The aim of this study was to assess the association between IRF6 single nucleotide polymorphisms and nonsyndromic cleft lip, with or without cleft palate (NSCL/P), in a Chilean population, based on a case-control sample and confirmed in a case-parent trio population. In a sample of 150 Chilean case-parent trios and 164 controls (cohort 1), we evaluated the association between three common IRF6 variants (rs764093, rs2236909, rs2235375) and NSCL/P using odds ratio (OR) for case-control and case-parent trios and in a combined OR of both designs. To confirm associations from the cohort 1, we increased the sample size to 215 triads and 320 controls (cohort 1 + cohort 2). The combined OR for the cohort 1 reveals that the rs2235375 C allele is associated with NSCL/P in Chile (OR 1.34; p = 0.013), which was supported by the results for the two cohorts (OR 1.29; p = 0.006). Bioinformatic prediction showed that this variant, located 27 bp downstream from IRF6 exon 6, potentially alters the splicing process and based on functional annotations is associated with a decrease of gene expression. We propose that the C allele of rs2235375 from IRF6 gene seems to be a risk factor for NSCL/P in a Chilean population. However, we cannot discard a population stratification bias in our findings. On the other hand, further studies are necessary to confirm the biological role of rs2235375 in IRF6 function at craniofacial development level.

Non-syndromic cleft lip with or without cleft palate (NSCL/P) is the most common craniofacial birth defect in humans, the etiology of which can be dependent on the interactions of multiple genes. We previously reported haplotype associations for polymorphic variants of interferon regulatory factor 6 (IRF6), msh homeobox 1 (MSX1), bone morphogenetic protein 4 (BMP4), and transforming growth factor beta 3 (TGFB3) in Chile. Here, we analyzed the haplotype-based gene-gene interaction for markers of these genes and NSCL/P risk in the Chilean population. We genotyped 15 single nucleoptide polymorphisms (SNPs) in 152 Chilean patients and 164 controls. Linkage disequilibrium (LD) blocks were determined using the Haploview software, and phase reconstruction was performed by the Phase program. Haplotype-based interactions were evaluated using the multifactor dimensionality reduction (MDR) method. We detected two LD blocks composed of two SNPs from BMP4 (Block 1) and three SNPs from IRF6 (Block 2). Although MDR showed no statistical significance for the global interaction model involving these blocks, we found four combinations conferring a statistically significantly increased NSCL/P risk (Block 1-Block 2): T-T/T-G C-G-T/G-A-T; T-T/T-G C-G-C/C-G-C; T-T/T-G G-A-T/G-A-T; and T-T/C-G G-A-T/G-A-T. These findings may reflect the presence of a genomic region containing potential causal variants interacting in the etiology of NSCL/P and may contribute to disentangling the complex etiology of this birth defect.

En este artículo se presenta un análisis epidemiológico genético de un grupo de familias afectadas de labio hendido con o sin paladar hendido (LH±PH) seleccionadas de la población de Antioquia (Colombia). La finalidad es discriminar el componente genético y el componente ambiental involucrados en la susceptibilidad para desarrollar LH±PH. En primera instancia se calculó una heredabilidad del 96% lo cual está en contra del modelo multifactorial y es más compatible con el modelo que postula la existencia de un gen con efecto mayor. Los resultados del análisis de segregación simple se ajustaron mejor al modelo de locus mayor recesivo con penetrancia incompleta. La frecuencia del gen mayor que induce la susceptibilidad para desarrollar LH±PH es de 0.037 dentro de la población que fue estudiada. Mediante una prueba de asociación de marcadores genéticos se encontró una covarianza significante entre el fenotipo LH±PH y el genotipo JKa/JKa (grupo sanguíneo Kidd, p<0.01, riesgo relativo igual a 0.2). El resultado anterior es compatible con la existencia de un efecto protector para el desarrollo de LH±PH. A partir de dicha asociación, se hizo un análisis secuencial de ligamiento entre LH±PH y el marcador sanguíneo Kidd mediante la genotipificación de una familia extendida de gran tamaño, lo que dio un LOD SCORE de -1. Este resultado de LOD-SCORE no permite confirmar ni descartar ligamiento. Los anteriores hallazgos sugieren que los efectos ambientales, considerados como el factor más importante en la génesis LH±PH son mínimos en la generación de susceptibilidad para desarrollar LH±PH, y por lo tanto es necesario considerar el modelo de gen mayor.

