Evidence For Digenic Inheritance Research Articles

P0065DOUBLE MUTATION INHERITANCE IN PATIENTS WITH FOCAL SEGMENTAL GLOMERULOSCLEROSIS AND ALPORT SUNDROME

Abstract Background and Aims Focal segmental glomerulosclerosis (FSGS) and Alport syndrome (AS) are the leading causes of ESRD globally. FSGS and AS are clinically heterogeneous nephropathies and mainly genetic causes are the mutations in genes expressed in podocytes and glomerular basement membrane (GBM) respectively. A simple Mendelian model fail to explain the genetic control of both nephropathies completely because of the heterogeneous nature and presence of incomplete penetrance. Therefore, here we investigated the possible digenic control of FSGS and AS. Method To detect the double mutational (mono- or di-genic) cause of FSGS and AS, we conducted whole exome sequencing (WES) and panel sequencing in 67 kidney patients during the period of four years (2015 to June 2019). Inclusion criteria was the proband's clinical symptoms confirming the FSGS or AS based on clinical symptoms and renal biopsy. Clinical and genetic analyses were implemented to correlate the phenotypes with genotypes. Results Genetic analysis discovered that 35 out of 67 (52.23%) had genetic cause of selected nephropathies and 24 out of 35 (68.57%) had mutations in COL4A (3,4 & 5) genes and 11 (31.42%) in other genes. Interestingly, we found 7 out of 35 patients (20%) with double mutations (mono- or di-genic) in COL4A3/COL4A4 genes. After the mentioned period, during routine genetic screening, we also found another patient having double mutations in COL4A3 gene. Subsequently, Sanger sequencing confirmed that the identified mutations were co-segregating with the disease(s) in an incomplete penetrance fashion within the family. Lastly, we found 16 mutations in 8 patients having either monogenic or digeneic double mutations in COL4A3 and/or COL4A4 genes. In sum, we found 12 (75%) mutations in COL4A3 and 4 in COL4A4 (25%), and5 probands (62.5%) had compound heterozygous mutations in COL4A3, 1 proband (12.5%) had in COL4A4 and 2 probands (25%) had digenic (COL4A3/COL4A4) mutations. Last of all, among all the mutations, 10 were novel and 6 have been described previously. Conclusion This genetic analysis provides the first evidence for digenic inheritance of FSGS. The nephrologists and clinical geneticists should keep this possibility in mind for the accuracy in diagnosis, disease management and genetic counseling in future. Additionally, we are also adding 10 novel mutations in COL4A3 and COL4A4 genetic pools.

Distal renal tubular acidosis in a Libyan patient: Evidence for digenic inheritance

Aim of the studyRecent advances in understanding the underlying molecular mechanism for distal renal tubular acidosis (dRTA), led to an increased attention towards the primary and the familial forms of the disease. Mutations in ATP6V1B1 and ATP6V0A4 are usually responsible for the recessive form of the disease. Mutations in gene AE1 encoding the Cl-/HCO3- exchanger, usually present as dominant dRTA, but a recessive pattern has been recently described. Our objective is to identify the mutational spectrum responsible of dRTA in a consanguineous Libyan family. Materials and methodsBoth ATP6V0A4 and ATP6V1B1 genes were preferentially screened in our patient. Additional whole exome sequencing (WES) in the same patient, offered a wider view on potential chromosomal rearrangements as well as the mutational spectrum of other genes involved in this disease. ResultsThe patient is a heterozygote for two different mutations, one in each of the genes ATP6V0A4 and ATP6V1B1, while no deleterious variation was detected in the remaining genes responsible for the recessive form of dRTA. Homozygosity mapping and WES confirmed our findings and supported the hypothesis of a digenic inheritance model existing as an explanation for dRTA. ConclusionsTo our knowledge, this is the first report describing a Libyan patient with dRTA who suffered from early-onset sensorineural hearing loss, with a digenic mode of inheritance, supported by the identification of two novel mutations. This study increases the understanding of how dRTA is genetically transmitted, while offers a good outline towards the molecular diagnostics and genetic counseling for dRTA in Lybians.

Evidence of digenic inheritance in autoinflammation-associated genes.

