0.26-1.73, P = 0.41). One Alport patient (0.4%) had post-transplant anti-glomerular basement membrane (anti-GBM) disease. Four female and 41 male Alport patients became parents on RRT with generally good neonatal outcomes. CONCLUSION: Alport syndrome patients experienced comparable dialysis and renal transplant outcomes to matched non-Alport ESKD controls in the contemporary cohort due to relatively greater improvements in outcomes for non-Alport ESKD patients over time. Post-transplant anti-GBM disease was rare.

Genotype-phenotype correlations for COL4A3-COL4A5 variants resulting in Gly substitutions in Alport syndrome.

Alport syndrome is the commonest inherited kidney disease and nearly half the pathogenic variants in the COL4A3-COL4A5 genes that cause Alport syndrome result in Gly substitutions. This study examined the molecular characteristics of Gly substitutions that determine the severity of clinical features. Pathogenic COL4A5 variants affecting Gly in the Leiden Open Variation Database in males with X-linked Alport syndrome were correlated with age at kidney failure (n = 157) and hearing loss diagnosis (n = 80). Heterozygous pathogenic COL4A3 and COL4A4 variants affecting Gly (n = 304) in autosomal dominant Alport syndrome were correlated with the risk of haematuria in the UK 100,000 Genomes Project. Gly substitutions were stratified by exon location (1 to 20 or 21 to carboxyl terminus), being adjacent to a non-collagenous region (interruption or terminus), and the degree of instability caused by the replacement residue. Pathogenic COL4A5 variants that resulted in a Gly substitution with a highly destabilising residue reduced the median age at kidney failure by 7 years (p = 0.002), and age at hearing loss diagnosis by 21 years (p = 0.004). Substitutions adjacent to a non-collagenous region delayed kidney failure by 19 years (p = 0.014). Heterozygous pathogenic COL4A3 and COL4A4 variants that resulted in a Gly substitution with a highly destabilising residue (Arg, Val, Glu, Asp, Trp) were associated with an increased risk of haematuria (p = 0.018), and those adjacent to a non-collagenous region were associated with a reduced risk (p = 0.046). Exon location had no effect. In addition, COL4A5 variants adjacent to non-collagenous regions were over-represented in the normal population in gnomAD (p < 0.001). The nature of the substitution and of nearby residues determine the risk of haematuria, early onset kidney failure and hearing loss for Gly substitutions in X-linked and autosomal dominant Alport syndrome.

Genotype-phenotype correlation in X-linked Alport syndrome.

Mutations in the COL4A5 gene cause X-linked Alport syndrome (XLAS). Understanding the correlation between clinical manifestations and the underlying mutations adds prognostic value to genetic testing, which is increasingly available. Our aim was to determine the association between genotype and phenotype in 681 affected male participants with XLAS from 175 US families. Hearing loss and ocular changes were present in 67 and 30% of participants, respectively. Average age of participants at onset of ESRD was 37 years for those with missense mutations, 28 years for those with splice-site mutations, and 25 years for those with truncating mutations (P < 0.0001). We demonstrated a strong relationship between mutation position and age at onset of ESRD, with younger age at onset of ESRD associated with mutations at the 5' end of the gene (hazard ratio 0.766 [95% confidence interval 0.694 to 0.846] per 1000 bp toward the 3' end; P < 0.0001). Affected participants with splice mutations or truncating mutations each had two-fold greater odds of developing eye problems than those with missense mutations; development of hearing impairment showed a similar trend. Hearing loss and ocular changes associated with mutations located closer to the 5; end of the gene. These strong genotype-phenotype correlations could potentially help in the evaluation and counseling of US families with XLAS.

Molecular testing for adult type Alport syndrome.

