B3GALNT2 and Hydrocephalus: In the current study, no genetic heterogeneity was observed for hydrocephalus with all 16 affected Friesian horses being homozygous for the same nonsense mutation in B3GALNT2. The strongest indication that this mutation causes the phenotype in Friesian horses is that the exact same nonsense mutation was found homozygously in a human muscular dystrophy patient with hydrocephalus by Stevens et al. [30] (Fig. 5) [MIM:610194.0006 or dbSNP:rs367543077].