Identification of Prostaglandin I2 Synthase Rare Variants in Patients With Williams Syndrome and Severe Peripheral Pulmonary Stenosis

BACKGROUND

Peripheral pulmonary stenosis (PPS) is a condition characterized by the narrowing of the pulmonary arteries, which impairs blood flow to the lung. The mechanisms underlying PPS pathogenesis remain unclear. Thus, the aim of this study was to investigate the genetic background of patients with severe PPS to elucidate the pathogenesis of this condition.

METHODS AND RESULTS

We performed genetic testing and functional analyses on a pediatric patient with PPS and Williams syndrome (WS), followed by genetic testing on 12 patients with WS and mild-to-severe PPS, 50 patients with WS but not PPS, and 21 patients with severe PPS but not WS. Whole-exome sequencing identified a rare PTGIS nonsense variant (p.E314X) in a patient with WS and severe PPS. Prostaglandin I2 synthase (PTGIS) expression was significantly downregulated and cell proliferation and migration rates were significantly increased in cells transfected with the PTGIS p.E314X variant-encoding construct when compared with that in cells transfected with the wild-type PTGIS-encoding construct. p.E314X reduced the tube formation ability in human pulmonary artery endothelial cells and caspase 3/7 activity in both human pulmonary artery endothelial cells and human pulmonary artery smooth muscle cells. Compared with healthy controls, patients with PPS exhibited downregulated pulmonary artery endothelial prostaglandin I2 synthase levels and urinary prostaglandin I metabolite levels. We identified another PTGIS rare splice-site variant (c.1358+2T>C) in another pediatric patient with WS and severe PPS.

CONCLUSIONS

In total, 2 rare nonsense/splice-site PTGIS variants were identified in 2 pediatric patients with WS and severe PPS. PTGIS variants may be involved in PPS pathogenesis, and PTGIS represents an effective therapeutic target.

Pernicious Anemia in an Adult with Trisomy 21

Pernicious anemia is an autoimmune disease caused by the malabsorption of vitamin B12. It usually appears in the elderly. People with trisomy 21 are susceptible to autoimmune diseases. This susceptibility is thought to be due to altered expression of the AIRE gene, which is located in the 21q22.3 region. Although pernicious anemia is not common in people with trisomy 21, AIRE is pointed out as a susceptibility gene of pernicious anemia in a genome-wide association study. Here, we report a man with trisomy 21, who suffered from the pernicious anemia. When he was in his 30 s, he visited our hospital because of diarrhea and poor oral intake. He showed thrombocytopenic purpura-like features, and was diagnosed as pernicious anemia. After supplementation of vitamin B12, he recovered from the illness. The reason for his early onset may be because of trisomy 21. Altered expression of AIRE might trigger the disease.

A Cardiac Arrest Case due to Left Coronary Artery Compression in Congenital Heart Disease-Associated Pulmonary Arterial Hypertension

We report the case of an adult who had a cardiac arrest in the setting of pulmonary hypertension and a previously repaired intermediate atrioventricular septal defect, with left main coronary trunk stenosis due to dilatation of the main pulmonary artery. In patients with pulmonary hypertension exhibiting anginal symptoms, it is advisable to perform chest contrast computed tomography to confirm the pulmonary artery diameter and the presence of coronary artery compression. In addition, our case highlights the importance of early collaboration among specialists during the transition from adolescence to adulthood.

A rare nonsense variant of the X-gene in a paediatric patient with severe peripheral pulmonary stenosis

Background

Most cases of peripheral pulmonary stenosis (PPS) associated with William's syndrome are usually very mild or resolve spontaneously. However, we encountered a paediatric case of William's syndrome (WS) with severe PPS. In this case, we investigate whether the patient's genetic background was responsible for the severity of the PPS.