BACKGROUND: Alport syndrome (AS) is a progressive renal disease with cochlear and ocular involvement. The majority of AS cases are X-linked (XLAS) and due to mutations in the COL4A5 gene. Although the disease may appear early in life and progress to end stage renal disease (ESRD) in young adults, in other families ESRD occurs in middle age. Few of the more than four hundred mutations described in COL4A5 are associated with adult type XLAS, but the families may be very large. METHODS: We classified adult type AS mutation by prevalence in the US and we developed a molecular assay using a set of hybridization probes that identify the three most common adult type XLAS mutations; C1564S, L1649R, and R1677Q. RESULTS: The test was validated on samples previously determined to contain one or none of these mutations. In the US, the test's clinical specificity and sensitivity are estimated to be higher than 99% and 75% respectively. Analytical specificity and sensitivity are above 99%. CONCLUSION: This test may be useful for presymptomatic and carrier testing in families with one of the mutations and in the diagnosis of unexplained hematuria or chronic kidney disease.

Clinical and Pathological Analysis of 4910 Patients Who Received Renal Biopsies at a Single Center in Northeast China.

PURPOSE: To identify the epidemiology and pathological types of kidney diseases and their changes during the past decade, in a population from Northeast China. METHODS: We retrospectively analysed clinical and renal pathological data from 4910 patients who received renal biopsies in the Second Hospital of Jilin University from 2008 to 2017. RESULTS: Males received more renal biopsies than females (p < 0.001). The average age (p < 0.001) and percentage of elderly patients (p < 0.001) increased over time. The pathological types were primary glomerulonephritis (PGN, 73.2%), secondary glomerulonephritis (SGN, 23.7%), tubular-interstitial nephropathy (TIN, 2.8%), and hereditary nephropathy (HN, 0.3%). The most common forms of PGN were membranous nephropathy (MN, 37.2%) and IgA nephropathy (IgAN, 29.9%). Over time, the prevalence of IgAN decreased, but the prevalence of MN increased. MN was more common in middle-aged and elderly patients, but IgAN was most common in young adults. Analysis of SGN data indicated that lupus nephritis (LN, 34.0%), Henoch-Schönlein purpura glomerulonephritis (HSPN, 17.9%), and diabetic nephropathy (DN, 11.7%) were the most common forms. Over time, the prevalence of DN (p = 0.003), hypertension-associated renal damage (p = 0.005), and systemic vasculitis-associated nephritis (SVARD, p < 0.001) increased, but the prevalence of HSPN (p < 0.001) and hepatitis B virus-associated glomerulonephritis (HBV-GN, p = 0.001) decreased. Nephrotic syndrome was the main clinical manifestation of PGN. CONCLUSION: From 2008 to 2017, renal biopsies were increasingly performed in the elderly. There were notable changes in the epidemiology and pathological types of kidney disease among renal biopsy patients at our centre.

Benign familial hematuria due to mutation of the type IV collagen alpha4 gene.

Benign familial hematuria (BFH) is characterized by autosomal dominant inheritance, thinning of the glomerular basement membrane (GBM) and normal renal function. It is frequent in patients with persistent microscopic hematuria, but cannot be clinically differentiated from the initial stages of Alport syndrome, a severe GBM disorder which progresses to renal failure. We present here linkage of benign familial hematuria with the COL4A3 and COL4A4 genes at 2q35-37 (Zmax = 3.58 at theta = 0.0). Subsequently, a glycine to glutamic acid substitution was identified in the collagenous region of the COL4A4 gene. We conclude that type IV collagen defects cause both benign hematuria and Alport syndrome. Furthermore, our data suggest that BFH patients can be carriers of autosomal recessive Alport syndrome.

Mutation analysis of COL4A3 and COL4A4 genes in a Chinese autosomal-dominant Alport syndrome family.

Autosomal dominant Alport syndrome (ADAS) accounts for 5% of all cases of Alport syndrome (AS), a primary basement membrane disorder arising from mutations in genes encoding the type IV collagen protein family.Mutations in COL4A3 and COL4A4 genes were reported to be associated with ADAS. In this study, clinical data in a large consanguineous family with seven affected members were reviewed, and genomic DNA was extracted. For mutation screening, all exons of COL4A3 and COL4A4 genes were polymerase chain reaction-amplified and direct sequenced from genomic DNA, and the mutations were analyzed by comparing with members in this family, 100 ethnicitymatched controls and the sequence of COL4A3 and COL4A4 genes from GenBank. A novel mutation determining a nucleotide change was found, i.e. c.4195 A>T (p.Met1399Leu) at 44th exon of COL4A4 gene, and this mutation showed heterozygous in all patients of this family. Also a novel intron mutation (c.4127+11 C>T) was observed at COL4A4 gene. Thus the novel missense mutation c.4195 A>T (p.Met1399Leu) and the intron mutation (c.4127+11 C>T) at COL4A4 gene might be responsible for ADAS of this family. Our results broadened the spectrum of mutations in COL4A4 and had important implications in the diagnosis, prognosis, and genetic counselling of ADAS.

