Familial transmission of chromoanagenesis leads to unpredictable unbalanced rearrangements through meiotic recombination

Chromoanagenesis is a cellular mechanism that leads to complex chromosomal rearrangements (CCR) during a single catastrophic event. It may result in loss and/or gain of genetic material and may be responsible for various phenotypes. These rearrangements are usually sporadic. However, some familial cases have been reported. Here, we studied six families in whom an asymptomatic or paucisymptomatic parent transmitted a CCR to its offspring in an unbalanced manner. The rearrangements were characterized by karyotyping, fluorescent in situ hybridization, chromosomal microarray (CMA) and/or whole genome sequencing (WGS) in the carrier parents and offspring. We then hypothesized meiosis-pairing figures between normal and abnormal parental chromosomes that may have led to the formation of new unbalanced rearrangements through meiotic recombination. Our work indicates that chromoanagenesis might be associated with a normal phenotype and normal fertility, even in males, and that WGS may be the only way to identify these events when there is no imbalance. Subsequently, the CCR can be transmitted to the next generation in an unbalanced and unpredictable manner following meiotic recombination. Thereby, prenatal diagnosis using CMA should be proposed to these families to detect any pathogenic imbalances in the offspring.

Prenatal Diagnosis of Trisomy 2p due to Terminal 2p Duplication including Interstitial Telomeric Sequences

We report on a prenatally diagnosed unusual case of inverted terminal duplication of the short arm of chromosome 2, leading to interstitial telomeric sequences (ITSs) and partial trisomy 2p. To our knowledge, there are only 4 further cases of pure partial trisomy 2p reported prenatally. Here, the mother was referred at 22 weeks of gestation for isolated fetal congenital heart malformation at ultrasound. The karyotype of amniotic fluid cells displayed a large duplication of the short arm of chromosome 2 that was further investigated by array-CGH, which detected a 1-copy gain of 43.75 Mb in chromosome 2 at 2p21p25.3. FISH confirmed the presence of an inverted duplication in the short arm of chromosome 2 involving the region 2p21pter and revealed the presence of ITSs at the breakpoint in chromosome 2p21. This report contributes to the prenatal description of the syndrome. We also discuss the possible mechanisms leading to this duplication and the formation of ITSs which are rarely described in constitutional rearrangements.