Multiple Aneuploidy: First Report of a Patient Presenting with a Karyotype 45,X/48,XXX,+21.

Introduction: The dual diagnosis of Down syndrome and Turner syndrome in the same patient was clinically identified in the early 1950s before the development of karyotyping techniques. After that, several authors reported anecdotal patients and/or reviewed series of Down-Turner double aneuploidies due to a regular 46,X,+21 constitution or different combinations of abnormal cell lines. In such cases, the most typical presentation encompasses the female sex, Down syndrome phenotype, and chromosomal mosaicism.

Case presentation: Here we report a female patient presenting with short stature, dysmorphic features, developmental delay, and learning disabilities, whose karyotype revealed a previously undescribed 45,X[47]/48,XXX,+21[3] constitution.

Conclusion: This is the first case encompassing these three aneuploidies together and, contrary to most previous reports, exhibiting a predominantly Turner syndrome phenotype associated with developmental delay.