Mosaic trisomy 12 – A case of a rare phenotypic association and literature review

Introduction

Mosaicism is a phenomenon when a single fertilized egg develops into an embryo comprising two or more cell clones, each with a unique genotype. Mosaic trisomy 12 is a rare condition with a very variable phenotype. Confirmation of the diagnosis is difficult due to the different ratios and distribution of mosaic cells, various affected tissues, false-negative results and presence of extraembryonic mosaicism.

Case presentation

In this study, we report a patient with developmental delay, brain anomalies (mega cisterna magna, hypoplastic corpus callosum and hypophyseal fossa), chorioretinal pigmentary dysplasia, congenital heart disease, bilateral cryptorchidism, hydronephrosis, and dysmorphic features associated to a trisomy 12 mosaicism.

Discussion

The manifestation of trisomy 12 mosaicism is multisystemic, and the most frequent finding is dysmorphic features. Other common findings are developmental delay, congenital heart disease, gastrointestinal system malformations, skeletal anomalies, and hypotonia. Fluorescence in situ hybridization analysis, array comparative genomic hybridisation or single nucleotide polymorphism array are being proposed as first-tier methods for diagnosing mosaic trisomy 12.

Conclusion

This study expands the phenotypic spectrum associated with this rare condition. Detailed investigation allows individualized care of patients with trisomy 12 mosaicism.