Hypomelanosis of Ito vs Pigmentary Mosaicism: a challenging diagnosis

Introdution: Since 1952 several case reports and case series of Hypomelanosis of Ito (HI) has described different associations with multiple extra cutaneous manifestations, being the neurological anomalies the most frequent and important ones. Methods: We report a 5-years-old girl, refered by dyschromia , minor dysmorphic features, strabism, ventricular septal heart defect and slight learning difficulties. The peripheral blood karyotype that was normal. Hypopigmented patches along Blaschko’s lines were observed. Other anomalies included a simian palm crease on right hand, persistency of fetal pads, and mild genu valgum/recurvatum. A skin biopsy for histopathological and cytogenetic studies was performed on a hypopigmented patch and a magnetic resonance imaging (MRI) of central nervous system (CNS) was requested. Results: Histopathological study of the skin was inconclusive. However, the cytogenetic study revealed the presence of mosaicism: one normal cell line and one abnormal cell line with monosomy of chromosome 18 and presence of a marker chromosome (46,XX,-18,+mar[22]/46,XX[28]) . Fluorescence in situ hybridization (FISH) technique identified the marker as a derivative of chromosome 18, comprising the centromeric region and a small portion of euchromatic material. CNS MRI was normal. Discussion: Some authors suggest that HI would be better designated as “pigmentary mosaicism”, following the hypothesis that the chromosomal abnormalities reported specifically disrupt pigmentary genes. Although numerous cases of mosaicism concerning chromosome 18 were previously described, this specific cytogenetic anomaly was not yet reported. The mild phenotype presented in this case suggests that mosaicism may have a low expression. Nevertheless, the loss genetic material in the abnormal cell line raises several questions about future outcomes, especially regarding the theoretical concern of a predisposition to certain malignancies and the difficulty of genetic counseling. This case illustrates the challenge of a diagnosis when facing a variety of phenotypes and reinforces the importance of karyotyping other tissues besides peripheral blood