Delineation of two distinct 6p deletion syndromes

Deletions of the short arm of chromosome 6 are relatively rare, the main fe atures being developmental delay, craniofacial malformations, hypotonia, an d defects of the heart and kidney, with hydroccphalus and eye abnormalities occurring in some instances. We present the molecular cytogenetic investig ation of six eases with 6p deletions and two cases with unbalanced transloc ations resulting in monosomy of the distal part of 6p. The breakpoints of t he deletions have been determined accurately by using 55 well-mapped probes and fluorescence in situ hybridization (FISH). The cases can be grouped in to two distinct categories: interstitial deletions within the 6p22-p24 segm ent and terminal deletions within the 6p24-pter segment. Characteristics co rrelating with specific regions are: short neck, clinodactyly or syndactyly , brain, heart and kidney defects with deletions within 6p23-p24; and corne al opacities/iris coloboma/Rieger anomaly, hypertelorism and deafness with deletions of 6p25, The two cases with unbalanced translocations presented w ith a Larsen-like syndrome including some characteristics of the Gp deletio n syndrome, which can be explained by the deletion of 6p25. Such investigat ion of cytogenetic abnormalities of 6p using FISH techniques and a defined set of probes will allow a direct comparison of reported cases and enable m ore accurate diagnosis as well as prognosis in patients with 6p deletions.