Editor—In the March 1999 issue of the journal, Portnoi et al 1 reported a patient with hyperpigmentation distributed along the lines of Blaschko2 3 with mosaicism for partial tetrasomy for the chromosomal region 3q27-q29. Here we describe a patient who displays a very similar pattern of skin hyperpigmentation (fig 1A, B) associated with mosaicism for a small partial terminal triplication of 3q (fig 2) leading to functional tetrasomy with the following karyotype obtained from lymphocytes: mos 46,XY, trp(3)(q27.1-qter)[47]/46,XY[4]. Both parents were found to have a normal karyotype. The proband is a 5 year old boy, the first child of healthy, unrelated parents. During early pregnancy intrauterine growth retardation was suspected, but no anomalies were recorded during the following months except reduced fetal movements. He was born by caesarean section 3 weeks before the calculated date of birth because of HELLP syndrome. His birth weight and length were 2810 g and 49 cm, respectively. Owing to his pigmentary skin anomalies, soon after birth the diagnosis of a hypomelanosis of Ito was made. He was retarded in all developmental milestones, as he was not able to sit before …