OBJECTIVE:The functional variant within the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene c.677C>T, producing alterations in folate metabolism, has been associated with the risk of non-syndromic cleft lip with or without cleft palate (NSCL/P). We assessed this association in a Chilean population using a combined analysis of case-control and case-parent trio samples.SUBJECTS AND METHODS:Samples of 165 cases and 291 controls and 121 case-parent trios (sharing the cases) were genotyped. Odds ratio (OR) was estimated for case-control (allele and genotype frequency differences), and this result was confirmed by allele transmission distortion in trios. Due to that these samples are not independent, a combined OR was also computed. Maternal genotype effect was additionally evaluated based on a log-linear method.RESULTS:Borderline but not significant OR (1.28; CI 0.97-1.69) was observed for risk allele (T) in the case-control sample. However, triad sample showed a significant association (OR 1.56: CI 1.09-2.25) which was confirmed by the combined OR (1.37; CI 1.11-1.71). Maternal genotype has been also associated with the phenotype (P = 0.002).CONCLUSIONS:In contrast to previous reports considering Chilean subjects, our results demonstrated that the offspring and maternal genotypes for MTHFR c.677C>T variant are strongly associated with NSCL/P in this Chilean population.

Animal models have shown evidence of the role of maternal methyl donor status and its metabolism (one-carbon metabolism) in normal embryonic maxillofacial development. Nevertheless, studies in humans have shown conflicting results for the association of maternal methylation status biomarkers in the aetiology of the main craniofacial birth defects: non-syndromic orofacial clefts (NSOFCs). The aim of this study was to perform a meta-analysis assessing the relationship between maternal levels of methylation status biomarkers (plasma and erythrocyte folates and plasma vitamin B12 and homocysteine) and the risk of NSOFCs. A literature search of the conventional and grey medical-scientific databases identified 12 studies considering these variables. Based on standardized differences between means among cases and controls (Cohen's d test), evidence was found of an association only with high plasma homocysteine (d=0.37; P=0.026) when single effects were pooled. In addition to its usefulness as a marker of poor methyl-donor intake and/or metabolism, homocysteine appears to have a teratogenic effect. Although the results are based on a relatively small number of reports and/or studies of small sample sizes showing between-study heterogeneity, these problems were resolved by including an additional analysis. Therefore these findings constitute a real contribution towards explaining the complex aetiology of orofacial clefts.

Instituto de Investigaci on en Ciencias Odontol ogicas, Facultad de Odontolog ıa, Universidad de Chile, Santiago; Programa de Gen etica Humana, Instituto de Ciencias Biom edicas, Facultad de Medicina, Universidad de Chile, Santiago; Programa de Anatom ıa y Biolog ıa del Desarrollo, Instituto de Ciencias Biom edicas, Facultad de Medicina, Universidad de Chile, Santiago; Servicio de Anatom ıa Patol ogica, Hospital Cl ınico de la Universidad de Chile, Santiago; Secci on de Gen etica, Hospital Cl ınico Universidad de Chile, Santiago; Unidad de Neonatolog ıa, Hospital Cl ınico Universidad de Chile, Santiago; Unidad de Gen etica, Hospital Dr. S otero del R ıo, Santiago, Chile

Orofacial clefts are the most prevalent birth defects that affect craniofacial structures and implicate genetic and environmental factors in their aetiology. Maternal metabolic state and nutrition have been related to these and other structural malformations, and studies of maternal obesity before pregnancy have shown controversial results about its association with the risk of orofacial clefts in their offspring. Our aim was to assess the combined effect of several single studies of maternal obesity on the risk of orofacial clefts using meta-analysis. We searched for these reports in the PubMed database, and selected 8 studies that met our criteria for eligibility. As a result of this analysis, and using maternal normal weight as a reference, we found that maternal obesity does increase the risk of orofacial clefts in their offspring (OR 1.18, 95% CI 1.11 to 1.26). When these clefts are considered separately, maternal obesity is associated with cleft lip with or without cleft palate (OR 1.13, 95% CI 1.04 to 1.23), and with cleft palate alone (OR 1.22, 95% CI 1.09 to 1.35). Our results support the relation between maternal obesity and orofacial clefts, and confirm two previous meta-analyses that considered fewer studies. However, the molecular mechanisms underlying this statistical evidence have not been fully elucidated.

