Impact of a chromosome X STR Decaplex in deficiency paternity cases

Abstract

Deficiency paternity cases, characterized by the absence of the alleged father, are a challenge for forensic genetics. Here we present four cases with a female child and a deceased alleged father in which the analysis of a set of 21 or 22 autosomal STRs (AS STRs) produced results within a range of doubt when genotyping relatives of the alleged father. Aiming to increase the Paternity Index (PI) and obtain more reliable results, a set of 10 X-linked STR markers, developed by the Spanish and Portuguese Group of the International Society for Forensic Genetics (ISFG), was then added. Statistical analysis substantially shifted the results towards the alleged fatherhood in all four cases, with more dramatic changes when the supposed half-sister and respective mother were the relatives tested.

Forensic Genetics and Genotyping

“…Markers located on this chromosome have a particular inheritance pattern, be-cause women are dizygous and men are hemizygous (54). The X chromosome markers (X-STRs and X-SNPs) show higher efficiency parameters than autosomes in special kinship investigations (as well as incest cases), involving mainly female offspring (48,53,54). The STRs on X chromosome can only be used in kinship analysis involving daughters, because there is no allele inherited by descent in a father-son relationship (54).…”

“…The X chromosome markers (X-STRs and X-SNPs) show higher efficiency parameters than autosomes in special kinship investigations (as well as incest cases), involving mainly female offspring (48,53,54). The STRs on X chromosome can only be used in kinship analysis involving daughters, because there is no allele inherited by descent in a father-son relationship (54). Therefore, a growing number of scientists researching X markers uses them for studying the genetic structure of human populations, ancestry proportions in admixed populations and for forensic investigations (53).…”

DNA Methods to Identify Missing Persons

“…Although, in a case of incest, little can be expected from the analysis of X-STR as all fetal alleles correspond to maternal alleles. So-called 'deficient' paternity cases show the greatest advantage for X-STRs (Trindade-Filho et al 2013). In the absence of a biological sample from the alleged father, DNA from relatives becomes a necessary prerequisite for X-STR analysis.…”