Paternity tests in Mexico: Results obtained in 3005 cases
Introduction
DNA analysis probably has become the most powerful tool for solving forensic cases related to criminal activity and for biological kinship establishment. Most of the paternity tests involve comparison of genetic profiles between the alleged father and child (including or not the mother), followed by exclusion of paternity or confirmation that require the paternity index (PI) estimation.1 Subsequently, probability of paternity (W) is computed applying the Bayes Theorem. Although the generally accepted minimum standard PI for inclusion of paternity is ≥ 100,2 presently most laboratories require a PI ≥ 10000, which corresponds to W ≥ 99.99% assuming a priori probability of paternity of 0.5.3 Biological kinship relationships can also be established by inclusion of additional relatives (reconstruction cases) and analysis of genetic markers with peculiar inheritance patterns. For instance, paternal kinship can be established between males carrying the same non-recombinant region of the Y-chromosome, and complex cases where at least one female is involved can be solved by means of X-linked STRs (X-STRs).4
Although PCR-based STR typing has been the method of choice for paternity testing,5,6 STRs sporadically are affected by gametic mutations that influence the test interpretation. Therefore, different authors and organizations have estimated mutation rates (μ) for loci commonly used for Human Identification (HID) purposes.7 Problems related to parentage testing gave rise to different national and international organizations, such as the International Society of Forensic Genetics (ISFG), Scientific Working Group on DNA Analysis Methods (SWGDAM), and the American Association of Blood Banks (AABB), among others. These groups have published recommendations and coordinated exercises to compare DNA typing results between participating laboratories.1,3,6,8, 9, 10, 11, 12 However, these reports commonly omit information of some populations, mainly from developing countries. For instance, only two old reports exist regarding the non-paternity frequency in Mexico.13,14 Consequently, the aim of this study is to analyze paternity testing data of a Mexican laboratory during a period of five years, such as type of paternity cases, non-paternity prevalence, number of exclusions and a posteriori information given by some of the HID kits employed in the lab, null alleles, triallelic patterns, and mutation rates.
Section snippets
Information dataset
Information dataset was obtained from paternity cases performed over a period of five years by a Mexican laboratory of genetics (www.dnaprofile.com.mx). During the database creation, personal information of individuals involved in paternity cases was not shared according to legal regulations (Ley federal de protección de datos personales, México). The laboratory participates in two quality control proficiency tests annually organized by the Spanish and Portuguese-Speaking Working Group of the
Type of DNA parentage tests
We collected 3005 cases from different states of Mexico during a period of five years (2010–2015) (Supplementary Table S1). Motherless were the most common tests (77.27%), followed by trios including the mother (20.7%) (Table 1). The remaining 2.04% included different reconstruction cases where the alleged parent is missing and additional relatives were used to evaluate the biological kinship. Most of these cases were solved with lineage markers according to the analyzed biological
Conclusions
This is the first study in Mexico that describes different a posteriori parameters from DNA paternity tests. Interestingly, motherless tests were the most frequently solved (77.3%). The paternity testing exclusion rate was around 30%. The HID kits including ≥20 STRs in motherless tests showed higher PI values to conclude paternity, and lower number of inconclusive cases by isolated exclusions (<3 loci) than one HID kit based on 15 STRs. In general, STR mutation rates estimated herein are in
Funding sources
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Conflicts of interest
The authors declare no conflicts of interest.
References (47)
- et al.
ISFG: recommendations on biostatistics in paternity testing
For Sci Int
(2007) - et al.
A report of the 2009-2011 paternity and relationship testing workshops of the English speaking working groupof the international society for forensic genetics
Forensic Sci Int
(2014) Forensic typing of short tandem repeat markers on the X and Y chromosomes
Forensic Sci Int
(2015)- et al.
The problem of single parent/child paternity analysis Practical results involving 336 children and 348 unrelated men
For Sci Int
(2006) - et al.
A report of the 2002–2008 paternity testing workshops of the English speaking working group of the international society for forensic genetics
For Sci Int
(2009) - et al.
Paternity testing commission of the international society of forensic genetics: recommendations on genetic investigations in paternity cases paternity testing commission of the international society of forensic genetics
Forensic Sci Int
(2002) Validation of software for calculating the likelihood ratio for parentage and kinship
For Sci Int
(2009)- et al.
Genetic data of 15 autosomal STRs (identifiler kit) of three Mexican Mestizo population samples from the states of Jalisco (west), Puebla (center), and Yucatan (southeast)
Forensic Sci Int
(2009) - et al.
Beyond traditional paternity and identification cases. Selecting the most probable pedigree
Forensic Sci Int
(2000) - et al.
DNA paternity tests in Spain without the mother's consent: the legal responsibility of the laboratories
Forensic Sci Int
(2014)