A second observation of the fetal methemoglobin variant Hb F-M-Fort Ripley or alpha 2G gamma 2(92)(F8)His----Tyr

Case Report: A case report and literature review of hemoglobin variation associated with neonatal cyanosis

We will discuss a recent case of unexplained neonatal cyanosis, evaluate its origin, clinical presentation, diagnosis, and treatment, and share with you some of our clinical insights. We report a transient cyanosis in a newborn due to a mutation in the globulin gene (HBG2), as well as diagnosis and treatment. Clinically, the infant was in good overall health, and despite low oxygen saturation, the arterial oxygen partial pressure was always normal. Early respiratory support includes mechanical ventilation, nasal tube oxygen, and eventually stopping oxygen therapy. With the above treatment measures, the blood oxygen saturation of the child always fluctuated at 85%, but the arterial blood oxygen partial pressure was up to 306 mmHg. Further improvement of laboratory tests revealed elevated methemoglobin levels, reticulocytosis, mild anemia, and basically normal on chest x-ray and echocardiography. To clarify the etiology, WES testing was performed. The results showed heterozygous variation in HBG2 gene (c.190C>T. p.H64Y). There is heterozygous variation at this site in the proband father, and no variation at this site in the proband mother. Given the age of the affected infants, we hypothesized that the mutation originated in the gamma peptide chain of the head protein. The baby was discharged from the hospital 10 days after birth, with blood oxygen saturation fluctuating around 90%. The cyanosis disappeared 2 months after discharge, and the blood oxygen saturation level returned to normal.

Case report of congenital methemoglobinemia: an uncommon cause of neonatal cyanosis

Background

Methemoglobinemia can be an acquired or congenital condition. The acquired form occurs from exposure to oxidative agents. Congenital methemoglobinemia is a rare and potentially life-threatening cause of cyanosis in newborns that can be caused by either cytochrome B₅ reductase or hemoglobin variants known as Hemoglobin M.

Case presentation

A term male infant developed cyanosis and hypoxia shortly after birth after an uncomplicated pregnancy, with oxygen saturations persistently 70–80% despite 1.0 FiO2 and respiratory support of CPAP+ 6 cm H2O. Pre- and post-ductal saturations were equal and remained below 85%. Initial radiographic and echography imaging was normal. Capillary blood gas values were reassuring with normal pH and an elevated pO2. Investigations to rule out hemolysis and end-organ dysfunction were within acceptable range. Given the absence of clear cardiac or pulmonary etiology of persistent cyanosis, hematologic causes such as methemoglobinemia were explored. No family history was available at the time of transfer to our institution. Unconjugated hyperbilirubinemia > 5 mg/dL (442 μmol/L) interfered with laboratory equipment measurement, making accurate methemoglobin levels unattainable despite multiple attempts. Initial treatment with methylene blue or ascorbic acid was considered. However, upon arrival of the presumed biological father, a thorough history revealed an extensive paternal family history of neonatal cyanosis due to a rare mutation resulting in a hemoglobin M variant. Given this new information, hematology recommended supportive care as well as further testing to confirm the diagnosis of congenital methemoglobinopathy. Whole genome sequencing revealed a likely pathogenic variation in hemoglobin. The neonate was discharged home at 2 weeks of age on full oral feeds with 0.25 L/min nasal cannula as respiratory support, with close outpatient follow-up. By 5 weeks of age, he was weaned off respiratory support.

Conclusion

Congenital methemoglobinemia should be considered in the differential diagnosis for newborns with persistent hypoxemia despite normal imaging and laboratory values. Accurate quantification of methemoglobin concentrations is challenging in neonates due to the presence of other substances that absorb light at similar wavelengths, including HbF, bilirubin, and lipids.

Diagnosis of a rare fetal haemoglobinopathy in the age of next-generation sequencing

Neonatal cyanosis resulting from a fetal methaemoglobin variant is rare. Most such variants are only described in a few published case reports. We present the case of a newborn with unexplained persistent cyanosis, ultimately determined to have a γ-chain mutation causing Hb FM-Fort Ripley. This neonatal haemoglobinopathy can be challenging to diagnose, as significant oxygen desaturation may result from barely detectable levels of the mutant haemoglobin and co-oximetry studies may show a falsely normal methaemoglobin level. Our analysis of the infant's haemoglobin included high-performance liquid chromatography, cellulose acetate electrophoresis and citrate agar electrophoresis, which showed trace amounts of a suspected variant. Ultimately, the diagnosis was made through a novel application of next-generation sequencing (NGS). NGS-based diagnostic approaches are becoming increasingly available to clinicians, and our case provides a framework and evidence for the utilisation of such testing paradigms in the diagnosis of a rare cause of neonatal cyanosis.

