History
Chief Complaint: failed critical congenital heart disease screen
A Caucasian male infant is born to a 41-year-old woman at a community hospital at 37 weeks and 3 days gestation via cesarean section because of placenta previa and breech positioning. The infant is a product of in-vitro fertilization. Routine fetal echocardiogram at 30 weeks' gestation notes a possible mitral valve leaflet abnormality. The prenatal course, otherwise, is unremarkable. Maternal history is significant for hypothyroidism, requiring Synthroid. There is no known family history of congenital heart disease or other medical disorders. The infant is vigorous at birth. He requires routine resuscitation and his Apgar scores are 9 and 9 at 1 and 5 minutes, respectively. He weighs 3,235 g (41th percentile), his head circumference is 34.5 cm (45th percentile), and length is 53.3 cm (95th percentile). The rest of his physical examination findings are normal. Maternal blood type is B+, infant blood type is also B+, coombs negative. The infant is admitted to the newborn nursery and remains well-appearing throughout his hospital stay. He is hemodynamically stable with no murmur on auscultation. On day of life 2, prior to discharge, a standard critical congenital heart disease (CCHD) screening test is performed and both pre -and post-ductal saturations are notable for oxygen saturation in the mid-80% in room air. He is placed on high flow nasal cannula (HFNC) 2L, and oxygen saturations increase to > 90%, while receiving an FiO2 of 37%. He is transferred to a regional tertiary care NICU for further management.
Physical Examination
On arrival to the NICU, the infant is well-appearing; his physical examination is only significant for mild pallor. Initial vitals included a temperature of 37.7C, a blood pressure of 89/62, heart rate of 173 bpm, respiratory rate of 60, and an oxygen saturation of 94% while on 2L HFNC oxygen supplementation. HFNC is briefly discontinued and oxygen saturations decrease to 80% in room air; he is placed back on HFNC and supplemental oxygen is titrated to keep oxygen saturation > 90%.
Laboratory/Diagnostic Procedures
An arterial blood gas on HFNC 2L, FiO2 35% shows a pH of 7.49, PO2 of 145 mm Hg, PCO2 of 30 mm Hg, bicarbonate of 23 mEq/L (23 mmol/L), base deficit of 0, and a methemoglobin of 2%. Repeat methemoglobin level is 1.7%. A complete blood count is notable for anemia, with a hemoglobin of 13 g/dL, hematocrit of 37% and reticulocyte count of 6.5%. Chest radiography shows mild prominent cardio-thymic silhouette and no acute pulmonary disease. A cardiology consult is obtained and an echocardiogram reveals a patent foramen ovale and otherwise normal intracardiac anatomy and ventricular function. Additionally, an echocardiogram bubble test is performed, which rules out left superior vena cava drainage. Given the negative cardiopulmonary work-up and multiple failed attempts to wean supplemental oxygen, pediatric hematology consult is obtained on hospital day 2 (day of life 3). Blood smear (figure 1) shows polychromasia, many target cells, schistocytes, and burr cells. Haptoglobin level is 35 mg/dL (within acceptable limits) and lactate dehydrogenase is 453 U/L (elevated). These results suggest a mild hemolytic process. Further testing reveals the diagnosis.
Final Diagnosis
A hemoglobin electrophoresis cascade is sent and shows a rare low oxygen affinity hemoglobin variant known as hemoglobin Sunshine Seth. This variant results from a point mutation on the alpha chain in which histidine replaces aspartic acid at position 94 [α2(94 (G1) Asp à His)β2]. After making the diagnosis, the patient is trialed in room air, with goals of maintaining oxygen saturations > 80%. Unfortunately, the patient's saturations intermittently drop down to mid-70% in room air; he is discharged to home on low flow nasal cannula at 0.3L, which maintains his oxygen saturations > 80%. At 1 month of age, home oxygen is discontinued; he is currently 8 months old and clinically well-appearing with oxygen saturations > 80%.
Discussion
Adult hemoglobin (Hgb) is composed of a tetramer made up of α and β globin chains. Fetal Hgb is made up of α and γ globin chains and neonates have fetal Hgb for the first several months of life. There are hundreds of known variant hemoglobin; many are clinically insignificant, but others can result in hemolytic anemia, polycythemia or methemoglobinemia. Additionally, these variants can affect how oxygen binds to the hemoglobin. Hemoglobin Sunshine Seth is a rare low oxygen affinity hemoglobinopathy that was first described in 1979. Since then, only a few case reports and case series of Hgb Sunshine Seth have been described in the neonatal period. Hgb variants that result in lower oxygen affinity result in increased oxygen delivery to peripheral tissues. This increased oxygen extraction leads to secondary cyanosis, low SpO2, and normocytic anemia. Despite cyanosis and anemia, these patients are clinically well and do not require supplemental oxygen or blood transfusions. In summary, universal screening for congenital heart disease will pick incidental cases of low oxygen affinity hemoglobinopathy. After routine negative cardio-respiratory work-up in well-appearing infants, physicians should pursue hemoglobin electrophoresis to evaluate for such hemoglobinopathies. Early diagnosis of a hemoglobinopathy will prevent unnecessary tests and prolonged hospitalization.
