Fragile X syndrome in a girl with variant Turner syndrome and an isodicentric X chromosome

Fragile X (FXS) and Turner (TS) syndromes are X-chromosome-associated disorders. Herein, we report the case of a girl in middle childhood with bicuspid aortic valve in infancy, growth failure, global developmental delay (GDD), visual problems, and coexisting attention-deficit/hyperactivity and anxiety disorders. A high-resolution karyotype in 20 cells revealed 46,X,Idic(X)(p11.21)[19]/45,X[1], suggestive of variant TS. Given her atypical phenotype, subsequent DNA testing was performed. Four FMR1 cytosine-guanine-guanine repeats (30, 410, 580 and 800) were identified, confirming the additional FXS diagnosis. This case study highlights the importance of additional genetic testing in individuals with atypical variant TS, such as unexplained GDD and distinct facial characteristics. The additional FXS diagnosis prompted new therapeutic development for the patient to advance precision healthcare.