Generalized Arterial Calcification in a Recipient Twin: Discordant Fetal Hemodynamics Result in Differing Phenotypes in Monozygotic Twins with an ABCC6 Mutation

Case Report: A Novel Genetic Mutation Causes Idiopathic Infantile Arterial Calcification in Preterm Infants

Idiopathic infantile arterial calcification (IIAC), also known as generalized arterial calcification of infancy (GACI), is a heritable ectopic mineralization disorder that results in diffuse arterial calcifications and or stenosis, which are attributed to mutations in the ENPP1 gene. In this case study, we report the development of IIAC in a 2-month-old male preterm infant. The patient presented with severe hypertension and seizures, which revealed diffused calcifications and c.130C > T and c.1112A > T mutations in the ENPP1 gene. With biphosphonate, antihypertensive, and control epilepsy therapy, his blood pressure was maintained at 110–120/50–60 mmHg. Intellectual motor development retardation was anticipated in this patient. To the best of our knowledge, this is the first case in which a novel c.130C > T mutation in the ENPP1 gene has been identified, and the administration of bisphosphonates to patients with IIAC has been assessed.

Skeletal abnormalities secondary to antenatal etidronate treatment for suspected generalised arterial calcification of infancy

Background

Generalised arterial calcification of infancy (GACI) is a rare disorder characterised by the deposition of hydroxyapatite crystals within the vessel walls. It is associated with a high mortality rate. Bisphosphonates have been used with some success in the treatment of GACI. However, there is a paucity of data on the antenatal use of bisphosphonates for GACI. In this paper, we report development of the skeletal changes suggestive of hypophosphatasia (HPP) in an infant with GACI, whose mother was treated with etidronate during pregnancy.

Case report

A Caucasian infant boy had a suspected antenatal diagnosis of GACI based on the findings suggestive of calcification of the annulus of the tricuspid valve and wall of the right ventricular (RV) outflow tract and main pulmonary artery on foetal echocardiography and the genetic analysis which showed a pathogenic heterozygous mutation in ABCC6. Based on these findings, mother was started on etidronate treatment from 26 weeks of gestation. A healthy male baby was delivered at 38 weeks of gestation. Initial postnatal echocardiogram on day 1 of life was normal with good biventricular function; subtle changes suggestive of microcalcifications were detected on the CT angiography. Serum calcium, phosphate, alkaline phosphatase and renal profile were normal. Further, the serum inorganic pyrophosphate (PPi) level was significantly low. Skeletal changes suggestive of HPP were seen on the radiographs. The baby developed cardiac dysfunction on day 4 of life with evidence of ischaemic changes on electrocardiogram (ECG).Treatment with etidronate was started in view of probable evolving coronary calcifications. Despite treatment with cardiac supportive measures and bisphosphonate, he succumbed to death in the third week of life.

Discussion

We believe, this is the first report of skeletal changes suggestive of HPP, arising secondary to antenatal etidronate (first generation bisphosphonate) used for the treatment of suspected GACI due to a heterozygous ABCC6 mutation.

Bisphosphonate therapy in an infant with generalized arterial calcification with an ABCC6 mutation

Generalized arterial calcification of infancy (GACI) is a rare genetic disorder with high infantile mortality, described to be due to ENPP1, and less commonly ABCC6 mutations. Bisphosphonate treatment has been described to improve survival in ENPP1-positive GACI patients, but few studies have described bisphosphonate treatment in ABCC6-positive patients. Without therapy, patients will die before 6 months of age. Our patient is now 3 years old, former recipient twin of twin-to-twin transfusion syndrome (TTTS). Initial fetal echocardiogram at 19 weeks showed calcifications of the ascending aorta and pulmonary artery (PA). She underwent utero laser therapy, and despite resolution of the TTTS, her follow-up scans showed progressive calcification of the aorta and PA. Postnatal echocardiogram showed calcification and supravalvar stenosis of the aorta and PA. CT on day of life 6 showed calcifications in the PAs, aortic arch, and descending aorta. Quantification of valvular calcification can be difficult; in our patient, increasing outflow tract gradient on echocardiogram was used to monitor disease progression. Molecular testing revealed an ABCC6 gene mutation. She was started on weekly IV pamidronate (0.1-0.3 mg/kg/week) on day 8 of life then transitioned to oral etidronate (15-20 mg/kg/day). Given progressive supravalvar aortic and pulmonary stenosis, she underwent surgical repair with patch augmentation of the PA and ascending aorta at 4 months old. She has done well post-operatively, continuing on enteral bisphosphonate therapy with no side effects to date. Her identical twin was confirmed to have the same mutation and remains asymptomatic with no calcifications. Aggressive bisphosphonate therapy should be started as soon as possible in patients with infantile arterial calcinosis due to ABCC6 or ENPP1 mutations. Echocardiographic evaluation can be used to monitor disease progression by arterial gradients. Molecular testing is also essential to evaluate for possible co-morbidities in these patients and pregnancy management for the future.

Recipient Twin Circular Shunt Physiology Before Fetal Laser Surgery: Survival and Risks for Postnatal Right Ventricular Outflow Tract Obstruction

OBJECTIVES

To evaluate risk for congenital heart disease (CHD) in recipient twins with circular shunt physiology (CSP).

METHODS

This prospective study enrolled twin-twin transfusion syndrome (TTTS) cases from 2006 to 2015. Fetal echocardiography (FE) was performed before laser surgery when cardiac involvement was suspected. Diagnosis of recipient twin CSP required tricuspid and pulmonary regurgitation, right ventricular dysfunction, and flow reversal in the ductus arteriosus. Outcomes were assessed at 30 days after birth.

RESULTS

Of the 496 TTTS pregnancies, 20 (4%) met the criteria for CSP. Among those born alive, who had documented cardiac outcomes (n = 457), patients with CSP were more likely to have CHD, specifically right ventricular outflow tract obstruction (5 of 18 [27.8%] versus 22 of 439 [5.0%], odd ratio [OR] 7.29, 95% confidence interval [CI] 2.05-24.72, P = .0025). Of the recipient twins with preoperative FE (n = 259, 52%) who were born alive and had documented cardiac outcomes (n = 242), those with CSP were still more likely to have right ventricular outflow tract obstruction (5 of 18 [27.8%] versus 14 of 224 [6.3%], OR 5.77, CI 1.54-20.92, P = .0077). With both analyses, twins with CSP had higher Quintero stage, but similar patient characteristics and 30-day mortality compared with those without CSP. Subgroup analyses of the CSP cohort identified no differences in preoperative characteristics or FE findings predictive of CHD.

CONCLUSIONS

Recipient twins with preoperative CSP were at increased risk for postnatal right ventricular outflow tract obstruction, but appeared to have comparable survival after fetal laser surgery despite these dramatic pathophysiological prenatal findings. Preoperative FE in TTTS remains important for prediction of postnatal CHD.