Gene PKD2 is identified, using genetic linkage study, on chromosome 4. A group of voltage-linked cation channels, with inward selectivity for K>Na>>Ca and outward selectivity for Ca2+ ≈ Ba2+ > Na+ ≈ K+, are coded for by PKD2 on chromosome 4. PKD3 recently appeared in research papers as a postulated third gene. Fewer than 10% of cases of ADPKD appear in non-ADPKD families. Cyst formation begins in utero from any point along the nephron, although fewer than 5% of nephrons are thought to be involved. As the cysts accumulate fluid, they enlarge, separate entirely from the nephron, compress the neighboring kidney parenchyma, and progressively compromise kidney function. Autosomal recessive
Autosomal recessive polycystic kidney disease (ARPKD) (OMIM #263200) is the less common of the two types of PKD, with an incidence of 1:20,000 live births and is typically identified in the first few weeks after birth. Unfortunately, the kidneys are often underdeveloped resulting in a 30% death rate in newborns with ARPKD. PKHD1 is involved. Mechanism
Both autosomal dominant and autosomal recessive polycystic kidney disease cyst formation are tied to abnormal cilia-mediated signaling. The polycystin-1 and polycystin-2 proteins appear to be involved in both autosomal dominant and recessive polycystic kidney disease due to defects in both proteins.
Pulmonary capillary hemangiomatosis (PCH) is a disease affecting the blood vessels of the lungs, where abnormal capillary proliferation and venous fibrous intimal thickening result in progressive increase in vascular resistance. It is a rare cause of pulmonary hypertension, and occurs predominantly in young adults. Together with pulmonary veno-occlusive disease, PCH comprises WHO Group I causes for pulmonary hypertension. Indeed, there is some evidence to suggest that PCH and pulmonary veno-occlusive disease are different forms of a similar disease process. Presentation
These are non specific. Typical symptoms include dyspnea, cough, chest pain and fatigue. Genetics
At least some cases appear to be due to mutations in the eukaryotic translation initiation factor 2-alpha kinase 4 (EIF2AK4) gene. Diagnosis
Lung biopsy is essential to make this diagnosis. This can be difficult if the pulmonary pressure is high. Investigations
Chest X ray may show enlargement of the heart and ill-defined patchy lesions in the lung fields. CT chest typically shows wide spread ill-defined centrilobular nodules of ground glass opacity. This is a nonspecific finding and may be seen in a number of pulmonary diseases. CT pulmonary angiography usually shows enlargement of the main pulmonary artery. When measured by echocardiography or pulmonary angiography, the pulmonary arterial pressure is typically elevated. Differential diagnosis
Pulmonary veno-occlusive disease

Associations
This condition has been reported in patients with Ehlers Danlos syndrome, CREST syndrome and scimitar syndrome. Treatment
The only definitive treatment for this condition currently is lung transplantation. Median survival without treatment is 3 years.Imatinib may be of use.Epoprostenol does not appear to be of use.