Cubilin Gene Research Articles

Polymorphisms in LRP2 and CUBN genes and their association with serum vitamin D levels and sleep apnea

PurposeVitamin D deficiency has been associated with the occurrence of obstructive sleep apnea syndrome (OSAS). Megalin (LRP2) and cubilin (CUBN) are implicated in vitamin D metabolism, whereas LRP2 and CUBN polymorphisms have been previously associated with variable serum vitamin D levels. The present study aimed to evaluate the role of LRP2 rs2228171 c.8614C > T and CUBN rs1801222 c.758A > G polymorphisms in OSAS susceptibility, independently or in synergy with vitamin D levels.MethodsVitamin D serum concentration of consecutive individuals was measured. PCR–RFLP was used for LRP2 rs2228171 and CUBN rs1801222 genotyping.ResultsA total of 176 individuals was enrolled, including 144 patients with OSAS and 32 controls. Frequency of LRP2 rs2228171 c.8614 T and CUBN rs1801222 c.758G alleles was estimated at 22.4% and 79.8%, respectively. LRP2 and CUBN polymorphisms were not associated with OSAS occurrence (rs2228171Τ allele: 22.9% in OSAS group vs. 20.3% in controls, p = 0.651; rs1801222A allele 19.4% in OSAS group vs. 23.4% in controls, p = 0.471). Frequency of CUBN rs1801222A allele carriers was increased in patients with moderate or severe OSAS compared to mild OSAS (p = 0.028). Patients with OSAS homozygous for LRP2 CC and CUBN GG genotypes had lower vitamin D serum concentration compared to controls carrying the same genotype (18.0 vs 27.0 ng/mL, p = 0.006 and 19.0 vs 27.5 ng/mL, p = 0.007, respectively).ConclusionCUBN rs1801222 polymorphism may affect OSAS severity. Among other factors, low vitamin D concentration is associated with OSAS occurrence, irrespectively of LRP2 and CUBN polymorphisms.

Imerslund-Grasbeck syndrome- a rare cause of megaloblastic anemia in an infant with homozygous mutation in CUBN gene: a case report and review of the literature

Megaloblastic anaemia is one of the important causes of pancytopenia in children and nutritional deficiencies of vitamin B12 and folate are the most common causes comprising 95% of these cases. Defects in absorption, transport and metabolism of vitamin B12 are well described, however, are very rare. We report a rare case of Imersland Grasbeck syndrome, in an infant who presented with pancytopenia, with defective absorption of B12-intrinsic factor complex at the ileum and defective tubular reabsorption of proteins in renal tubule due to same protein defect caused by mutations in two genes – CUBN (cubilin) and AMN (amnionless).

Genetic Variability in the Iron Homeostasis Pathway and Patient Outcomes After Aneurysmal Subarachnoid Hemorrhage.

Iron can be detrimental to most tissues both in excess and in deficiency. The brain in particular is highly susceptible to the consequences of excessive iron, especially during blood brain barrier disruption after injury. Preliminary evidence suggests that iron homeostasis is important during recovery after neurologic injury; therefore, the exploration of genetic variability in genes involved in iron homeostasis is an important area of patient outcomes research. The purpose of this study was to examine the relationship between tagging single nucleotide polymorphisms (SNPs) in candidate genes related to iron homeostasis and acute and long-term patient outcomes after aneurysmal subarachnoid hemorrhage (aSAH). This study was a longitudinal, observational, candidate gene association study of participants with aSAH that used a two-tier design including tier 1 (discovery, n = 197) and tier 2 (replication, n = 277). Participants were followed during the acute outcome phase for development of cerebral vasospasm and delayed cerebral ischemia (DCI) and during the long-term outcome phase for death and gross functional outcome using the Glasgow Outcome Scale (GOS; poor = 1-3). Genetic association analyses were performed using a logistic regression model adjusted for age, sex, and Fisher grade. Approximate Bayes factors (ABF) and Bayesian false discovery probabilities (BFDP) were used to prioritize and interpret results. In tier 1, 235 tagging SNPs in 28 candidate genes were available for analysis and 26 associations (20 unique SNPs in 12 genes) were nominated for replication in tier 2. In tier 2, we observed an increase in evidence of association for three associations in the ceruloplasmin (CP) and cubilin (CUBN) genes. We observed an association of rs17838831 (CP) with GOS at 3months (tier 2 results, odds ratio [OR] = 2.10, 95% confidence interval [CI] = 1.14-3.86, p = 0.018, ABF = 0.52, and BFDP = 70.8%) and GOS at 12months (tier 2 results, OR = 1.86, 95% CI 0.98-3.52, p = 0.058, ABF = 0.72, and BFDP = 77.3%) as well as rs10904850 (CUBN) with DCI (tier 2 results, OR = 0.70, 95% CI 0.48-1.02, p = 0.064, ABF = 0.59, and BFDP = 71.8%). Among the genes examined, our findings support a role for CP and CUBN in patient outcomes after aSAH. In an effort to translate these findings into clinical utility and improve outcomes after aSAH, additional research is needed to examine the functional roles of these genes after aSAH.