Case presentation

Shortly after birth, the male patient was suspected as WS because of his peculiar facial appearance and PPS. Fluorescence in situ hybridization identified microdeletion in the 7q11.23 region, and he had a confirmed diagnosis of WS. PPS became worsened subsequently, and a cardiac catheterization was performed at the age of 7 years. Due to severe multiple PPS, the right ventricular pressure exceeded the left ventricular pressure. At the age of 12, he had haemoptysis, which required ventilatory management. A pseudoaneurysm of the right pulmonary artery was identified and a right middle lobectomy was performed.

Methods and results

First, we performed multiplex ligation-dependent probe amplification and whole exome sequencing, considering the possibility of homozygous mutations in the region responsible for WS (7q11.23) or a larger deletion of this region in the patient. The deletion was confirmed to be a heterozygous deletion with a typical range for WS. Therefore, we hypothesized that the causative gene of severe PPS may exist separately from the region responsible for WS. After reviewing the result of the whole exome sequencing, we identified a rare nonsense variant of the “X”-gene as the disease-causing gene. The X-gene is involved in the suppression of vascular smooth muscle cell proliferation and the generation of pulmonary arteriolar dilator “Y”. The X-gene has been reported as a disease-causing gene in patients with pulmonary arterial hypertension. Based on these previous reports, we assumed that the X gene variant could be a cause of PPS; therefore, we performed functional analysis. We first introduced a mutant X-gene construct into human pulmonary arterial endothelial cells (hPAECs) and human pulmonary arterial smooth muscle cells and found that the mutant significantly reduced the production of Y compared to the wild-type X-gene. When transfected into hPAECs, the mutant X gene significantly increased cell proliferation compared to the wild-type X-gene. The hPAECs also showed reduced caspase 3/7 activity and reduced apoptosis compared to wild-type X-gene transfected cells. In the patient's own lung pathology specimens, irregular fibrous thickening of the intima of the intrapulmonary arteries was observed, which supported the results of the functional analysis.

Conclusion

Our study showed that an X-gene variant could lead to reduced Y production in the pulmonary arteries, abnormal proliferation of hPAECs, and the development of severe PPS. As Y-replenishing drugs are already in clinical use, the results may lead to the development of medical treatments for severe PPS.

Funding Acknowledgement

Type of funding sources: None.

Aortic reservoir function after arterial switch operation in elementary school-aged children

BACKGROUND

After the arterial switch procedure, decreased distensibility of the aortic root has been reported, which means impaired aortic reservoir function of the coronary circulation, but there have been no reports regarding the relationship of this issue to myocardial perfusion. Therefore, in the present study the aortic reservoir function and coronary supply-demand balance were examined in patients after undergoing the arterial switch operation (ASO) around the time of entering elementary school.

METHODS AND RESULTS

Diastolic runoff (DR), which is the percentage of diastolic blood flow to total cardiac output, was measured as the index of aortic reservoir function. The subendocardial viability ratio was investigated as the index of coronary supply - demand balance. In the patient group, the aortic root was dilated (p<0.0001) and distensibility was impaired (p<0.0001) in comparison with an age-matched control group. However, there was no difference between the 2 groups in DR or subendocardial viability ratio.

CONCLUSIONS

Coronary supply - demand balance was preserved in the pediatric ASO patients, despite the aortic root dysfunction. The preserved DR suggests that dilatation of the aorta compensates for aortic reservoir function. Because large artery dysfunction predicts future cardiovascular diseases, careful follow-up is crucial.

[Fontan completion after balloon angioplasty of multiple pulmonary artery stenosis in a child with pulmonary atresia with intact ventricular septum; report of a case]

A 5-year-old boy was referred to our institute for cardiac evaluation having been previously seen at another center. He had been diagnosed a pulmonary atresia with intact ventricular septum just after birth, and undergone Blalock-Taussig shunts. Although his central pulmonary artery pressure was high (mean pressure 26 mmHg) after bilateral Blalock-Taussig shunts, multiple peripheral pulmonary artery stenosis protected his pulmonary vascular bed from pressure load. We released the multiple pulmonary artery stenosis partly by catheter intervention and partly by surgical operation, and staged Fontan operation was completed. The surgery in combination with catheter therapies would expand the indication of Fontan-type operation, and it would contribute to the patients' postoperative prognosis.