Familial juvenile hyperuricaemic nephropathy is not such a rare genetic metabolic purine disease in Britain.

Renal disease is rare today in classic adult gout, and gout is rare in renal disease--especially in the young. Here we summarise studies in 158 patients from 31 kindreds diagnosed with familial juvenile hyperuricaemic nephropathy FJHN from a total of 230 kindred members studied in Great Britain. Some patients have been followed for up to 30 years, and allopurinol has ameliorated the progression of the renal disease in all 113 surviving members provided: They have been diagnosed and treated sufficiently early. Compliance with allopurinol treatment and diet has been as important as early recognition. Hypertension has been rigorously controlled. The use of oral contraceptives has been avoided, as has pregnancy in any female with a Glomelar Filtration Rate GFR <70 ml/min. The question arising is: Why is FJHN the most prevalent genetic purine disorder diagnosed in Britain? Is it a lack of awareness which needs to be improved Europe-wide?

Alport syndrome in southern Sweden.

AIM: The aim of the present investigation is to study the epidemiology of Alport syndrome in southern Sweden, to search for mutations in the COL4A5 gene and to estimate the mutation frequency. PATIENTS AND METHODS: Patients with suspected Alport syndrome were identified in an area with a population of 1.45 million. Clinical criteria were used to establish the diagnosis and samples for mutation analysis were collected. Mutation analyses were performed with Single-Stranded Conformation Polymorphism analysis (SSCP) of PCR-amplified genomic DNA. RESULTS: Altogether 25 families with hereditary nephritis were identified. Alport syndrome with X-linked transmission was evident in 14 families, with juvenile (< 31 years) progression to end-stage renal failure (ESRF) in ten, and adult (> or = 31 years) in four families. CONCLUSION: The frequency of males with X-linked disease was calculated to one in 17,000 male births (95% confidence interval (CI) 1/10,500-1/28,600), and the prevalence to one in 40,000. A total of seven females with ESRF were identified, with a median age at ESRF of 45 years. The male to female ratio of cases with ESRF was 4.9 to 1. The risk of developing ESRF among females was from the expected incidence roughly estimated to 12%. Patients with X-linked disease constituted 1.8% of patients with ESRF in the examined area. A mutation was identified positive in 10 of 14 families with X-linked disease, but never in families not fulfilling the clinical criteria for Alport syndrome. In families with juvenile phenotype and positive mutation analysis, the mutation frequency was calculated to between 1/78,000 and 1/198,000 (95% CI 1/42,000-1/177,000) if the effective fertility was estimated to be between 0 and 0.2.

[From Alport syndrome to benign familial hematuria: clinical and genetic aspect]. / Du syndrome d'Alport à l'hématurie familiale bénigne: aspects cliniques et génétiques.

Alport syndrome (AS) is a hereditary glomerulonephritis variably associated with neural hearing loss and ocular abnormalities. The prevalence of the disease is estimated at approximately 1 in 50,000 live births. AS arises from mutations in genes encoding alpha chains constituting type IV collagen. In 85% of patients, the disease results from mutations in the COL4A5 gene located on X chromosome. In the hemizygous male, persistent microhematuria is present from early life, then proteinuria and renal insufficiency occur with time, leading to end-stage renal failure before age 40. In the heterozygous female, clinical manifestations vary from completely healthy state to end-stage renal failure, most often reached after the age of 40. In 15% of patients, the disease results from mutations in either the COL4A3 or the COL4A4 gene, both located on chromosome 2. When both alleles are mutated (autosomal recessive form), the phenotype is constantly severe, resembling that of the hemizygous male in the X-linked form. In the heterozygous individual, the clinical spectrum vary from the absence of any manifestation to the development of proteinuria - the so-called autosomal-dominant AS -, and even renal insufficiency, sometimes reaching end-stage (after the age of 40) through the most frequently encountered phenotype, i.e. a persistently isolated microhematuria, accounting for the so-called benign familial hematuria (or healthy carrier state). The determinants of the phenotype remain largely unknown, so that it may be risky to predict renal prognosis in the individual with a single COL4A3/A4 mutation and an isolated microhematuria at the time of examination.

