Maternal SNPs in the p53 Pathway: Risk Factors for Trisomy 21?

41 Disease Markers 34 (2013) 41–49 DOI 10.3233/DMA-2012-00937 IOS Press Maternal SNPs in the p53 pathway: Risk factors for trisomy 21? Juliano André Boquetta,b,d , Ana Paula Carneiro Brandalizea,b,c, Lucas Rosa Fragaa,b,d and Lavı́nia Schuler-Faccinia,b,c,d,∗ Departamento de Genética, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil Programa de Pós-Graduação em Genética e Biologia Molecular, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil c Serviço de Genética Médica, Hospital de Clı́nicas de Porto Alegre, Porto Alegre, Brazil d Instituto Nacional de Genética Médica Populacional – INAGEMP, Porto Alegre, Brazil a b Abstract. The p53 family and its regulatory pathway play an important role as regulators of developmental processes, limiting the propagation of aneuploid cells. Its dysfunction or imbalance can lead to pathological abnormalities in humans. The aim of this study was to evaluate the effect of maternal polymorphisms TP53 c.215G>C (P72R), TP73 4 c.-30G>A and 14 c.-20C>T, MDM2 c.14+309T>G (SNP309), MDM4 c.753+572C>T and USP7 c.2719-234G>A as risk factors for Down Syndrome (DS) birth. A case-control study was conducted with 263 mothers of DS children and 196 control mothers. The distribution of these genotypic variants was similar between case and control mothers. However, the combined alleles TP53 C and MDM2 G, and TP53 C and USP7 A increased the risk of having offspring with DS (OR = 1.84 and 1.77; 95% CI; P < 0.007 and 0.018, respectively). These results suggest that, although the individual polymorphisms were not associated with DS birth, the effect of the combined genotypes among TP53, MDM2 and USP7 genes indicates a possible role of TP53 and its regulatory pathway as a risk factor for aneuploidy. Keywords: Down syndrome, TP53, TP73, MDM2, MDM4, USP7 1. Introduction Down Syndrome (DS), characterized by trisomy of chromosome 21, is the most common cause of mental retardation in humans [23], occurring in 1 in 700– 800 births [30]. The meiotic nondisjunction is the main cause of free 21 trisomy, event responsible for the aneuploidy 21 in 95% of affected individuals [3]. In 95% of cases, the nondisjunction occurs during maternal meiosis [1], mainly in the first meiotic division [2,59]. It is well established that advanced maternal age is a risk factor for aneuploidy and is associated specifically with errors that occur during oogenesis [59]. Given the important role played by p53 family proteins as regulators of crucial developmental processes, ∗ Corresponding author: Lavı́nia Schuler-Faccini, Departamento de Genética, Universidade Federal do Rio Grande do Sul, Caixa Postal 15053, Agencia Campus UFRGS, CEP 91501-970/Porto Alegre RS, Brazil. Tel.: +51 33086726; Fax: +51 33598010; E-mail: . their dysfunction or imbalance can lead to pathological abnormalities in humans. Genomic instability, aneuploidy and copy number polymorphisms that originate in the female germline and contribute to a number of developmental defects can be explored through investigations of the TP53 gene family [26]. Encoded by TP53 gene, the p53 protein has known importance in the prevention of tumors and genomic stability in somatic cells, acting as a transcription factor that regulates a large number of genes in response to cell damage, including activation of oncogenes and DNA damage [12,35,45]. When activated, p53 initiates cellular responses, such as cell cycle arrest, DNA repair, senescence and apoptosis [22,27]. The loss of p53 allows the accumulation of aneuploid cells as a result of chromosomal instability. Thus, p53 and its regulatory pathway play a critical role in limiting the propagation of aneuploidy and preserving the nature of diploid human cells [55]. The central control of the p53 regulatory pathway consists of three major genes and their products: ISSN 0278-0240/13/$27.50  2013 – IOS Press and the authors. All rights reserved 42 J.A. Boquett et al. / Maternal SNPs in the p53 pathway: Risk factors for trisomy 21? MDM2 (Mouse double minute p53 binding protein homolog 2), MDM4 (Mouse double minute p53 binding protein homolog 4) and USP7 (ubiquitin specific peptidase 7 (herpes virus-associated)), also known as HAUSP [10,29]. The main negative regulator of the TP53 is the protein MDM2, which acts on the p53 as an E3 ubiquitin ligase, leading to degradation of p53 [9, 31]. MDM2 is upregulated by TP53, where the increase in p53 levels leads to increased transcription of MDM2. Thus, the product degrades p53 by inhibiting their levels, resulting in a negative feedback loop. This process maintains the p53 protein at low level in the absence of stress signals, allowing normal cell proliferation [42, 47]. Participating in the same metabolic pathway, the TP73 gene plays a crucial role in maintaining the rate of ovulation and acting on the spindle checkpoint, reducing aneuploidy in the offspring [57]. p73 plays an important role in maintaining genomic integrity as well, which is particularly important when p53 function is compromised [5]. Single nucleotide polymorphisms (SNPs) in genes of the p53 regulatory pathway have been targeted for study in research relating to human reproduction [16, 17,29]. A common polymorphism in TP53 c.215G>C (P72R, rs1042522) [11], a substitution at codon 72 that makes the induction of apoptosis less efficient [15,54]. The MDM2 gene has an important functional polymorphism c.14+309T>G (SNP309, rs2279744), the result of a thymine to guanine change in its promoter region [7], increasing MDM2 expression and attenuating the p53 function [7,16,29]. A substitution in intron 9 of MDM4 gene c.753+572C>T (rs1563828) is correlated with human reproduction, as well as c.2719-234G>A change in intron 25 of USP7 gene (rs1529916) [29]. In TP73, two closely linked polymorphisms in position 4 c.-30G>A and 14 c.-20C>T (rs2273953, rs1801173) are located before the initiating codon in exon 2. This region can form a clamp-shaped structure with the potential to interfere in gene expression [28]. Thus, we hypothesized that polymorphisms related to TP53 and TP73 genes and genes in their regulatory pathway – MDM2, MDM4 and USP7 – may be closely associated with human reproduction, where its fine regulation is extremely important in maintaining genomic stability of germline cells avoiding aberrations in its genome, as aneuploidies. This study investigated the influence of the TP53 gene family and their regulators as risk factors for aneuploidy of chromosome 21. We analyzed the role of TP53 c.215G>C polymorphism (rs1042522), TP73 c.-30G>A (rs2273953) and c.-20C>T (rs1801173), MDM2 c.14+309T>G (rs2279744), MDM4 c.753+572C>T (rs1563828) and USP7 c.2719-234G>A (rs1529916) as maternal risk factors for DS birth in a case-control study. 2. Materials and methods 2.1. Subjects All cases were identified through Medical Genetic Service of Hospital de Clı́nicas de Porto Alegre (HCPA) and local support groups of DS (APAEs). The control group con (...truncated)