Genotype-phenotype correlation of X-linked Alport syndrome observed in both genders: a multicenter study in South Korea

Genotype-first analysis in an unselected health system-based population reveals variable phenotypic severity of COL4A5 variants

Introduction

Our knowledge of X-linked Alport Syndrome [AS] comes mostly from selected cohorts with more severe disease.

Methods

We examined the phenotypic spectrum of X-linked AS in males and females with a genotype-based approach using data from the Geisinger MyCode DiscovEHR study, an unselected health system-based cohort with exome sequencing and electronic health record data. Patients with COL4A5 variants reported as pathogenic (P) or likely pathogenic (LP) in ClinVar, or protein-truncating variants (PTVs), were each matched with up to 5 controls without COL4A3/4/5 variants by sociodemographics, diabetes diagnosis, and year of first outpatient encounter. AS-related phenotypes included dipstick hematuria, bilateral sensorineural hearing loss (BSHL), proteinuria, decreased eGFR, and ESKD.

Results

Out of 170,856 patients, there were 30 hemizygous males (mean age 52.4 [SD 19.8] years) and 56 heterozygous females (mean age 58.5 [SD 19.4]) with a COL4A5 P/LP variant, including 48 with the hypomorphic variant p.Gly624Asp. Overall, penetrance (having any AS phenotypic feature) was highest for non-p.Gly624Asp P/LP variants (males: 89%, females: 86%), intermediate for p.Gly624Asp (males: 77%, females: 69%), compared to controls (males: 32%; females: 50%). The proportion with ESKD was highest for males with P/LP variants (41%), intermediate for males with p.Gly624Asp (15%) and females with P/LP variants (10%), compared to controls (males: 3%, females 2%). Only 33% of males and 11% of females had a known diagnosis of Alport syndrome or thin basement membrane disease. Only 47% of individuals with COL4A5 had completed albuminuria screening, and a minority were taking renin-angiotensin aldosterone system (RAAS) inhibitors.

Conclusion

In an unselected cohort, we show increased risks of AS-related phenotypes in men and women compared to matched controls, while showing a wider spectrum of severity than has been described previously and variability by genotype. Future studies are needed to determine whether early genetic diagnosis can improve outcomes in Alport Syndrome.

Alport syndrome and Alport kidney diseases - elucidating the disease spectrum

PURPOSE OF REVIEW

With the latest classification, variants in three collagen IV genes, COL4A3 , COL4A4 , and COL4A5 , represent the most prevalent genetic kidney disease in humans, exhibiting diverse, complex, and inconsistent clinical manifestations. This review breaks down the disease spectrum and genotype-phenotype correlations of kidney diseases linked to genetic variants in these genes and distinguishes "classic" Alport syndrome (AS) from the less severe nonsyndromic genetically related nephropathies that we suggest be called "Alport kidney diseases".

RECENT FINDINGS

Several research studies have focused on the genotype-phenotype correlation under the latest classification scheme of AS. The historic diagnoses of "benign familial hematuria" and "thin basement membrane nephropathy" linked to heterozygous variants in COL4A3 or COL4A4 are suggested to be obsolete, but instead classified as autosomal AS by recent expert consensus due to a significant risk of disease progression.

SUMMARY

The concept of Alport kidney disease extends beyond classic AS. Patients carrying pathogenic variants in any one of the COL4A3/A4/A5 genes can have variable phenotypes ranging from completely normal/clinically unrecognizable, hematuria without or with proteinuria, or progression to chronic kidney disease and kidney failure, depending on sex, genotype, and interplays of other genetic as well as environmental factors.

Whole exome sequencing approach for identification of the molecular etiology in pediatric patients with hematuria

BACKGROUND

Hematuria is a common condition in clinical practice of pediatric patients. It is related to a wide spectrum of disorders and has high heterogeneity both clinically and genetically, which contributes to challenges of diagnosis and lead many pediatric patients with hematuria not to receive accurate diagnosis and early management.

METHODS

In this single center study, 42 children with hematuria were included in Tianjin Children's Hospital between 2019 and 2020. We analyzed the clinical information and performed WES (Whole exome sequencing) for all cases. Then the classification of identified variants was performed according to the American College of Medical Genetics and Genomics (ACMG) guidelines for interpreting sequence variants. For the fragment deletion, qPCR was performed to validate and confirm the inherited pattern.

RESULTS

For the 42 patients, 16 cases had gross hematuria and 26 had microscopic hematuria. Molecular genetic causes were uncovered in 9 (21.4%) children, including 7 with Alport syndrome (AS), one with polycystic nephropathy and one with lipoprotein glomerulopathy. The genetic causes for other patients were not related with hematuria.

CONCLUSIONS

WES is a rapid and effective way to evaluate patients with hematuria. The analysis of genotype-phenotype correlations of patients with AS indicated that severe variants were associated with early kidney failure. Secondary findings were not rare in Chinese children, thus the clinician should pay more attention to the clinical interpretation of sequencing results and properly interaction with patients and their family.