BACKGROUND:Germline mutations in PALB2 have been identified in approximately 1% of familial breast cancer (BC) in several populations. Nevertheless its contribution in the South-American population is unknown. The goal of this study was to determine the prevalence of PALB2 mutations in the Chilean population. METHODS:100 Chilean BRCA1/2-negatives familial BC cases were included for the PALB2 mutation analysis. We use conformational sensitive gel electrophoresis and direct sequencing. Using a case-control design, we studied the identified variants in 436 BC cases and 809 controls to evaluate their possible association with BC risk. RESULTS:No pathogenic mutations were detected. We identified three variants, the variant c.1861C > A not previously described was found in one of the 436 cases and none of the 809 controls. The bioinformatic analyses indicate that this variant probably is not pathogenic. PALB2 c.1676A > G (rs152451A/G) and c.2993C > T (rs45551636C/T) variants were significantly associated with increased BC risk only in cases with a strong family history of BC (OR = 1.9 [CI 95% 1.3-2.8] p < 0.01 and OR = 3.3 [CI 95% 1.4-7.3] p < 0.01, respectively). The rs152451A/G-rs45551636C/T composite genotype produce increase of the BC risk in cases with a strong family history of BC (OR = 3.6 [CI 95% 1.7-8.0] p = 0.003). The rs152451-G/rs45551636-C and rs152451-G/rs45551636-T haplotypes were associated with an increased BC risk only in cases with a strong family history of BC (OR = 1.6 [CI 95% 1.0-2.5] p = 0.05 and OR = 3.7 [CI 95% 1.8-7.5] p < 0.001, respectively). CONCLUSION:Our results suggest that PALB2 c.1676A > G and c.2993C > T play roles in BC risk in women with a strong family history of BC.

Background: Mandatory fortification with folic acid (FA) was implemented in Chile in 2000. Thereafter, the rate of spina bifida decreased by 52 to 55%. Genetic abnormalities in folate metabolism may be involved in the etiology of spina bifida. Aim: To evaluate the association between myelomeningocele (MM) and c.A1298C and c.C677T polymorphisms within the coding gene for 5,10-methylenetetrahydrofolate reductase (MTHFR) in the Chilean population. Material and Methods: These polymorphisms were genotyped in 105 patients showing isolated MM, born after the onset of FA fortification, and in their parents. The transmission disequilibrium test (TDT) was performed to evaluate alterations in the transmission of both alleles and haplotypes MTHFR polymorphism. We also evaluated the presence of parent-origin-effect (POE) of alleles using the Clayton's extension of the TDT. Results: TDT analysis showed no significant distortions in the transmission of alleles or haplotypes. Moreover, although the POE showed increased risk for maternally derived allele, this risk was not statistically significant. Conclusions: The studied variants in the MTHFR gene (c.C677T and c.A1298C) do not constitute risk factors for MM in this sample of Chilean patients and their parents.

Recent Genome-Wide Association Studies have identified several single nucleotide polymorphisms (SNPs) associated with breast cancer (BC) among women of Asian, European, and African-American ancestry. Nevertheless, the contribution of these variants in the South American population is unknown. Furthermore, there is little information about the effect of these risk alleles in women with early BC diagnosis. In the present study, we evaluated the association between rs3803662 (TOX3, also known as TNRC9), rs13387042 (2q35), and rs13281615 (8q24) with BC risk in 344 Chilean BRCA1/2-negative BC cases and in 801 controls. Two SNPs, rs3803662 and rs13387042, were significantly associated with increased BC risk in familial BC and in non-familial early-onset BC. The risk of BC increased in a dose-dependent manner with the number of risk alleles (P-trend < 0.0001 and 0.0091, respectively). The odds ratios for BC in familial BC and in early-onset non-familial BC were 3.76 (95 %CI 1.02-13.84, P = 0.046) and 8.0 (95 %CI 2.20-29.04, P = 0.002), respectively, for the maximum versus minimum number of risk alleles. These results indicate an additive effect of the TOX3 rs3803662 and 2q35 rs13387042 alleles for BC risk. We also evaluated the interaction between rs3803662 and rs13387042 SNPs. We observed an additive interaction only in non-familial early-onset BC cases (AP = 0.72 (0.28-1.16), P = 0.001). No significant association was observed for rs13281615 (8q24) with BC risk in women from the Chilean population. The strongly increased risk associated with the combination of low-penetrance risk alleles supports the polygenic inheritance model of BC.

