[Genetic origin analysis of regions of homozygosity in three cases].

OBJECTIVE:To explore the genetic characteristics of three fetuses with regions of homozygosity (ROH). METHODS:Three fetuses with ROH diagnosed at Nanjing Drum Tower Hospital on December 2, 2020, March 19, 2021, and May 27, 2022, respectively were selected as the study subjects. Clinical data of the fetuses were collected. Chromosomal microarray analysis (CMA) was used to detect the ROH, and tandem repeat sequences (STR)-based multiplex PCR assay was used to identify the mosaicism status in fetus 1. RESULTS:Partial maternal isodisomy (iUPD) (16) was found in fetus 1, for which trisomy rescue may be accountable. Meanwhile, the fetus also has confined placental mosaicism (CPM) but not true mosaicism. The formation mechanism of ROH for fetus 2 was identity by descent. Partial maternal iUPD (7) was found in fetus 3, which may be due to gametic recombination. CONCLUSION:The ROH of the three fetuses were inherited from both parents or the mother. Above findings suggested that it is justified to detect ROH on imprinting disorder-related chromosomes when potential uniparental disomy is suspected.