Genetic Counselling Pitfall: Co-Occurrence of an 11.8-Mb Xp22 Duplication and an Xp21.2 Duplication Disrupting .

We report a 3-generation family in which 2 Xp copy number variations (CNVs) co-segregate. The proband presented with syndromic intellectual disability. The CNV had been revealed by conventional karyotyping, identifying a large Xp22 duplication causing an Xp functional disomy. Family studies found that this duplication was inherited from the proband's mother and was also present in one of his sisters. This sister had conventional karyotyping performed during pregnancy with a normal result. Postnatally, her child, the proband's nephew, presented with autism spectrum disorders. aCGH revealed a 339-kb duplication. Overall, the proband, his mother, and one of his sisters all harboured both CNVs, while his other sister and the 2 sons of each sister only carried the intragenic duplication. As seen in this family, we emphasise the importance of small CNV detection, the pathogenicity of exonic duplications in male carriers, and the difficulties for genetic counselling with the risk of double diagnosis in a single patient.