Hemoglobin M Disease as a Cause of Cyanosis in a Newborn

Methemoglobinemia, including the inherited or congenital form, is a known but infrequent cause of neonatal cyanosis. We present the case of a newborn patient with neonatal cyanosis, who was diagnosed with F-M-Osaka methemoglobinemia, and an up-to-date literature review of the disease.

Congenital methemoglobinaemia due to Hb F-M-Fort Ripley in a preterm newborn

Methemoglobinaemia is a rare cause of cyanosis in newborns. Congenital methemoglobinaemias due to M haemoglobin or deficiency of cytochrome b5 reductase are even rarer. We present a case of congenital methemoglobinaemia presenting at birth in a preterm infant. A baby boy born at 29 weeks and 3 days of gestation had persistent central cyanosis immediately after delivery, not attributable to a respiratory or cardiac pathology. Laboratory methemoglobin levels were not diagnostic. Cytochrome b5 reductase levels were normal and a newborn screen was unable to pick up any abnormal variants of fetal haemoglobin. Genetic testing showed a γ globin gene mutation resulting in the M haemoglobin, called Hb F-M-Fort Ripley. The baby had no apparent cyanosis at a corrected gestational age of 42 weeks. Although rare, congenital methaemoglobin aemia should be considered in the differential in a preterm with central cyanosis and investigated with genetic testing for γ globin chain mutations if other laboratory tests are non-conclusive.

Transient neonatal cyanosis associated with a new Hb F variant: Hb F viseu

Neonatal cyanosis in healthy newborns can be associated either with methemoglobin due to cytochrome b5 reductase deficiency or to M-hemoglobin, a group of hemoglobin variants resulting from mutations in the globin chain genes. We report the clinical case of a neonate with cyanosis and normal cardiac and respiratory function. At birth the hematological parameters were normal; however, the methemoglobinemia was 16%. Spontaneously, the cyanosis gradually decreased and by the fifth month of age the methemoglobin level was normal. A heterozygous Gγ-globin gene (HBG2) missense mutation 87 C-A (Leu28Met) was identified. His father, with a history of transfusion in the neonatal period, is heterozygous for the same mutation. This hemoglobin variant, not previously described, was called Hb F Viseu and is the sixth Gγ-chain variant reported in association with neonatal cyanosis.

A hemoglobin variant associated with neonatal cyanosis and anemia

Globin-gene mutations are a rare but important cause of cyanosis. We identified a missense mutation in the fetal Gγ-globin gene (HBG2) in a father and daughter with transient neonatal cyanosis and anemia. This new mutation modifies the ligand-binding pocket of fetal hemoglobin by means of two mechanisms. First, the relatively large side chain of methionine decreases both the affinity of oxygen for binding to the mutant hemoglobin subunit and the rate at which it does so. Second, the mutant methionine is converted to aspartic acid post-translationally, probably through oxidative mechanisms. The presence of this polar amino acid in the heme pocket is predicted to enhance hemoglobin denaturation, causing anemia.

Unexpectedly low pulse oximetry measurements associated with variant hemoglobins: a systematic review

Pulse oximetry estimates arterial blood oxygen saturation based on light absorbance of oxy- and deoxy-hemoglobin at 660 and 940 nm wavelengths. Patients with unexpectedly low SpO₂ often undergo cardio-pulmonary testing to ascertain the cause of their hypoxemia. However, in a subset of patients, a variant hemoglobin is responsible for low SpO₂ measurements. The extent of this problem is unclear. We performed a systematic literature review for reports of low SpO₂ associated with variant hemoglobins. We also reviewed unpublished cases from an academic hemoglobin diagnostic reference laboratory. Twenty-five publications and four unpublished cases were identified, representing 45 patients with low SpO₂ and confirmed variant hemoglobin. Fifty-seven family members of patients had confirmed or suspected variant hemoglobin. Three low oxygen affinity variant hemoglobins had concordantly low SpO₂ and SaO₂. Eleven variant hemoglobins were associated with unexpectedly low SpO₂ measurements but normal SaO₂. Hemoglobin light absorbance testing was reported in three cases, all of which showed abnormal absorption spectra between 600 and 900 nm. Seven other variant hemoglobins had decreased SpO₂, with unreported or uncertain SaO₂. Twenty-one variant hemoglobins were found to be associated with low SpO₂. Most variant hemoglobins were associated with spuriously low SpO₂. Abnormal absorption spectra explain the discrepancy between SpO₂ and SaO(2) for some variants. The differential diagnosis of possible variant hemoglobin ought to be considered in asymptomatic patients found to have unexpectedly low SpO₂. The correct diagnosis will help to spare patients from unnecessary investigations and anxiety.