CUBN variants uncouple proteinuria from kidney function.

A new study links pathogenic cubilin gene (CUBN) variants to proteinuria without progressive renal impairment, providing reassurance for a subset of patients, calling into question the accepted pathogenesis of glomerulosclerosis and suggesting future therapeutic options.

Not all proteinuria is created equal.

Albuminuria acts as a marker of progressive chronic kidney disease and as an indicator for initiation of hypertension treatment via modulation of the renin-angiotensin-aldosterone system with angiotensin receptor blockers or angiotensin-converting enzyme inhibitors. However, the true significance of albuminuria has yet to be fully defined. Is it merely a marker of underlying pathophysiology, or does it play a causal role in the progression of kidney disease? The answer remains under debate. In this issue of the JCI, Bedin et al. used next-generation sequencing data to identify patients with chronic proteinuria who had biallelic variants in the cubilin gene (CUBN). Through investigation of these pathogenic mutations in CUBN, the authors have further illuminated the clinical implications of albuminuria.

Maternal gastric intrinsic factor A68G and paternal cubilin C758T variants increase the risk for neural tube defects in the fetus: A family-triad study from South India

BackgroundNeural tube defects (NTDs) are the leading cause of infant deaths worldwide. Gastric Intrinsic Factor (GIF) and Cubilin (CUBN) genes essential for early fetal development have not been extensively studied in NTDs. In view of this, present study aimed to evaluate association of GIF A68G and CUBN C758T variants with NTD risk using family-based triad approach. MethodsA total of 924 subjects including 124 NTD case-parent trios and 184 healthy control-parent trios diagnosed at Institute of Genetics and Hospital for Genetic Diseases, Hyderabad were considered for the study. Blood samples from study group parents and umbilical cord tissue samples from NTD cases and controls were genotyped for GIF A68G (rs35211634) and CUBN C758T (rs1801222) variants for their association with NTDs. Serum holo-transcobalamin (holo-TC) levels were measured using ELISA. ResultsAssessment of maternal-paternal genotype incompatibility risk for NTD revealed maternal AG genotype in combination with paternal AA genotype of GIF A68G (AGxAA = AG,OR = 2.92,p = .006) and maternal CC genotype with paternal CT genotype combination of CUBN C758T (CCxCT = CT,OR = 3.71,p < .001) significantly increased the risk for NTDs. Allelic gene-gene interactions of GIF A68G and CUBN C758T showed significant association of maternal G-C (OR = 6.34,p < .001) and paternal A-T alleles (OR = 2.61,p = .001) for the occurrence of NTDs. Further, parent-of-origin effects also revealed significant transmission of maternal ‘G’ allele (OR = 3.50,p = .015) and paternal ‘T' allele (OR = 2.57,p = .016) to NTDs. Correlation of serum holo-TC levels with GIF A68G and CUBN C758T genotypes revealed significant association of paternal CT genotype of C758T variant with decreased holo-TC levels compared to controls (p = .013). However, GIF A68G variant showed no significant association with holo-TC levels. ConclusionThe present family-based triad study provides the first report on the risk of NTD susceptibility being potentially influenced by maternal GIF A68G and paternal CUBN C758T variants.