Methylenetetrahydrofolate reductase polymorphisms as risk factors for myelomeningoceleBackground: Mandatory fortification with folic acid (FA) was implemented in Chile in 2000.Thereafter, the rate of spina bifida decreased by 52 to 55%.Genetic abnormalities in folate metabolism may be involved in the etiology of spina bifida.Aim: To evaluate the association between myelomeningocele (MM) and c.A1298C and c.C677T polymorphisms within the coding gene for 5,10-methylenetetrahydrofolate reductase (MTHFR) in the Chilean population.Material and Methods: These polymorphisms were genotyped in 105 patients showing isolated MM, born after the onset of FA fortification, and in their parents.The transmission disequilibrium test (TDT) was performed to evaluate alterations in the transmission of both alleles and haplotypes MTHFR polymorphism.We also evaluated the presence of parent-origin-effect (POE) of alleles using the Clayton's extension of the TDT.Results: TDT analysis showed no significant distortions in the transmission of alleles or haplotypes.Moreover, although the POE showed increased risk for maternally derived allele, this risk was not statistically significant.Conclusions: The studied variants in the MTHFR gene (c.C677T and c.A1298C) do not constitute risk factors for MM in this sample of Chilean patients and their parents.(

It has been widely accepted that nonsyndromic cleft lip with or without cleft palate (NSCLP) depends on the altered function of several genes during craniofacial development. The construction of genetic risk score (GRS) have allowed to estimate the combined effect of risk alleles from genes interacting in different molecular pathways in order to improve an estimation of the individual's susceptibility to a complex disease. The aim of our study was to construct a GRS considering markers showing previous allele/haplotype association with NSCLP in Chile. Considering 10 risk markers from IRF6, MSX1, BMP4 and TGFB3 genes, we estimate a GRS for each of 152 NSCLP cases and 164 controls. GRS showed no significant results when comparing cases and controls for these markers. These results could be explained by a possible indirect relationship of these genes between them in NSCLP which GRS is not capable of detecting and/or the modest number of risk alleles considered herein.

Genome-Wide Association Studies have identified several loci associated with breast cancer (BC) in populations of different ethnic origins. One of the strongest associations was found in the FGFR2 gene, and MAP3K1 has been proposed as a low-penetrance BC risk factor. In this study, we evaluated the associations among FGFR2 SNPs rs2981582, rs2420946, and rs1219648; and MAP3K1 rs889312, with BC risk in 351 BRCA1/2-negative Chilean BC cases and 802 controls. All the SNPs studied were significantly associated with increased BC risk in familial BC and in non-familial early-onset BC, in a dose-dependent manner. Subjects with 3 risk alleles were at a significantly increased risk of BC compared with subjects with 0-2 risk alleles, in both familial BC and early-onset non-familial BC (OR = 1.47, 95 % CI 1.04-2.07, P = 0.026 and OR = 2.04 95 % CI 1.32-3.24, P < 0.001, respectively). In the haplotype analysis, the FGFR2 rs2981582 T / rs2420946 T / rs1219648 G haplotype (ht2) was associated with a significantly increased BC risk compared with the rs2981582 C / rs2420946 C / rs1219648 A haplotype in familial BC and in non-familial early-onset BC (OR = 1.32, 95 % CI 1.06-1.65, P = 0.012; OR = 1.46, 95 % CI 1.11-1.91, P = 0.004, respectively). When the FGFR2 ht2 and MAP3K1 rs889312 were evaluated as risk alleles, the risk of BC increased in a dose-dependent manner as the number of risk alleles increased (P trend <0.0001), indicating an additive effect. Nevertheless, there is no evidence of an interaction between FGFR2 ht2 and the MAP3K1 rs889312 C allele. These findings suggest that genetic variants in the FGFR2 and MAP3K1 genes may contribute to genetic susceptibility to BC.

Since the discovery of the BRCA1 and BRCA2 genes, much work has been carried out to identify further breast cancer (BC) susceptibility genes. BARD1 (BRCA1-associated ring domain) was originally identified as a BRCA1-interacting protein but has also been described in tumor-suppressive functions independent of BRCA1. Some association studies have suggested that the BARD1 Cys557Ser variant might be associated with increased risk of BC, but others have failed to confirm this finding. To date, this variant has not been analyzed in Spanish or South-American populations. In this study, using a case-control design, we analyzed the C-terminal Cys557Ser change in 322 Chilean BC cases with no mutations in BRCA1 or BRCA2 and in 570 controls in order to evaluate its possible association with BC susceptibility. BARD1 Cys557Ser was associated with an increased BC risk (P = 0.04, OR = 3.4 [95 % CI 1.2-10.2]) among cases belonging to families with a strong family history of BC. No difference between single cases affected with age <50 years at diagnosis (n = 117) and controls was observed for carriers of Cys/Ser genotype. It is likely that this variant is not involved in BC risk in this group of women. We also analyzed a possible interaction between BARD1 557Ser/XRCC3 241Met variants considering the role of both genes in the maintenance of genome integrity. The combined genotype Cys/Ser-carrier with the XRCC3 241Met allele was associated with an increased BC risk (P = 0.02, OR = 5.01 [95 % CI 1.36-18.5]) among women belonging to families with at least three BC and/or ovarian cancer cases. Our results suggest that BARD1 557Ser and XRCC3 241Met may play roles in BC risk in women with a strong family history of BC. Nevertheless there is no evidence of an interaction between the two SNPs. These findings should be confirmed by other studies and in other populations.

