Pallister-Killian Syndrome: The Diagnosis is in the Detail

Introduction

Pallister-Killian syndrome (PKS; OMIM 601803) was first described in 1977 by the American physician Philip Pallister and later in 1981 by the Austrian physician Wolfgang Killian. PKS is a rare chromosomal disorder due to a sporadic mosaic tetrasomy of the short arm of isochromosome 12 (i12p). Hexasomic forms (2 isochromosomes) or the presence of a ring chromosome have been described. Prenatal ultrasound may show polyhydramnios, rhizomelic micromelia or macrosomia (Lloveras E et al., Fetal Diagn Ther 2013; 34: 172–175). Main clinical features in the newborn are hypotonia, feeding difficulties, pigmentary skin anomalies and seizures but physical head exam may give the clue for diagnosis. Hypertelorism, small nose, long philtrum, V-shaped upper lip (“Pallister lip”), low set posteriorly rotated ears, bilateral frontotemporal alopecia and a coarse facies (more pronounced with age) are characteristic for PKS. Further congenital cardiac defects, diaphragmatic hernia, renal or anal malformations may be associated. A phenotypical study of 22 PKS patients showed that profound intellectual disability is not universal, a considerable percentage of patients presented mild or moderate disability (Blyth M et al., J Med Genet 2015; 52: 454–464). Increased maternal age is an independent risk factor for PKS. i12p can be detected prenatally in chorionic villus and amniotic fluid cell samples or later in lymphocytes and skin fibroblast cultures. No evidence of genotype-phenotype correlation was found in PKS (Doray B et al., Prenat Diagn 2002; 22: 470–477). We describe a clinical case of PKS in a late premature patient without prenatal diagnosis. The mother has given written consent for the publication.