Polymorphisms in the vitamin D system and mortality – The Tromsø study

Vitamin D deficiency is associated with diabetes, cancer, immunological and cardiovascular diseases as well as increased mortality. It has, however, been difficult to show a causal relation in randomized, controlled trials. Mendelian randomization studies provide another option for testing causality, and results indicate relations between the serum 25-hydroxyvitamin D (25(OH)D) level and some diseases, including mortality. We have from the Tromsø Study in 2012 published non-significant relations been vitamin D related single nucleotide polymorphisms (SNPs) and mortality, but have since then genotyped additional subjects, the observation time is longer and new SNPs have been included. For the present study genotyping was performed for SNPs in the NADSYN1, CYP2R1, GC and CYP24A1, VDR, CUBILIN and MEGALIN genes in 11 897 subjects who participated in the fourth survey of the Tromsø Study in 1994–1995. Serum 25(OH)D levels were measured in 6733 of these subjects. Genetic scores based on SNPs related to the serum 25(OH)D level (NADSYN1 and CYP2R1 SNPs (synthesis score) and GC and CYP24A1 SNPs (metabolism score)) and serum 25(OH)D percentile groups were created. Mortality data was updated till end of March 2017 and survival analysed with Cox regression adjusted for sex and age. During the observation period 5491 subjects died. The 25(OH)D synthesis (but not the metabolism) genetic score and the serum 25(OH)D percentile groups were (without Bonferroni correction) significantly related to mortality in favour of high serum 25(OH)D. None of the SNPs in the VDR or MEGALIN genes were related to mortality. However, for the rs12766939 in the CUBILIN gene with the major homozygote as reference, the hazard ratio for mortality for the minor homozygote genotype was 1.17 (1.06–1.29), P < 0.002. This should be viewed with caution, as rs12766939 was not in Hardy-Weinberg equilibrium. In conclusion, our study confirms a probable causal but weak relation between serum 25(OH)D level and mortality. The relation between rs12766939 and mortality needs confirmation in more homogenous cohorts.

Albumin uptake in human podocytes: a possible role for the cubilin-amnionless (CUBAM) complex

Albumin re-uptake is a receptor-mediated pathway located in renal proximal tubuli. There is increasing evidence of glomerular protein handling by podocytes, but little is known about the mechanism behind this process. In this study, we found that human podocytes in vitro are committed to internalizing albumin through a receptor-mediated mechanism even after exposure to low doses of albumin. We show that these cells express cubilin, megalin, ClC-5, amnionless and Dab2, which are partners in the tubular machinery. Exposing human podocytes to albumin overload prompted an increase in CUBILIN, AMNIONLESS and CLCN5 gene expression. Inhibiting cubilin led to a reduction in albumin uptake, highlighting its importance in this mechanism. We demonstrated that human podocytes are committed to performing endocytosis via a receptor-mediated mechanism even in the presence of low doses of albumin. We also disclosed that protein overload first acts on the expression of the cubilin-amnionless (CUBAM) complex in these cells, then involves the ClC-5 channel, providing the first evidence for a possible role of the CUBAM complex in albumin endocytosis in human podocytes.

Association Analysis of the Cubilin (CUBN) and Megalin (LRP2) Genes with ESRD in African Americans.

