Deciphering the pathogenicity of COL4A4 heterozygous splicing mutations and the genotype-phenotype correlation in autosomal dominant Alport syndrome / 中华肾脏病杂志

Objective:Through the investigation of the pathogenicity of COL4A4 heterozygous splicing mutations and the genotype-phenotype correlation in autosomal dominant Alport syndrome (ADAS), to better understand the impact of COL4A4 heterozygous splicing mutations on ADAS. Methods:The study was a case series analysis. Patients from 5 ADAS families with COL4A4 heterozygous splicing mutations detected by whole exome sequencing were recruited by three hospitals. In vivo transcriptional analysis and/or in vitro minigene splicing assay were conducted to determine the splicing patterns and assess the pathogenicity of COL4A4 heterozygous splicing mutations. Results:In the five ADAS pedigrees carrying COL4A4 heterozygous splicing mutations, four novel ADAS splicing patterns were described. In pedigree 1-4, most patients presented with continuous hematuria or/and microalbuminuria. Otherwise,the proband in pedigree 4 presented with macroalbuminuria and the proband in pedigree 1 had progressed to chronic kidney disease stage 2 at the age of 70 years old. In pedigree 5, all patients developed end-stage renal disease between 28 and 41 years old. c.735+3A>G detected in pedigree 1 and pedigree 2 and c.694-1G>C detected in pedigree 3 both led to exon 12 skipping in COL4A4, resulting in 42 nucleotides in-frame deletion (c.694_735del). c.2056+3A>G detected in pedigree 4 led to COL4A4 exon 26 skipping, which caused in-frame deletion of 69 nucleotides (c.1988_2056del). c.2716+5G>T detected in pedigree 5 led to a 360 nucleotides large in-frame deletion, including 100 bp sequence at the 3'end of exon 29,the whole sequence of exon 30 and 89 bp sequence at the 5'end of exon 31 (c.2446_2805del). Conclusions:Renal prognosis differs significantly for patients with small in-frame deletions versus large in-frame deletion splicing abnormalities. Determination of the pathogenicity and the splicing patterns of COL4A4 heterozygous splicing mutations using in vivo and in vitro transcriptional analysis may provide renal prognostic information.

Clinical characteristics and gene analysis of a family with autosomal dominant Alport syndrome with the onset of nephrotic syndrome / 中华实用儿科临床杂志

The clinical characteristics, mutation analysis results, and family tree of a patient with autosomal dominant Alport syndrome (ADAS), who had nephrotic syndrome as the first manifestation were examined.The proband was a 11-month-old girl who presented with nephrotic syndromes and gross hematuria.During the treatment course, the patient had steroid resistance and a poor response to Cyclosporine and Cyclophosphamide pulse therapy.Renal biopsy was performed 2 years after disease onset.Under the light microscopy, glomerular segmental mesangio-proliferative lesions were observed.The staining of type Ⅳ collagen showed the loss of the α3 chain in the glomerular basement membrane (GBM) and tubular basement membrane, and α5 chain loss in GBM.Electron microscopy showed uneven thickness of GBM, with obviously delaminated and tearing dense basement membrane (BM) layer, showing a typical lace-like change.The segmental BM was loosened and widened.Her father did not develop microscopic hematuria until 10 years later, while her grandmother had asymptomatic hematuria and proteinuria when the proband was diagnosed.A new mutation in the COL4A4 gene was found in the proband, namely c. 1715delG (p.G572Vfs * 81). Her father and grandmother carried the same mutation, but her mother and sister did not have.The clinical manifestation of ADAS is clinically heterogeneous and its incidence may be higher than what we have expected.