Familial Mediterranean fever (FMF) has traditionally been considered as a monogenic autosomal recessive disorder caused by mutations in the MEFV gene with highest incidence among Mediterranean populations. In a considerable number of patients with typical FMF, only one MEFV mutation was identified and the possibility that more than one autoinflammatory gene may be responsible for their disease was investigated. In the present study, an extensive search for possible mutations in three hereditary recurrent fever (HRF) genes was performed in 128 MEFV heterozygous Greek-Cypriots clinically diagnosed based on their phenotype with FMF-like disease from a previous study. Sequence analysis was performed for MVK, TNFRSF1A and NLRP3 genes which is also known to cause HRFs. In total, three patients were identified with heterozygous mutations and a second mutation in an autoinflammatory gene. Two patients carried a MEFV mutation and a NLRP3 mutation, and an additional third carried a MEFV mutation and a TNFRSF1A mutation. Patient 1 carried MEFV p.[Val726Ala] (NM_000243.2:c.2177T>C) and NLRP3 p.[Val198Met] (NM_001243133.1:c.592G>A) variants and patient 2 carried MEFV p.[Glu148Gln] (NM_000243.2:c.442G>C) variant which is of uncertain significance and NLRP3 p.[Arg176Trp] (NM_001243133.1:c.526C>T). Lastly, patient 3 was identified to carry MEFV p.[Met694Val] (NM_000243.2:c.2080A>G) and TNFRSF1A p.[Arg121Gln] (NM_001065.3:c.362G>A) variants. The results from this study indicate that screening of genes known to cause HRFs in patients already identified with a single MEFV mutation, can reveal quite rare but potentially causative mutational combinations at different loci. Such interaction provide further evidence for possible locus-locus interactions and phenotypes resulting from digenic inheritance.

Evidence of digenic inheritance in Alport syndrome

BackgroundAlport syndrome is a clinically heterogeneous, progressive nephropathy caused by mutations in collagen IV genes, namely COL4A3 and COL4A4 on chromosome 2 and COL4A5 on chromosome X. The wide phenotypic...

First evidence for digenic inheritance in hereditary colorectal cancer by mutations in the base excision repair genes

Biallelic mutations in the base excision repair gene Mut Y homologue ( MUTYH) are responsible for variable recessively inherited phenotypes of polyposis. Beside MUTYH, the proteins 8-oxo-guanine DNA glycosylase ( OGG1) and MTH1 (or NUDT1) are also involved in the repair of 7,8-dihydro-8-oxoguanine (8-oxo-G), previous studies, however, only found missense mutations of unclear pathogenicity in either MTH1 or OGG1. To investigate the role of a defective 8-oxo-G repair we performed a germline mutation screening in the genes OGG1, MTH1 and MUTYH, in 81 patients with a clinical phenotype ranging from attenuated or atypical adenomatous polyposis coli including hyperplastic polyps to hereditary non-polyposis colorectal cancer (HNPCC) type X syndrome without mono- or biallelic mutations in either APC, MUTYH or the DNA mismatch repair genes. We describe here the first pathogenic germline mutation in OGG1, a splice site mutation affecting exon 1, which was inherited from the father, in combination with a maternal MUTYH missense mutation p.Ile223Val in a female patient with advanced synchronous colon cancer and adenomas at the age of 36 years pointing towards digenic inheritance for colorectal cancer (CRC) predisposition. Monoallelic missense mutations in MTH1 (3x), OGG1 (2x), or MUTYH (3x) were identified in 10 patients (12%), three of them were novel. Our findings indicate that mutations in other genes of the 8-oxo-G repair beside MUTYH are involved in CRC predisposition. Oligogenic inheritance affecting genes of a certain repair pathway might therefore be the missing link between monogenic and polygenic traits.

Evidence for digenic inheritance in a family with both febrile convulsions and temporal lobe epilepsy implicating chromosomes 18qter and 1q25-q31.

We report a clinical and genetic study of a French family among whom febrile convulsions (FC) are associated with subsequent temporal lobe epilepsy (TLE) in the same individual, without magnetic resonance imaging-identifiable hippocampal abnormalities. Linkage analyses excluded the loci FEB1 and FEB2, previously implicated in FC; the GEFS+1 locus responsible for generalized epilepsy with febrile seizures plus; and the locus implicated in lateral temporal lobe epilepsy. After scanning the entire genome, significant lod scores (>3) for markers on 18qter and suggestive lod scores (>2) for markers on 1q25-q31 were obtained. An analysis of the haplotypes at these two loci supported the hypothesis that two genes segregated with the phenotype. All patients shared common haplotypes for both 1q25-q31 and 18qter chromosomes. All but one unaffected at-risk individuals carried only one, or none, of the disease haplotypes. Under the assumption of digenic inheritance, haplotype reconstruction defined a 26 cM interval on chromosome 1 and a 10 cM interval on chromosome 18. This family suggests that the association between FC and TLE may be observed in the absence of hippocampal structural abnormalities and that they may have, in some cases, a common genetic basis.

Evidence for digenic inheritance in some cases of Antley-Bixler syndrome?

The Antley-Bixler syndrome has been thought to be caused by an autosomal recessive gene. However, patients with this phenotype have been reported with a new dominant mutation at theFGFR2 locus...