INTRODUCCIÓN: la fisura labio palatina no sindrómica, NSCLP (del inglés Nonsyndromic cleft lip and palate) es una de las malformaciones congénitas más frecuentes tanto en Chile como en el resto del mundo. Presenta un modo de herencia multifactorial, en la que interactúan varios genes y el medio ambiente. Evidencias experimentales han demostrado la participación de Sonic hedgedhog (Shh) en la migración de las células de la cresta neural, en la transformación epitelio-mesénquima y en la formación de las estructuras medias craneofaciales durante el desarrollo embrionario, es probable una asociación entre variantes de Shh y la NSCLP. MÉTODOS: el objetivo de este trabajo fue evaluar las regiones exónicas e intrónicas adyacentes de Shh, en una muestra de 150 tríos caso-progenitores para hallar la asociación con NSCLP. Se utilizó el método PCR-RFLP para determinar la presencia de heterodúplex. Luego, se utilizó la técnica de Conformation Sensitive Gel Electrophoresis (CSGE) para ver la distorsión del ADN en los heterodúplex. Como método alternativo, se hizo un análisis de polimorfismos de un solo nucleótido (del inglés single-nucleotide polymorphism SNP) para determinar asociación entre NSCLP y Shh, para lo cual se utilizaron los SNP: rs1233555 y rs1233556, ubicados en el primer intrón de Shh. RESULTADOS: el objetivo de este trabajo fue evaluar las regiones exónicas e intrónicas adyacentes de Shh, en una muestra de 150 tríos caso-progenitores para hallar la asociación con NSCLP. Se utilizó el método PCR-RFLP para determinar la presencia de heterodúplex. Luego, se utilizó la técnica de Conformation Sensitive Gel Electrophoresis (CSGE) para ver la distorsión del ADN en los heterodúplex. Como método alternativo, se hizo un análisis de polimorfismos de un solo nucleótido (del inglés single-nucleotide polymorphism SNP) para determinar asociación entre NSCLP y Shh, para lo cual se utilizaron los SNP: rs1233555 y rs1233556, ubicados en el primer intrón de Shh. CONCLUSIÓN: la no asociación puede deberse a que la frecuencia de distribución de los SNP en la población chilena es diferente a la de las poblaciones referidas, o a que el número de SNP analizados fue insuficiente, o la no inclusión para el análisis de otras regiones de Shh.

BACKGROUND:Bone morphogenetic protein 4 gene (BMP4) plays a key role during maxillofacial development, since orofacial clefts are observed in animals when this gene is conditionally inactivated. We recently reported the existence of association between nonsyndromic cleft lip/palate (NSCLP) and BMP4 polymorphisms by detecting transmission deviations for haplotypes that include a region containing a BMP4 promoter in case-parent trios. The aim of the present study was to search for possible causal mutations within BMP4 promoters (BMP4.1 and BMP4.2).METHODS:We analyzed the sequence of BMP4.1 and BMP4.2 in 167 Chilean NSCLP cases and 336 controls.RESULTS:We detected three novel variants in BMP4.1 (c.-5514G > A, c.-5365C > T and c.-5049C > T) which could be considered as cleft risk factors due to their absence in controls. Additionally, rs2855530 G allele (BMP4.2) carriers showed an increased risk for NSCLP restricted to males (OR = 1.52; 95% C.I. = 1.07-2.15; p = 0.019). For this same SNP the dominant genotype model showed a higher frequency of G/G+G/C and a lower frequency of C/C in cases than controls in the total sample (p = 0.03) and in the male sample (p = 0.003). Bioinformatic prediction analysis showed that all the risk variants detected in this study could create new transcription factor binding motifs.CONCLUSIONS:The sex-dependent association between rs2855530 and NSCLP could indirectly be related to the differential gene expression observed between sexes in animal models. We concluded that risk variants detected herein could potentially alter BMP4 promoter activity in NSCLP. Further functional and developmental studies are necessary to support this hypothesis.

