COL18A1 and Down syndrome: This latter model recapitulates the clinical observation that patients with Down's syndrome (trisomy 21) who have three copies of the collagen XVIII gene and 70% higher serum endostatin levels (Zorick et al, 2001) have much lower standardised mortality odds ratios for death from solid malignant tumours at all ages than the rest of the population (Yang et al, 2002), suggesting that endostatin may have an endothelium-specific tumour suppressor function in humans.