A comparison of the clinical, histopathologic, and ultrastructural phenotypes in carriers of X-linked and autosomal recessive Alport's syndrome.

Previous series that described phenotypes in carriers of Alport's syndrome did not distinguish genetically between carriers of X-linked and autosomal recessive disease. In this study, modes of inheritance in unselected families with Alport's syndrome associated with two city and two provincial hospitals were determined using microsatellite markers, and carriers of disease haplotypes were identified within these families. All 47 carriers (100%) from 18 families with X-linked Alport's syndrome had dysmorphic hematuria on phase-contrast microscopy, but few developed renal failure (3 of 40 carriers; 8%), clinical hearing loss (2 of 45 carriers; 4%), retinopathy (1 of 30 carriers; 3%), or lenticonus (0 of 30 carriers; 0%). Eleven of the 14 carriers (79%) from 2 families with autosomal recessive disease had dysmorphic hematuria, but none had renal failure, clinical hearing loss, retinopathy, or lenticonus. Urinary red blood cell counts in carriers of X-linked Alport's syndrome were greater than those in carriers of autosomal recessive disease (P < 0.0001), but the frequency of proteinuria and hypertension and levels of proteinuria were not different. There was more tubulointerstitial damage in carriers of X-linked disease (P = 0.012); however, carriers of autosomal recessive disease had more widespread and more uniform thinning of the glomerular basement membrane (P < 0.0001) and less lamellation (P < 0.04).

Major COL4A5 gene rearrangements in patients with juvenile type Alport syndrome.

Mutations in the COL4A5 gene, which encodes the a5 chain of type IV collagen, are found in a large fraction of patients with X-linked Alport syndrome. The recently discovered COL4A6, tightly linked and highly homologous to COL4A5, represents a second candidate gene for Alport syndrome. We analyzed 177 Italian Alport syndrome families by Southern blotting using cDNA probes from both COL4A5 and COL4A6. Nine unrelated families, accounting for 5% of the cases, were found to have a rearrangement in COL4A5. No rearrangements were found in COL4A6, with the exception of a deletion encompassing the 5' ends of both COL4A5 and COL4A6 genes in a patient with Alport syndrome and leiomyomatosis. COL4A5 rearrangements were all intragenic and included 1 duplication and 7 deletions. Polymerase chain reaction (PCR) analysis was carried out to characterize deletion and duplication boundaries and to predict the resulting protein abnormality. The two smallest deletions involved a single exon (exons 17 and 40, respectively), while the largest ones spanned exons 1 to 36. The clinical phenotype of patients in whom a rearrangement in COL4A5 was detected was severe, with progression to end-stage renal failure in juvenile age and hypoacusis occurring in most cases. These data have some important implications in the diagnosis of patients with Alport syndrome.

Type-IV collagen related diseases.

Alport syndrome (ATS) is a progressive inherited glomerulonephritis accounting for 1-2% of all patients who start renal replacement therapy, with an estimated gene frequency of approximately 1 in 5000. ATS is a genetically heterogeneous disease, commonly inherited as an X-linked semi-dominant trait, caused by mutations in COL4A5, on the X-chromosome, and only rarely (less than 10% of cases) caused by the COL4A3 or the COL4A4 gene on chromosome 2q. In the X-linked form females are generally less affected than males, microhematuria being the only sign present throughout life, although approximately 30% can progress to end-stage renal disease. It became evident in recent years that mutations in the COL4A3 or the COL4A4 gene can give rise not only to autosomal recessive ATS syndrome, in which males and females are severely affected, but also to an autosomal dominant form, where the clinical progression towards impaired renal function can be very slow and also to benign familial hematuria (BFH) in which renal function is preserved.