Hypomelanosis of Ito in a girl with Trisomy 13 mosaicism: a cytogenetic study

BACKGROUND: Hypomelanosis of Ito was first described by Ito in 1952 as incontinentia pigmenti achromians. The consistent feature of the disease is a characteristic cutaneous hypopigmentation area following the lines of Blaschko, but the clinical manifestations are varied and hypomelanosis of Ito is regarded as a neurocutaneous syndrome. Hypomelanosis of Ito is sporadic but is probably a non-specific expression of chromosomal mosaicism; we report a case with four clones. CASE REPORT: We report the case of a 26 year-old woman with neurocutaneous hypomelanosis of Ito and Trisomy 13 mosaicism. She also exhibited skeletal and ophthalmologic disorders. Immunohistology revealed a PS100 and Melan A decrease in hypopigmented skin. Cytogenetic study of normal and hypopigmented skin fibroblasts showed mosaicism with four clones. DISCUSSION: This is the third case of Trisomy 13 mosaicism associated with hypomelanosis of Ito, although other anomalies on chromosome 13 have been described. Happle published "phylloid" pigmented cases, which are mainly associated with Trisomy 13. This is the first observation of four-clone mosaicism and can be explained by successive mutations during embryogenesis. Anomalies on chromosomes 5,6 and 21 have never been described. The definition of hypomelanosis of Ito is not well established and the disease is presently included in a group of "pigmentary dysplasia" with genetic mosaicism.