Multicolor-FISH Characterization of a Prenatal Mosaicism for a Chromosomal Rearrangement Undetected by Molecular Cytogenetics

Fetal mosaicism for chromosomal rearrangements remains a challenge to diagnose, even in the era of whole-genome sequencing. We present here case fetal rearrangement explored amniocytes and muscle, consisting major cell population (95%) with partial monosomy 4q minor (5%) additional material replacing 4qter deleted segment. Molecular techniques (MLPA, array-CGH) failed assess origin this material. Only multicolor-FISH identified segment on chromosome 4 as derived from 17. Due poor prognosis, couple chose terminate pregnancy. Because low-level mosaicism, microarray analysis (CMA), now considered first-tier prenatal genetic analysis, did not allow identification line. In large CNVs (>5 Mb) detected by CMA, karyotyping may be elucidate mechanism underlying eliminate mosaicism.