Heterozygous deleterious MUTYH variants as a driver for tumorigenesis

MUTYH is a glycosylase involved in the base excision repair of the DNA. Biallelic mutations in the MUTYH gene cause the autosomal recessive condition known as MUTYH‐associated adenomatous polyposis and increase colorectal cancer risk. However, the cancer risk associated with germline variants in individuals carrying only one MUTYH defective allele is controversial and based on studies involving few samples. Here, we described a comprehensive investigation of monoallelic deleterious MUTYH carriers among approximately 10,400 patients across 33 different tumor types and more than 117 thousand samples of normal individuals. Our results indicate MUTYH deficiency in heterozygosity can lead to tumorigenesis through a mechanism of Loss Of Heterozygosity (LOH) of the functional MUTYH allele. We confirmed that the frequency of damaging MUTYH monoallelic variant carriers is higher in individuals with cancer than in the general population, though its frequency is not homogeneous among tumor types. We also demonstrate that MUTYH related mutational signature is elevated only in those patients with loss of the functional allele. We also find that MUTYH characteristic base substitution (C>A) increases stop codon generation and we identify key genes affected during tumorigenesis. In conclusion, we propose that deleterious germline monoallelic MUTYH variant carriers are at a higher risk of developing tumors, specially those types with frequent LOH events, such as adrenal adenocarcinoma.

Defective Allele of the Neuronal Nitric Oxide Synthase Gene Increases Insulin Resistance During Acute Phase of Myocardial Infarction.

Background: glycemia disorders are a strong predictor of mortality in ST-Elevation Myocardial Infarction (STEMI) patients. Disruption in nitric oxide (NO) production is associated with insulin-resistant states. We evaluated whether NO production in carriers of a defective allele of the neuronal nitric oxide synthase (nNOS or NOS1), whose in vivo expression is reduced by up to 50%, might influence the insulin response during acute phase of STEMI. Methods and Results: Consecutive patients with STEMI (n = 354) underwent clinical evaluations and genotyping for the promoter variation rs41279104. Blood tests were performed at admission (D1) and after five days (D5) of in-hospital follow up, with the disposition index assessed in the period. Flow-mediated dilation (FMD) was assessed by reactive hyperemia on the 30th day. Homozygotes for the defective allele (A) showed lower glycemia and insulin sensitivity at D1 while showing the highest b-cells function and no changes in the circulating NO pool, what is compatible with hyperresponsive b-cells to counteract the inherent glucose-resistant state of AA patients. At D5, glycemic scores shifted to indicate greater insulin sensitivity among A homozygotes, paralleled by a slight yet poor increase in NO bioavailability than that among G carriers. All in all, defective homozygotes showed greater insulin resistance expressed by the disposition index at admission, which was compensated 5 days after STEMI even though FMD of A carriers was lower compared to G homozygotes. Conclusion: a defective nNOS allele seems to elicit endocrine adaptation and to associate with insulin resistance during the acute phase of STEMI.

Loss of FAS1 function reveals rescue of an aberrant intra-S-phase checkpoint by the G2/M checkpoint regulator SOG11[OPEN]

ABSTRACTThe WEE1 and ATR kinases represent important regulators of the plant intra-S-phase checkpoint, as evidenced by the hypersensitivity of WEE1KO and ATRKO roots to replication inhibitory drugs. Here, we report on the identification of a defective allele of the FASCIATA1 (FAS1) subunit of the chromatin assembly factor 1 (CAF-1) complex as a suppressor of WEE1- or ATR-deficient plants. We demonstrate that lack of FAS1 activity results in the activation of an ATM- and SOG1-mediated G2/M-arrest that makes the ATR and WEE1 checkpoint regulators redundant. This ATM activation accounts for telomere erosion and loss of ribosomal DNA described for the fas1 plants. Knocking out SOG1 in the fas1 wee1 background restores replication stress sensitivity, demonstrating that SOG1 plays a prominent role as secondary checkpoint regulator in plants that fail to activate the intra-S-phase checkpoint.One-Sentence SummaryLack of the chromatin assembly factor-1 subunit FAS1 results in a DNA damage response that overrules the need for replication checkpoint activators.

Digenic mutations in ALDH2 and ADH5 impair formaldehyde clearance and cause a multisystem disorder, AMeD syndrome

Rs671 in the aldehyde dehydrogenase 2 gene (ALDH2) is the cause of Asian alcohol flushing response after drinking. ALDH2 detoxifies endogenous aldehydes, which are the major source of DNA damage repaired by the Fanconi anemia pathway. Here, we show that the rs671 defective allele in combination with mutations in the alcohol dehydrogenase 5 gene, which encodes formaldehyde dehydrogenase (ADH5FDH), causes a previously unidentified disorder, AMeD (aplastic anemia, mental retardation, and dwarfism) syndrome. Cellular studies revealed that a decrease in the formaldehyde tolerance underlies a loss of differentiation and proliferation capacity of hematopoietic stem cells. Moreover, Adh5−/−Aldh2E506K/E506K double-deficient mice recapitulated key clinical features of AMeDS, showing short life span, dwarfism, and hematopoietic failure. Collectively, our results suggest that the combined deficiency of formaldehyde clearance mechanisms leads to the complex clinical features due to overload of formaldehyde-induced DNA damage, thereby saturation of DNA repair processes.

