Maternal age and the parental origin of trisomy 21 in Libyan individuals with Down syndrome: a preliminary familial D21S11 STR study

Abstract Down syndrome (DS) is the most prevalent chromosomal disorder worldwide and is primarily caused by chromosome 21 nondisjunction (Ch21 NDJ). Categorizing trisomy 21 cases by parental origin allows a more precise assessment of maternal age (MA) as a DS risk factor. This study aimed to investigate the association between MA and parental allele transmission patterns at the D21S11 locus in individuals with DS. A familial-based study was conducted by collecting blood samples from 55 DS Libyan families, categorizing into two groups based on MA (<35 years and ≥35 years). Short tandem repeat analysis of D21S11 marker on Ch21 was used to trace allelic transmission from parents to offspring. The parental NDJ errors were traceable in 24 (58.5%) of 41 informative families, with maternal and paternal NDJ errors accounting for 20/24 (83.3%) and 4/24 (16.7%), respectively. Given the limited traceability rate, this investigation should be considered a preliminary study. Among the 24 informative cases, maternal-origin trisomy accounted for 8 of 10 cases (80.0%) in mothers aged <35 years and 12 of 14 cases (85.7%) in mothers aged ≥35 years. The present results suggest that MA may be associated with the distribution of trisomy 21 based on D21S11 parental allele transmission patterns; however, no statistically significant association was detected in the present cohort ( P = 0.563). Although additional Ch21 markers are needed, this study provides preliminary insights into MA-related patterns of allele transmission in Libyan individuals with DS.