Una nueva variante del gen COL4A4 (c.1856G> A). De un caso de glomeruloesclerosis focal y segmentaria a una familia con síndrome de Alport / A novel COL4A4 gene variant (c.1856G>A): from a focal segmental glomerulosclerosis case to a family with Alport syndrome

El síndrome de Alport (SA), también conocido como nefritis hereditaria, es una forma progresiva hereditaria de enfermedad glomerular que a menudo se asocia con pérdida auditiva neurosensorial y anomalías oculares. Es causada por mutaciones en los genes que codifican varios miembros de las proteínas de colágeno del tipo IV, que se hallan en las membranas basales principalmente. Los análisis genéticos de las familias afectadas han identificado cuatro modos diferentes de transmisión en pacientes con síndrome de Alport. La forma del síndrome ligada al X surge a partir de mutaciones de COL4A5 y COL4A6 en el cromosoma X, mientras que las formas autosómicas resutan de defectos genéticos tanto en el gen COL4A3 como en el COL4A4, en el cromosoma 2q35-37. Las formas digénicas incluyen pacientes con mutaciones coexistentes en COL4A3, COL4A4 y COL4A5. El resultado clínico a largo plazo en pacientes con SA con mutaciones heterocigotas de COL4A3/A4es generalmente impredecible. La glomeruloesclerosis focal y segmentaria suele desarrollarse en el SA clásico en etapas posteriores y se presenta predominantemente con proteinuria asociada con hematuria. En el caso índice presentado en este informe, a un hombre de 26 años se le realizó una biopsia de riñón debido a una proteinuria nefrótica y una hematuria microscópica acompañada de una función renal alterada. Se le diagnosticó glomeruloesclerosis focal y segmentaria. Debido a que tenía una pérdida auditiva progresiva desde el inicio del estudio, se le realizó un estudio genético de mutaciones en los genes COL4A3 y COL4A4. Se detectó una nueva mutación en el gen COL4A4 (c.1804-7T> C).Debido a que sus padres tenían un matrimonio consanguíneo, el resto de la familia fue sometida a estudio para la misma variante. Sus padres y su hermana fueron heterocigotos y homocigota para la misma variante, respectivamente. En este estudio, se demostró la existencia de una familia con síndrome de Alport con una nueva mutación en el gen COL4A4 (c.1856G> A) que, según sabemos, es el primer caso reportado.

Alport syndrome, also known as hereditary nephritis, is an inherited progressive form of glomerular disease that is often associated with sensorineural hearing loss and ocular abnormalities. It is caused by mutations in genes encoding several members of type IV colagen proteins primarily found in basement membranes. Genetic analyses of affected families have identified four different modes of transmission in patients with Alport syndrome. X-linked form of the syndrome arises from mutations of COL4A5 and COL4A6 on chromosome X, whereas autosomal forms result from genetic defects in either the COL4A3 or COL4A4 genes at chromosome 2q35-37. Digenic forms include patients with coexisting mutations in COL4A3, COL4A4, and COL4A5. The long-term clinical outcome in AS patients with heterozygous COL4A3/A4 mutations is generally unpredictable. Focal segmental glomerulosclerosis usually develops in classical AS at later stages and presents predominantly with proteinuria associated with hematuria. The index case presented in this report, a 26-year-old man, had kidney biopsy because of nephrotic proteinuria and microscopic hematuria accompanied by impaired renal function. He diagnosed focal segmental glomerulosclerosis. As he had progressive hearing loss since chidhood we conducted a genetic study for mutations in COL4A3 and COL4A4 genes. A novel mutation in COL4A4 gene (c.1804-7T>C) was detected. As his parents had consanguineous marriage we investigated the rest of the family for the same variant. His parents, and his sister were found to be heterozygote, and homozygote for the same variant, respectively. In this report we demonstrated an Alport syndrome family with a novel mutation in COL4A4 gene (c.1856G>A) that has been first reported to our best knowledge.

Clinical and genetic diagnosis of a pedigree affected with autosomal recessive Alport syndrome / 中华医学遗传学杂志

Objective@#To explore the genetic basis of a child with chronic kidney disease featuring renal shrinkage and creatinine increase.@*Methods@#Peripheral venous blood samples were taken from the child, his brother and two parents and subjected to whole exome sequencing. Suspected mutations were verified by Sanger sequencing. Bioinformatic analysis was carried out to predict the influence of mutations on the structure and function of the protein product.@*Results@#High-throughput and Sanger sequencing revealed that the child has carried compound heterozygous mutations of the COL4A4 gene, namely c. 4550T>G in exon 47 (inherited from his mother) and c. 199C>T in exon 5 (inherited from his father). Neither mutation was reported previously. Bioinformatic analysis showed that both mutations have located in highly conserved regions. The same mutations were not found in his brother.@*Conclusion@#The compound heterozygous c. 4550T>G and c. 199C>T mutations probably underlie the disease in this child. The findings have enriched the mutation spectrum of the COL4A4 gene.