Arabidopsis Sucrose Transporter AtSuc1 introns act as strong enhancers of expression

The expression of AtSUC1 is controlled by the promoter and intragenic sequences. AtSUC1 is expressed in roots, pollen and trichomes. However, AtSUC1 promoter-GUS transgenics only show expression in trichomes and pollen. Here, we show that the root expression of AtSUC1 is controlled by an interaction between the AtSUC1 promoter and two short introns. The deletion of either intron from whole-gene-GUS constructs results in no root expression, showing that both introns are required. The two introns in tandem, fused to GUS, produce high constitutive expression throughout the vegetative parts of the plant. When combined with the promoter, the expression driven by the introns is reduced and localized to the roots. In Arabidopsis seedlings, exogenously applied sucrose induces the expression of AtSUC1 in roots and causes anthocyanin accumulation. atsuc1 loss-of-function mutants are defective in sucrose-induced anthocyanin accumulation. We show that an AtSUC1 whole-gene-GUS construct expressing a nonfunctional AtSUC1 (D152N) mutant, that is transport inactive, is defective in sucrose-induced AtSUC1 expression when expressed in an atsuc1-null background. We also show that the transport-defective allele does not complement the loss of sucrose-induced anthocyanin accumulation in null atsuc1 mutants. The results indicate that sucrose uptake via AtSUC1 is required for sucrose-induced AtSUC1 expression and sucrose-induced anthocyanin accumulation and that the site for sucrose detection is intracellular.

Comparison of αLEPRA and αLELY Co-Inheritance with a SPTA1 Whole Gene Deletion, a Family Study

Background: Genetic variants resulting in quantitative defects in the production of α-spectrin are associated with autosomal recessive hereditary spherocytosis (HS). Because erythroid cells produce α-spectrin in a 3-4:1 ratio in relation to β-spectrin, one defective allele is typically well-tolerated and a single null allele combined with a second partially defective allele may display a sub-clinical phenotype. Protein expression can be reduced by nonsense, frameshift, missense or splicing variants but reported large deletion events are extraordinarily rare (n = 1). Splicing variants include the low expression alleles αLELY - Low Expression LYon (SPTA1:c.6531-12C>T, p.?) and αLEPRA-Low Expression PRAgue (SPTA1:c.4339-99C>T, p.?) which reduce protein expression by 50% and 16%, respectively. Here, we present a family study with a whole gene SPTA1 deletion that characterizes the patient phenotype when a full gene mutation is co-inherited with the αLEPRA and αLELY low expression alleles. Methods: The 6 month-old male proband had a history of congenital Coombs negative hemolytic anemia requiring transfusion from 3 months of age and in whom a red cell membrane disorder was clinically suspected. Pretransfusion CBC and peripheral blood smear results were unknown. Transfused CBC indices were as follows: RBC 4 x 1012/L, HGB 11 g/dL, MCV 76 fL, MCH 27 pg, MCHC 36 g/dL and a reticulocyte count of 1.8%. The proband's mother, of Cuban descent, and father, of European descent, had no history of anemia or HS. Targeted high throughput sequencing of genes related to hereditary hemolytic anemia was performed for the detection of single nucleotide variants (SNVs) and small insertion/deletion variants (indels). Relative quantitative real time PCR (RT-PCR) was utilized to confirm large structural variants. Results: Sequencing identified a large heterozygous deletion that spanned the entire SPTA1 gene (NC_000001.11:g.(?_158656337)_(158581024_?) in the proband and his mother. In addition, the proband had inherited hemizygous αLEPRA from his father. The mother had hemizgous αLELY. The father showed heterozygous αLEPRA and no other SPTA1 variants (Table 1). Conclusion: To our knowledge, only Iolascon et al in 2011 has reported a SPTA1 gene large deletion (SpectrinExeter, exon 11-exon 12 deletion, loss of 83 amino acids) which resulted in a structurally abnormal protein and ellipto-poikilocytosis phenotype when in trans to αLELY. Our current case is the first reported SPTA1 full gene deletion and our family study allows comparison of the effects of coinheritance of the low expression alleles αLEPRA and αLELY. When in combination with complete absence of the SPTA1 gene in trans configuration, αLELY manifests in subclinical effects and αLEPRA causes a recessive HS phenotype, which resulted in severe anemia. This contrast further demonstrates that, unlike αLEPRA, αLELY does not decrease the α-spectrin concentration sufficiently to contribute to the baseline phenotype regardless of the severity of the second allele mutation for quantitative disorders such as HS. Disclosures No relevant conflicts of interest to declare.

A Simplified Technique for Evaluating Human CCR5 Genetic Polymorphism

To involve students in thinking about the problem of AIDS (which is important in the view of nondecreasing infection rates), we established a practical lab using a simplified adaptation of Thomas’s (2004) method to determine the polymorphism of HIV co-receptor CCR5 from students’ own epithelial cells. CCR5 is a receptor involved in inflammatory processes, which has been misused by some pathogens, including HIV, to enter host cells. As a result, a defective allele CCR5-Δ32 has been enriched in some populations. The interesting story and hands-on work with their own tissue absorbed students in this 2-hour practical.