Genetic analysis of chromosome 2 copy-neutral loss of heterozygosity in paternity testing

This study investigates the cause of a non-Mendelian inheritance pattern observed at short tandem repeat (STR) loci on chromosome 2 in a paternity test and aims to provide a definitive identification opinion. STR genotyping was performed using the AGCU Expressmarker 22, Goldeneye DNA Identification System 22NC, and AGCU X Plus STR kits. Additionally, chromosomal microarray analysis (CMA) was used to assess copy number variations and regions of homozygosity (ROH). The cumulative paternity index based on 21 autosomal STR loci (AGCU Expressmarker 22) was 8.4361E-04. When combined with the 39 STR loci from the Goldeneye System, the index increased to 3.1806E + 04. All discordant loci-D2S441 and D2S1338-were located on chromosome 2, where the alleged father had genotypes 11,11.3 and 17,19, respectively, while the child had 14,14 and 24,24. The TPOX locus (also on chromosome 2) showed homozygosity (8,8) in the child. X-STR analysis confirmed that the alleged father contributed all necessary alleles. CMA revealed a 243.03 Mb ROH spanning 2p25-q37.3 in the child, suggesting identity by descent or uniparental disomy. These findings highlight the potential for chromosomal anomalies to mimic false exclusions in paternity testing. Comprehensive genetic analysis is recommended when inconsistencies arise at multiple loci on the same chromosome.