Alveolar capillary dysplasia with misalignment of the pulmonary veins (ACD/MPV) is a rare developmental lung disorder of neonates and infants. When a person breathes, air enters the lungs and fills tiny air sacs called alveoli. Each alveoli is surrounded by a capillary bed, which is a network of tiny, thin blood vessels. In order for oxygen and carbon dioxide to be exchanged during breathing, the alveoli and capillaries must be properly aligned. If there are not enough capillaries or the capillaries are too far away from the surface of the alveoli, gas exchange cannot occur effectively. This means there is not enough oxygen for the body and the heart must work much harder. Alveolar Capillary Dysplasia is a disorder where the capillaries around the alveoli fail to develop normally. In ACD/MPV, fewer capillaries are present and those that are present are not positioned correctly within the walls of the alveoli. This results in very difficult and ineffective gas exchange.
ACD/MPV is one of the most common of the interstitial lung diseases of childhood. ACD/MPV produces respiratory failure early in life and carries a high mortality rate. Infants with ACD/MPV develop severe breathing problems and lack of oxygen in the blood (hypoxemia). Normally, blood is brought to the capillaries by arteries, and the veins carry blood away from the alveoli to the heart with lymph vessels. In ACD/MPV patients, these veins are abnormally misaligned with the arteries. The smooth muscle tissue in the arteries is often thickened, which restricts normal blood flow. When this occurs, it increases the blood pressure in the pulmonary arteries which causes pulmonary hypertension one of the main symptoms of this disease. Breathing becomes progressively worse and most infants experience respiratory failure.
The primary clinical focus for ACD/MPV has been on early recognition and accurate diagnosis to avoid invasive and ineffective interventions for patients and their families. Advances in understanding of the genetics, pathology, and clinical features of the disease have revealed a potentially higher prevalence than originally thought. Reports of infants presenting with symptoms of ACD/MPV beyond the neonatal period have also begun to emerge. This offers the possibility that milder forms of the disease may exist. DNA sequencing and comparative genomic hybridization have led to the identification of FOXF1 as one of the genes responsible for ACD/MPV. This has allowed for limited noninvasive diagnostic testing in some infants.
There have been more than 100 cases of ACD/MPV reported worldwide but still the incidence or prevalence of ACD/MPV is not yet known. There may be more cases of ACD/MPV than those that have been formally reported. A definitive diagnosis of ACD/MPV currently depends on an examination of lung tissue on autopsy or ante mortem lung biopsy and neither of these diagnostic modalities is universally pursued. Another reason is that many infants born with ACD/MPV have associated malformations in other organ systems. This may allow the lung pathology to go undetected. It is also possible that the diagnosis may be missed by pathologists unfamiliar with the disorder.
For rare diseases such as ACD/MPV progress and understanding depends on the identification of new cases and increasing awareness among health-care providers. Advances in ACD/MPV genetics research, with support from federal health-related research agencies, are providing an impetus for continued investigation into several aspects of this rare disease.