Genetic variation in the cubilin (CUBN) gene is associated with albuminuria and CKD. Common and rare coding variants in CUBN and the gene encoding its transport partner megalin (LRP2) were assessed for association with ESRD in blacks. Sixty-six CUBN and LRP2 single-nucleotide polymorphisms (SNPs) were selected and analyzed in this multistage study. Exome sequencing data from 529 blacks with type 2 diabetes (T2D) -associated ESRD and 535 controls lacking T2D or nephropathy (the Type 2 Diabetes Genes [T2D-GENES] Consortium) were first evaluated, focusing on coding variants in CUBN and LRP2; 15 potentially associated SNPs identified from the T2D-GENES Consortium as well as 51 other selected SNPs were then assessed in an independent T2D-ESRD sample set of blacks (the Affymetrix Axiom Biobank Genotyping Array [AXIOM]; 2041 patients with T2D-ESRD, 627 patients with T2D without nephropathy, and 1140 nondiabetic, non-nephropathy controls). A meta-analysis combining the T2D-GENES Consortium and the AXIOM data was performed for 18 overlapping SNPs. Additionally, all 66 SNPs were genotyped in the Wake Forest School of Medicine samples of blacks with nondiabetic ESRD (885 patients with nondiabetic ESRD and 721 controls). Association testing with ESRD was performed in models including age, sex, African ancestry proportion, and apolipoprotein L1 gene renal-risk variants. CUBN SNP rs1801239 (I2984V), previously associated with albuminuria, was significantly associated with T2D-ESRD in blacks (the T2D-GENES Consortium and the AXIOM meta-analysis, P=0.03; odds ratio, 1.31; 95% confidence interval, 1.03 to 1.67; minor allele frequency =0.028). A novel LRP2 missense variant, rs17848169 (N2632D), was also significantly protective from T2D-ESRD (the T2D-GENES Consortium and the AXIOM, P<0.002; odds ratio, 0.47; 95% confidence interval, 0.29 to 0.75; meta-analysis minor allele frequency =0.007). Neither SNP was associated with T2D when contrasting patients with T2D with controls lacking diabetes. CUBN and LRP2 SNPs were not associated with nondiabetic etiologies of ESRD. Evidence for genetic association exists between a cubilin and a rare megalin variant with diabetes-associated ESRD in populations with recent African ancestry.

A Genetic Variant in Vitamin B12 Metabolic Genes That Reduces the Risk of Congenital Heart Disease in Han Chinese Populations

BackgroundGenome-wide association studies on components of the one-carbon metabolic pathway revealed that human vitamin B12 levels could be significantly influenced by variationsinthefucosyltransferase 2 (FUT2), cubilin (CUBN), and transcobalamin-I (TCN1) genes. An altered vitamin B12 level is an important factor that disturbs the homeostasis of the folate metabolism pathway, which in turn can potentially lead to the development of congenital heart disease (CHD). Therefore, we investigated the association between the variants of vitamin B12-related genes and CHD in Han Chinese populations.Methods and ResultsSix variants of the vitamin B12-related genes were selected for analysis in two independent case-control studies, with a total of 868 CHD patients and 931 controls. The variant rs11254363 of the CUBN gene was associated with a decreased risk of developing CHD in both the separate and combined case-control studies. Combined samples from the two cohorts had a significant decrease in CHD risk for the G allele (OR = 0.48, P = 1.7×10−5) and AG+GG genotypes (OR = 0.49, P = 4×10−5), compared with the wild-type A allele and AA genotype, respectively.ConclusionsConsidering the G allele of variant rs11254363 of the CUBN gene was associated with an increased level of circulating vitamin B12. This result suggested that the carriers of the G allele would benefit from the protection offered by the high vitamin B12 concentration during critical heart development stages. This finding shed light on the unexpected role of CUBN in CHD development and highlighted the interplay of diet, genetics, and human birth defects.

Degenerative Liver Disease in Young Beagles with Hereditary Cobalamin Malabsorption Because of a Mutation in the Cubilin Gene

Degenerative Liver Disease in Young Beagles with Hereditary Cobalamin Malabsorption Because of a Mutation in the Cubilin Gene

