Context: The fragile X syndrome is characterized by intellectual deficit and some physical characteristics, which become more evident during growth, especially craniofacial and macroorchidism. Case report: A 22 year-old male patient with diabetes mellitus type 1 (DM1) diagnosed at 7 years of age is following-up with ophthalmology due to low visual acuity. On physical exam, he did not maintain eye contact and performed repetitive movements. In addition, he had an elongated face and upward

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... g eyelid clefts, a high palate and prognathism, large and prominent ears. In the family history, 3 of his siblings, one male and two female, also had intellectual deficit, and two of them had concomitant DM1. One brother had only DM1 and the other none of the diseases. The parents had consanguinity (they were cousins in the 3rd degree). The patient's karyotype, using the chromosomal breaks technique after cultivation in medium-low folic acid, showed the presence of fragility on the X chromosome in the region q27.3 [46, XY, fra (x) (q27.3)], compatible with the diagnosis of fragile X syndrome. This result was confirmed using the PCR-multiplex technique. Conclusions: In this family, the concomitant presence in several individuals of the fragile X syndrome and DM1 stands out. However, although both conditions are not related, they are frequent, which could justify their simultaneous occurrence.