Research progress of benign familial hematuria / 中华实用儿科临床杂志

Benign familial hematuria,also called thin basement membrane nephropathy,is caused by a heterozygous mutation in the COL4A3 or COL4A4 gene.The prognosis of the patients with benign familial hematuria,who present isolated hematuria without associated with proteinuria and normal renal function,is good in childhood.However,the prognosis of part of the patients with benign familial hematuria,who appear proteinuria,hypertension,chronic renal failure and end-stage kidney disease,is poor in adulthood.Therefore,the patients with benign familial hematuria should be carried on the long-term follow-up,and may be reviewed every 1-2 years for hypertension,proteinuria,and renal impairment.Treatment for benign familial hematuria should include an angiotensin converting enzyme inhibitor to delay the onset of renal failure.

Diagnosis of a boy with sporadic Alport syndrome using next generation sequencing and literature review / 中华实用儿科临床杂志

Objective To study the feasibility of testing three disease-causing genes for Alport syndrome,COL4A3,COL4A4 and COL4AS,in diagnosing patients with sporadic Alport syndrome by using targeted capture and next generation sequencing.Methods The clinical data of a 9-year-old boy suspected with Alport syndrome were collected.Genomic DNA was extracted using standard procedures from the peripheral blood leukocytes of the patient and his parents,respectively.Targeted capture and next generation sequencing and Sanger sequencing were applied to analyze the mutations in the 3 disease-causing genes.Clinical data of cases reported already with autosomal recessive Alport syndrome caused by the mutations in the COL4A4 gene were summarized.Results The patient was presented with neither family history of hematuria nor chronic renal failure.Haematuria and proteinuria were found at the age of 1 year.The patient presented with episodes of macrohaematuria and gradually developed nephrotic-level proteinuria.At the age of 8 years 7 months,bilateral sensorineural hearing loss was diagnosed.So a probable diagnosis of Alport syndrome was postulated.A compound heterozygous pathogenic mutations of 3578-1G ＞ A and 3967 C ＞ T(Q1323X) were identified in the COL4A4 gene in the patient.The mutation of 3578-1G ＞ A was inherited from his father,and the mutation of Q1323X from his mother.The patient was decisively diagnosed with autosomal recessive Alport syndrome.Conclusions The test of COL4A3,COL4A4 and COL4A5 genes can help diagnose patients with sporadic Alport syndrome by using targeted capture and next generation sequencing.

Identifi cation of novel variants in the COL4A4 gene in Korean patients with thin basement membrane nephropathy.

Background & objectives: The α4 chain of the type 4 collagen family is an important component of the glomerular basement membrane (GBM) in the kidney. It is encoded by the COL4A4 gene, and mutations of this gene are known to be associated with thin basement membrane nephropathy (TBMN). To better understand the contribution of variants in the COL4A4 gene to TBMN, we investigated the sequence of the complete COL4A4 gene in 45 Korean patients with TBMN. Method: Genomic DNA was obtained from the peripheral blood lymphocytes. For the analysis of the COL4A4 gene, all the exons including splicing sites were amplififi ed by PCR and screened by direct sequencing analysis. Results: Eight novel COL4A4 sequence variants were found in these patients. Two of these variants, G199R and G1606E, were possibly pathogenic variants affecting the phenotype. None of these variants were observed in 286 chromosomes from normal Korean control subjects. In addition, 39 polymorphisms including 7 novel SNPs were identifi ed in this study. Interpretation & conclusion: The frequency of COL4A4 mutations in Korean patients with TBMN is low and the other cases may have mutations in other genes like COL4A3. Screening of the COL4A3 gene and fi nding a novel causative gene for TBMN will help clarify the pathogenesis of this disorder and perhaps for distinguishing TBMN from Alport syndrome.