[Trisomy 20 mosaicism revealed by pigmentary mosaicism of the Ito-type].

INTRODUCTION: Ito hypomelanosis-type pigmentary mosaicism is characterized by congenital pigmentation disorders along Blaschko's lines. We report a case of Ito-type pigmentary mosaicism associated with a congenital growth hormone deficiency having revealed trisomy 20 mosaicism.

OBSERVATION: A 4 year-old boy presented with congenital pigmentation disorders. His history was marked by: inter-uterine delayed growth of unknown etiology, a dysmorphic syndrome, psychomotor retardation with speech problems, right cryptorchidia and an isolated, idiopathic, congenital growth hormone deficiency that had been treated with recombinant somatropine since the age of three. The clinical examination revealed alternating hypo and hyper-pigmented maculae with linear distribution on the limbs and in "twirls" on the trunk following Blaschko's lines. The blood karyotype was normal, the karyotype on fibroblasts of hypopigmented skin revealed trisomy 20 mosaicism.

DISCUSSION: The occurrence of pigmentary mosaicism related to trisomy 20 mosaicism is exceptional. The combination of Ito hypomelanosis-type pigmentary mosaicism and delayed growth due to growth hormone deficiency has never been reported before. Our observation, unusual because of such an association, raises the question of the eventual existence of associated genes located on the chromosome 20 implied in the secretion of growth hormone and/or melanogenesis. It also underlines the interest of conducting cytogenic explorations on fibroblasts of damaged skin in the case of Ito-type pigmentary mosaicism, even if the blood karyotype is normal or in the absence of a patent phenotype abnormality.