Non‐mosaic partial tetrasomy and partial trisomy 9

Partial tetrasomy 9 is a very rare chromosome abnormality. Of the reported cases, most have had tetrasomy only of 9p arising from the formation of an isochromosome. In addition, mosaicism was found in five of the 12 previous cases. We report on a case of non-mosaic partial tetrasomy 9 involving all of the short arms and asymmetrical segments of the long arms.