Cubilin Maintains Blood Levels of HDL and Albumin

Cubilin is an endocytic receptor highly expressed in renal proximal tubules, where it mediates uptake of albumin and filtered forms of apoA-I/HDL. Cubilin deficiency leads to urinary loss of albumin and apoA-I; however, the consequences of cubilin loss on the homeostasis of blood albumin and apoA-I/HDL have not been studied. Using mice heterozygous for cubilin gene deletion (cubilin HT mice), we show that cubilin haploinsufficiency leads to reduced renal proximal tubular uptake of albumin and apoA-I and significantly increased urinary loss of albumin and apoA-I. Moreover, cubilin HT mice displayed significantly decreased blood levels of albumin, apoA-I, and HDL. The levels of albumin and apoA-I protein or mRNA expressed in the liver, kidney, or intestine of cubilin HT mice did not change significantly. The clearance rate of small HDL3 particles (density>1.13 g/ml) from the blood increased significantly in cubilin HT mice. In contrast, the rate of clearance of larger HDL2 particles from the blood did not change significantly, indicating a decreased half-life for HDL particles capable of filtering through the glomerulus. On the basis of these findings, we conclude that cubilin deficiency reduces renal salvage and delivery back to the blood of albumin and apoA-I, which decreases blood levels of albumin and apoA-I/HDL. These findings raise the possibility that therapeutic increase of renal cubilin expression might reduce proteinuria and increase blood levels of albumin and HDL.

A frameshift mutation in the cubilin gene (CUBN) in Beagles with Imerslund-Gräsbeck syndrome (selective cobalamin malabsorption)

Mammals are unable to synthesize cobalamin or vitamin B12 and rely on the uptake of dietary cobalamin. The cubam receptor expressed on the intestinal endothelium is required for the uptake of cobalamin from the gut. Cubam is composed of two protein subunits, amnionless and cubilin, which are encoded by the AMN and CUBN genes respectively. Loss-of-function mutations in either the AMN or the CUBN gene lead to hereditary selective cobalamin malabsorption or Imerslund-Gräsbeck syndrome (IGS). We investigated Beagles with IGS and resequenced the whole genome of one affected Beagle at 15× coverage. The analysis of the AMN and CUBN candidate genes revealed a homozygous deletion of a single cytosine in exon 8 of the CUBN gene (c.786delC). This deletion leads to a frameshift and early premature stop codon (p.Asp262Glufs*47) and is, thus, predicted to represent a complete loss-of-function allele. We tested three IGS-affected and 89 control Beagles and found perfect association between the IGS phenotype and the CUBN:c.786delC variant. Given the known role of cubilin in cobalamin transport, which has been firmly established in humans and dogs, our data strongly suggest that the CUBN:c.786delC variant is causing IGS in the investigated Beagles.

A Frameshift Mutation in the Cubilin Gene (CUBN) in Border Collies with Imerslund-Gräsbeck Syndrome (Selective Cobalamin Malabsorption)

Imerslund-Gräsbeck syndrome (IGS) or selective cobalamin malabsorption has been described in humans and dogs. IGS occurs in Border Collies and is inherited as a monogenic autosomal recessive trait in this breed. Using 7 IGS cases and 7 non-affected controls we mapped the causative mutation by genome-wide association and homozygosity mapping to a 3.53 Mb interval on chromosome 2. We re-sequenced the genome of one affected dog at ∼10× coverage and detected 17 non-synonymous variants in the critical interval. Two of these non-synonymous variants were in the cubilin gene (CUBN), which is known to play an essential role in cobalamin uptake from the ileum. We tested these two CUBN variants for association with IGS in larger cohorts of dogs and found that only one of them was perfectly associated with the phenotype. This variant, a single base pair deletion (c.8392delC), is predicted to cause a frameshift and premature stop codon in the CUBN gene. The resulting mutant open reading frame is 821 codons shorter than the wildtype open reading frame (p.Q2798Rfs*3). Interestingly, we observed an additional nonsense mutation in the MRC1 gene encoding the mannose receptor, C type 1, which was in perfect linkage disequilibrium with the CUBN frameshift mutation. Based on our genetic data and the known role of CUBN for cobalamin uptake we conclude that the identified CUBN frameshift mutation is most likely causative for IGS in Border Collies.

Phylogenetic analysis of cubilin (CUBN) gene.

