DNA analysis in a paternity case involving a triploid fetus

Area of Science:

• Forensic Genetics
• Reproductive Biology
• Cytogenetics

Background:

• Paternity testing was requested in a sexual assault case involving a conception.
• Samples included maternal blood, alleged father's blood, and fetal blood.
• The case presented unique challenges due to the fetus's genetic makeup.

Purpose of the Study:

• To determine paternity in a case involving a sexual assault.
• To address the complexities of DNA analysis for a triploid fetus.
• To establish a statistically sound method for paternity index calculation in triploidy.

Main Methods:

• DNA typing utilizing restriction fragment length polymorphism (RFLP) and polymerase chain reaction/short-tandem repeat (PCR/STR) analysis at 13 genetic loci.
• Fluorescent in situ hybridization (FISH) with chromosome-specific probes confirmed triploidy in fetal trophoblast nuclei.
• A modified likelihood ratio (LR) calculation was developed, using the reciprocal of the random men not excluded (RMNE) value.

Main Results:

• Initial DNA profiles suggested the fetus was triploid.
• FISH analysis confirmed the presence of three sets of chromosomes (triploidy).
• Standard paternity index calculations were not feasible due to the inability to distinguish dispermy from diandry.

Conclusions:

• The modified likelihood ratio, based on the exclusionary power of DNA markers, is suitable for assessing paternity in triploid cases.
• This method accounts for the two transmitted paternal genes characteristic of triploidy.
• Accurate statistical interpretation is crucial for assigning weight to DNA matches in complex parentage testing scenarios.