<i>De novo</i> meiotic recombination of chromosome 18q21.33q22.3 and 18q22.3q23 results in different chromosomal abnormalities among siblings with developmental and speech delay

Introduction We report on two siblings with mild developmental and speech delay carrying different interstitial duplications of the long arm of chromosome 18 inherited from an affected mother. Results The proband is an adult woman with a history of developmental delay as a child. Both karyotyping and chromosomal microarray revealed interstitial duplications of the segment between bands 18q21.3 and 18q23 at breakpoint 18q23. Variable clinical phenotypes such as developmental delay, intellectual disability and microcephaly have been reported in DECIPHER with similar duplications. The youngest son, with developmental and speech delay, inherited both duplications from the mother, while the elder daughter only inherited the 18q22.3q23 duplication. The different chromosomal abnormalities between the siblings are accounted by a de novo recombination with the breakpoint located between genomic positions 69341773 (rs8084188) and 69396486 (rs1505743), indicating the intrachromosomal rearrangement of chromosome 18. Conclusion We reported a case of a de novo recombination of chromosome 18q21.33q22.3 leading to different chromosomal abnormalities between the siblings. Maternal chromosome rearrangement detected by non-invasive prenatal test should not be considered as the only aspect; it could also open a gateway for genetic counselling to pregnant women carrying previously unknown de novo recombinations or chromosomal rearrangements.