Tetrasomie 18p

Tetrasomy 18p is a rare chromosomal disorder. The phenotype results from the presence of a small extra metacentric marker chromosome, an isochromosome 18p. The syndrome is characterized by mild to moderate mental retardation, microcephaly, minor dysmorphic features and spasticity of the lower limbs. Here we report on a 2-year-old girl, who was referred because of developmental delay and minor dysmorphic signs. Cytogenetic investigations revealed a small supernumerary marker chromosome. Further analysis using spectral karyotyping (SKY?) and fluorescence in situ hybridization (FISH) identified the marker chromosome fragment as an isochromosome 18p.