Neonatal cyanosis due to a novel fetal hemoglobin: Hb F-Circleville [Ggamma63(E7)His-->Leu, CAT>CTT]

Neonatal cyanosis can result from a multitude of acquired and inherited causes. Cyanosis resulting from fetal M hemoglobin (Hb) variants is very rare. Only two (G)gamma variants causing methemoglobinemia and cyanosis in the newborn have been reported to date. Here we describe a novel fetal Hb variant, Hb F-Circleville [Ggamma63(E7)His-->Leu], associated with methemoglobinemia and cyanosis in the newborn. The patient's sister also had neonatal cyanosis at birth.

Disorders of the synthesis of human fetal hemoglobin

Fetal hemoglobin (HbF), the predominant hemoglobin in the fetus, is a mixture of two molecular species (alpha(2)(G)gamma(2) and alpha(2)(A)gamma(2)) that differ only at position 136 reflecting the products of two nonallelic gamma-globin genes. At the time of birth, HbF accounts for approximately 70% of the total Hb. The (G)gamma:(A)gamma globin ratio in the HbF of normal newborn is 70:30 whereas in the trace amounts of HbF that is found in the adult it reverses to 40:60 because of a gamma- to beta-globin gene switch. Alterations of these ratios are indicative of a molecular defect at the level of the HbF synthesis. Qualitative hemoglobinopathies due to (G)gamma and (A)gamma chain structural variants, and quantitative hemoglobinopathies affecting the synthesis of HbF such as gamma-thalassemias, duplications, triplications, and even sextuplications of the gamma-globin genes, which may be detected in newborn blood lysates, have been described. Moreover, several pathological and nonpathological conditions affecting the beta-globin gene cluster, such as beta-thalassemia, sickle cell disease, deltabeta-thalassemia, and hereditary persistence of HbF syndromes, are characterized by the continued synthesis of gamma-globin chains in the adult life. Studies of these natural mutants associated with increased synthesis of HbF in adult life have provided considerable insight into the understanding of the control of globin gene expression and Hb switching.

Two new mutations in cis on (G)gamma chain of fetal hemoglobin: Hb F-Madrid [G gamma 50(D1)Ser-->Cys] and [G gamma 75(E19)Ile-->Thr]

We describe a new structural hemoglobin variant of (G)gamma with two amino acid replacements in cis found in the umbilical cord blood of a neonate in Madrid, Spain. The substitutions were identified on exon 2 of the (G)gamma globin gene, at codon 50 (T CT-->T GT) and at codon 75 (A TA-->A CA). We have named it Hb F-Madrid. The father of the propositus was the carrier of the same (G)gamma chain variant and, moreover, molecular study of alpha genes revealed the loss of an alpha gene (-alpha(3.7)/alpha alpha) both in the propositus and his mother.

Hb FM-Fort Ripley: confirmation of autosomal dominant inheritance and diagnosis by PCR and direct nucleotide sequencing

We describe a normal neonate who presented at four days of age with asymptomatic cyanosis. There was no evidence of cardiac or pulmonary abnormality and an extended family history included 13 other affected family members with asymptomatic cyanosis lasting one to three months. Polymerase chain reaction (PCR) amplification and direct nucleotide sequencing of the proband's G gamma chain gene revealed the mutation at codon 92 (CAC-->TAC) previously shown in haemoglobin FM-Fort Ripley (alpha 2 gamma G gamma 92 (F8) His-->Tyr). This is the first family with Hb FM-Fort Ripley reported so far. It demonstrates autosomal dominant inheritance of this condition and incomplete penetrance.