Phylloid hypomelanosis is closely related to mosaic trisomy 13.

Phylloid hypomelanosis is a distinct type of pigmentary mosaicism characterized by congenital hypochromic macules resembling a floral ornament with various elements such as round or oval patches, macules resembling the asymmetrical leaves of a begonia, or oblong lesions. A review of cases with documentation of cytogenetic findings showed that aberrations involving chromosome 13 were present in 5 out of 6 patients. Examination of blood lymphocytes revealed a 46, XX/47 XX, +13 or 46, XX/47, XX, +der (13) mosaic in three of these cases and a karyotype 46, XX, t(13;13) in the other two cases. Cytogenetic analysis of skin fibroblasts showed chromosomal mosaicism in 4 of the 5 patients. In the remaining case, a chromosome 13 translocated on 13 was found in 100% of blood lymphocytes and skin fibroblasts, suggesting that mosaicism involving chromosome 13 may have developed in the melanocyte system. In conclusion, contrasting with hypomelanosis of Ito which is a cutaneous sign of many different states of mosaicism, phylloid hypomelanosis seems to originate preponderantly from a mosaic state involving chromosome 13. Future case reports may help to delineate further the significance of this relationship.