Clinical Outcome: A Monosomy 18p is Better than a Tetrasomy 18p

We report the clinical and laboratory data of 2 patients with different rearrangements involving the short arm of chromosome 18, one with an isochromosome 18p (tetrasomy 18p) and the other with an 18p deletion (monosomy 18p by translocation t(15;18)). Based on molecular cytogenetic findings including high-resolution SNP array, FISH, and multiplex fluorescence PCR, we compared the clinical phenotypes of the 2 patients with other reported patients with 18p deletion, trisomy 18, and isochromosome 18p syndromes to obtain genotype/phenotype correlations. Our findings suggest that a partial monosomy 18p has the better clinical outcome than a tetrasomy 18p.