Supplementary Material for: CLINICAL CHARACTERIZATION AND CYTOGENETIC-MOLECULAR STUDY OF A PATIENT WITH A RING CHROMOSOME 12

Introduction: Ring chromosomes generally result from the fusion of breaks at the ends of both arms of a chromosome, typically leading to the loss of genetic material from these ends. Case Presentation: We report the case of a four-year-old patient who exhibits multiple café-au-lait spots, hypochromic spots, bitemporal narrowing, bilateral epicanthus, patent foramen ovale, and multiple brain abnormalities identified through magnetic resonance imaging. Karyotyping revealed a ring chromosome: r(12). Chromosomal microarray analysis revealed a ~3.6 Mb deletion in the short arm and a ~1.2 Mb deletion in the long arm of chromosome 12. The patient's phenotype is consistent with these genetic imbalances. To investigate ring chromosome instability and mosaicism, 200 metaphases were analyzed using G-banding and FISH with a whole chromosome painting probe, identifying 166 cells with a 46,XX,r(12) karyotype, 20 cells with monosomy 12, eight with a dicentric ring chromosome, three with two monocentric rings, two with two interlocked dicentrics, and one with an open ring chromosome. Conclusion: This study provided a detailed characterization of the ring rearrangement of chromosome 12, the first with SNP-array, enhancing the understanding of its genetic and phenotypic implications, and contributing to expanding knowledge about this condition. Additionally, the findings can aid in better understanding the patient’s prognosis, clinical follow-up, and genetic counseling.