The distribution of BRCA1/2 germline mutations in breast/ovarian cancer (BC/OC) families varies among different populations. In the Chilean population, there are only two reports of mutation analysis of BRCA1/2, and these included a low number of BC and/or OC patients. Moreover, the prevalence of BRCA1/2 genomic rearrangements in Chilean and in other South American populations is unknown. In this article, we present the mutation-detection data corresponding to a set of 326 high-risk families analyzed by conformation-sensitive gel electrophoresis and heteroduplex analysis. To determine the contribution of BRCA1/2 LGRs in Chilean BC patients, we analyzed 56 high-risk subjects with no pathogenic BRCA1/2 point mutations. Germline BRCA1/2 point mutations were found in 23 (7.1%) of the 326 Chilean families. Families which had at least three BC and/or OC cases showed the highest frequency of mutations (15.9%). We identified 14 point pathogenic mutations. Three recurrent mutations in BRCA1 (c.187_188delAG, c.2605_2606delTT, and c.3450_3453delCAAG) and three in BRCA2 (c.4969_4970insTG, c.5374_5377delTATG, and c.6503_6504delTT) contributed to 63.6 and 66.7% of all the deleterious mutations of each gene, which may reflect the presence of region-specific founder effects. Taken together BRCA1/2 recurrent point mutations account for 65.2% (15/23) of the BRCA1/2 (+) families. No large deletions or duplications involving BRCA1/2 were identified in a subgroup of 56 index cases negative for BRCA1/2 point mutations. Our study, which is the largest conducted to date in a South American population, provides a comprehensive analysis on the type and distribution of BRCA1/2 mutations and allelic variants.

Objective To assess the possible association between TGFB3 allele variants and nonsyndromic cleft lip with or without cleft palate in a Chilean population. Design In our study we used a case-parents trios design. The sample consisted of 150 unrelated trios ascertained through probands affected with nonsyndromic cleft lip with or without cleft palate. Three TGFB3 polymorphisms were analyzed (rs2268626, rs2268625, and rs3917201). An allele/haplotype transmission disequilibrium test was used to evaluate the possible genotype-phenotype association. Results An overtransmission from parents to affected progeny was observed for the A allele of rs3917201 (p = .03) and for the rs2268625-rs3917201 A-A haplotype (p = .022). A defect of transmission of rs2268625-rs3917201 G-G haplotype (p = .022) was observed also. Conclusions Allelic and haplotypic associations implicate a possible role of TGFB3 in nonsyndromic cleft lip with or without cleft palate in the Chilean population. Additional studies are needed in order to elucidate the possible mechanisms that can explain the role of TGFB3 genetic variants in the condition.

The double-strand break (DSB) DNA repair pathway has been implicated in breast cancer (BC). RAD51 and its paralogs XRCC3 and RAD51D play an important role in the repair of DSB through homologous recombination (HR). Some polymorphisms including XRCC3-Thr241Met, RAD51-135G > C, and RAD51D-E233G have been found to confer increased BC susceptibility. In order to detect novel mutations that may contribute to BC susceptibility, 150 patients belonging to 150 Chilean BRCA1/2-negative families were screened for mutations in XRCC3. No mutations were detected in the XRCC3 gene. In addition, using a case-control design we studied the XRCC3-Thr241Met, and RAD51D-E233G polymorphisms in 267 BC cases and 500 controls to evaluate their possible association with BC susceptibility. The XRCC3 Met/Met genotype was associated with an increased BC risk (P = 0.003, OR = 2.44 [95%CI 1.34-4.43]). We did not find an association between E233G polymorphism and BC risk. We also analyzed the effect of combined genotypes among RAD51-135G > C, Thr241Met, and E233G polymorphisms on BC risk. No interaction was observed between Thr241Met and 135G > C. The combined genotype Thr/Met-E/G was associated with an increased BC risk among women who (a) have a family history of BC, (b) are BRCA1/2-negative, and (c) were < 50 years at onset (n = 195) (P = 0.037, OR = 10.5 [95%CI 1.16-94.5]). Our results suggested that the variability of the DNA HR repair genes XRCC3 and RAD51D may play a role in BC risk, but this role may be underlined by a mutual interaction between these genes. These findings should be confirmed in other populations.