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Proliferative vasculopathy and hydranencephaly-hydrocephaly syndrome (PVHH; MIM 225790) is an autosomal recessive perinatal lethal condition due to mutations in the gene encoding the feline leukemia virus subgroup C receptor 2 (FLVCR2). This disorder is characterized by a glomeruloid, proliferative vasculopathy within the brain parenchyma and in many instances in the spinal cord, resulting in hydrocephaly, hyrdranencephaly (absence of cerebral hemispheres replaced by fluid filled sacs) and severe ventriculomegaly. Associated central nervous system findings may include cerebellar hypoplasia, a hypoplastic brain stem, agenesis of the corpus callosum, cortical thinning and calcifications in the white matter, basal ganglia, brainstem, cerebellum and spinal cord. Intrauterine growth retardation, macrocrania, severe arthrogryposis, pterygia, decreased fetal movements and muscular hypoplasia, cystic hygroma, cleft palate and microretrognathia have also been reported. Diagnosis is usually made by ultrasound between 23 and 33 weeks of gestation. The FLVCR2 gene product is a transmembrane protein thought to be involved in calcium ion transport. It is thought that disrupted calcium homeostasis results in the central nervous system proliferative vasculopathy, which ultimately causes hemorrhagic necrosis within the CNS and some of the secondary effects noted above.