Down syndrome in Eastern Libya: Cytogenetic subtypes, age at diagnosis, and maternal age in a five-year series

Down syndrome is the most common autosomal aneuploidy, but its cytogenetic subtypes and the age at which it is diagnosed have not been well described for eastern Libya. This study characterized the Down syndrome cases within a five-year cytogenetic registry, with attention to subtype distribution, age at diagnosis, and maternal age. This study analyzed the Down syndrome cases identified among all karyotype referrals to the Genome Laboratory, Benghazi, in 2021-2025, the subset of a 319-record registry whose overall cytogenetic profile is reported separately. Karyotypes were classified per ISCN as free trisomy 21, translocation, or mosaic. Maternal age was compared between Down syndrome and other referred patients using the Mann-Whitney U-test; proportions are given with 95.0% confidence intervals (CIs). 58 patients had Down syndrome (23.1% of 251 karyotyped referrals; 31 male, 27 female). Free trisomy 21 accounted for 54 cases (93.1%; 95.0% CI 83.6-97.3), translocation for three (5.2%), and mosaicism for one (1.7%). Diagnosis was early: The median age at karyotyping was 0.10 years (about five weeks), and 50 of 56 patients with a recorded age (89.3%) were diagnosed before their first birthday. The median maternal age was 37.0 years (interquartile range 31-41), with 58.6% of mothers aged 35 years or older; maternal age was higher than among other referred patients (median 31.0 years; p = 0.008). The subtype distribution matched international and earlier Libyan data and differed from a recent Benghazi series that reported markedly higher mosaicism. Thus, in eastern Libya, Down syndrome is predominantly free trisomy 21, is strongly associated with advanced maternal age, and, unlike the sex-chromosome aneuploidies, is recognized early, usually within the first year of life. These findings support maternal-age-based counseling while indicating that neonatal recognition of trisomy 21 is already effective locally.