Cubilin, (CUBN; also known as intrinsic factor-cobalamin receptor [Homo sapiens Entrez Pubmed ref NM_001081.3; NG_008967.1; GI: 119606627]), located in the epithelium of intestine and kidney acts as a receptor for intrinsic factor – vitamin B12 complexes. Mutations in CUBN may play a role in autosomal recessive megaloblastic anemia. The current study investigated the possible role of CUBN in evolution using phylogenetic testing. A total of 588 BLAST hits were found for the cubilin query sequence and these hits showed putative conserved domain, CUB superfamily (as on 27th Nov 2012). A first-pass phylogenetic tree was constructed to identify the taxa which most often contained the CUBN sequences. Following this, we narrowed down the search by manually deleting sequences which were not CUBN. A repeat phylogenetic analysis of 25 taxa was performed using PhyML, RAxML and TreeDyn softwares to confirm that CUBN is a conserved protein emphasizing its importance as an extracellular domain and being present in proteins mostly known to be involved in development in many chordate taxa but not found in prokaryotes, plants and yeast.. No horizontal gene transfers have been found between different taxa.

Linkage disequilibrium analysis reveals an albuminuria risk haplotype containing three missense mutations in the cubilin gene with striking differences among European and African ancestry populations

BackgroundA recent meta-analysis described a variant (p.Ile2984Val) in the cubilin gene (CUBN) that is associated with levels of albuminuria in the general population and in diabetics.MethodsWe implemented a Linkage Disequilibrium (LD) search with data from the 1000 Genomes Project, on African and European population genomic sequences.ResultsWe found that the p.Ile2984Val variation is part of a larger haplotype in European populations and it is almost absent in west Africans. This haplotype contains 19 single nucleotide polymorphisms (SNPs) in very high LD, three of which are missense mutations (p.Leu2153Phe, p.Ile2984Val, p.Glu3002Gly), and two have not been previously reported. Notably, this European haplotype is absent in west African populations, and the frequency of each individual polymorphism differs significantly in Africans.ConclusionsGenotyping of these variants in existing African origin sample sets coupled to measurements of urine albumin excretion levels should reveal which is the most likely functional candidate for albuminuria risk. The unique haplotypic structure of CUBN in different populations may leverage the effort to identify the functional variant and to shed light on evolution of the CUBN gene locus.

CUBN as a Novel Locus for End-Stage Renal Disease: Insights from Renal Transplantation

Chronic kidney disease (CKD) is a complex disorder. As genome-wide association studies identified cubilin gene CUBN as a locus for albuminuria, and urinary protein loss is a risk factor for progressive CKD, we tested the hypothesis that common genetic variants in CUBN are associated with end-stage renal disease (ESRD) and proteinuria. First, a total of 1142 patients with ESRD, admitted for renal transplantation, and 1186 donors were genotyped for SNPs rs7918972 and rs1801239 (case-control study). The rs7918972 minor allele frequency (MAF) was higher in ESRD patients comparing to kidney donors, implicating an increased risk for ESRD (OR 1.39, p = 0.0004) in native kidneys. Second, after transplantation recipients were followed for 5.8 [3.8–9.2] years (longitudinal study) documenting ESRD in transplanted kidneys – graft failure (GF). During post-transplant follow-up 92 (9.6%) cases of death-censored GF occurred. Donor rs7918972 MAF, representing genotype of the transplanted kidney, was 16.3% in GF vs 10.7% in cases with functioning graft. Consistently, a multivariate Cox regression analysis showed that donor rs7918972 is a predictor of GF, although statistical significance was not reached (HR 1.53, p = 0.055). There was no association of recipient rs7918972 with GF. Rs1801239 was not associated with ESRD or GF. In line with an association with the outcome, donor rs7918972 was associated with elevated proteinuria levels cross-sectionally at 1 year after transplantation. Thus, we identified CUBN rs7918972 as a novel risk variant for renal function loss in two independent settings: ESRD in native kidneys and GF in transplanted kidneys.

Ancient founder mutation is responsible for Imerslund-Gräsbeck Syndrome among diverse ethnicities

BackgroundImerslund-Gräsbeck syndrome (IGS) was described just over 50 years ago by Olga Imerslund and Ralph Gräsbeck and colleagues. IGS is caused by specific malabsorption of cobalamin (Cbl) due to bi-allelic mutations in either the cubilin gene (CUBN) or the human amnionless homolog (AMN). Mutations in the two genes are commonly seen in founder populations or in societies with a high degree of consanguineous marriages. One particular mutation in AMN, c.208-2A>G, causing an out-of-frame loss of exon 4 in the mRNA, is responsible for some 15% of IGS cases globally. We present evidence that this founder mutation causes a substantial percentage of cases among diverse ethnicities and that the mutation is as old as human civilization.MethodsPartial genotyping indicated a founder event but its presence in diverse peoples of Arabic, Turkish, Jewish, and Hispanic ancestry suggested that the mutation might be recurrent. We therefore studied the flanking sequence spanning 3.5 Mb to elucidate the origin of the haplotype and estimate the age of the mutation using a Bayesian inference method based on observed linkage disequilibrium.ResultsThe mutation's distribution, the size of the shared haplotype, and estimates of growth rate and carrier frequency indicated that the mutation was a single prehistoric event. Dating back to the ancient Middle East around 11,600 BC, the mutation predates the advent of writing, farming, and the monotheistic religions of the region.ConclusionsThis mutation causes over 50% of the IGS cases among Arabic, Turkish, and Sephardic Jewish families, making it a primary target for genetic screening among diverse IGS cases originating from the Middle East. Thus, rare founder mutations may cause a substantial number of cases, even among diverse ethnicities not usually thought to be related.

No Association between Polymorphisms in Cubilin, a Gene of the Homocysteine Metabolism and the Risk of Non-Syndromic Cleft Lip with or without Cleft Palate

Epidemiological studies have correlated lower maternal periconceptional levels of plasma folate and cobalamin with increased risk of delivering offspring presenting congenital malformations such as cleft lip with or without cleft palate (CL/P) or neural tube defects. A number of genetic studies aimed at correlating these biochemical levels or the occurrence of malformations with specific genetic defects or polymorphisms have been successfully performed. The cubilin gene (CUBN) codes for a carrier that plays a crucial role in cobalamin cell internalization. CUBN polymorphisms were previously found to be associated with spina bifida occurrence. In this work, a family-based association study was performed to test CUBN involvement in CL/P. A sample of 391 CL/P triads was investigated with three single nucleotide polymorphisms mapping on the cubilin gene. Association tests indicated no significant association between CL/P and marker alleles or marker haplotypes. No evidence of maternal effect and imprinting were obtained. These data suggest that CUBN is not involved in CL/P onset in the investigated Italian population.

The role of cubilin gene polymorphisms and their influence on 25(OH)D 3 and 1,25(OH) 2D 3 plasma levels in type 1 diabetes patients

Background Megalin and cubilin bind and internalize the 25(OH)D 3–DBP complex in the kidney. Once the complex is internalized, 25(OH)D 3 is released and activated to 1,25(OH) 2D 3 the ligand for the vitamin D receptor (VDR). Supporting the important role of cubilin in this process recent findings showed that cubilin deficiency results in decrease of 25(OH)D 3 and 1,25(OH) 2D 3 plasma levels. Methods Two hundred T1D patients and healthy controls ( n = 200) were genotyped for five polymorphisms (rs3740168, rs3740165, rs1801233, rs1801229 and rs2796835) within the cubilin gene. The polymorphisms were analyzed by RFLP or real time PCR. Statistic analyses were performed by using allele-wise and genotype-wise χ 2 testing by using BiAS software. A p-value < 0.05 was considered as significant. Results We found that the genotype “AA” of the rs3740165 was more frequent in T1D patients compared to healthy controls (26.7% vs. 5.1%, p = 4 × 10 −7). Nevertheless no association between the rs3740165 polymorphism and the 25(OH)D 3 or 1,25(OH) 2D 3 plasma levels was found. No association with the other studied polymorphisms was observed. Conclusion Thus our findings reveal a novel association of the cubilin rs3740165 polymorphism with type 1 diabetes. Nevertheless how exactly this polymorphism could increase the risk to develop type 1 diabetes is subject for further investigations.