Abstract

Neonatal cyanosis can result from a multitude of acquired and inherited causes. Cyanosis resulting from fetal M-Hemoglobin variants is a rare cause of this condition. In fact, to date, only two Gγ variants causing methemoglobinemia and cyanosis in the newborn have been reported. These are Hb F-M Osaka (Gγ63 His→Tyr) and Hb F-M Fort Ripley (Gγ92 His→Tyr). We report a novel fetal M-hemoglobin presenting with neonatal cyanosis. The propositus was a 1-day old Caucasian male admitted to the hospital because of cyanotic episodes. The patient had an O2 saturation of 85% on room air and required supplemental O2 during his 10-day hospitalization. The family history was significant for a 4-year old sister having a 5-day hospitalization after delivery for cyanosis. The sister required supplemental O2 for 4–5 months to maintain a satisfactory O2 saturation. Both parents were healthy and had no recollection of neonatal cyanosis or O2 requirement. The newborn screening for hemoglobinopathies reportedly showed Hb F, A, and a variant migrating between Hb S and Hb F. Cation exchange HPLC performed at 1-month of age revealed 68.4% Hb F; 17.5% Hb A, and 14.0% Hb X, eluting between Hb F and Hb A. Reverse phase HPLC showed only βA, αa, Gγ, and Aγ chains without any detectable abnormal chains. O2 affinity showed a P50 of 24.2mmHg (control 23.4mmHg). Sequencing of the PCR amplified Gγ gene revealed heterozygosity for a CAT→CTT mutation (His→Leu) at codon 63. (GenBank Acession # AY662983). This novel variant was named Hb F-Circleville [GγE7(63)His→Leu]. The M-hemoglobins arise from mutations in the conserved proximal (F8) or distal (E7) histidine residues, which are important heme contacts. Substitution of these residues lead to methemoglobinemia and cyanosis. Fetal Hb variants causing methemoglobinemia are rare causes of neonatal cyanosis. Hb F-Circleville is only the third fetal M-Hb reported to date. The prognosis of cyanosis is excellent in these cases, as Hb F declines post natally and is replaced by normal Hb A. Supplemental O2 may be required for several months during the postnatal period as was the case with this patient. Some fetal M-Hbs have been shown to arise as de novo mutations. In our case, an older sister and the mother were both proven to carry the Gγ63 His→Leu mutation consistent with autosomal dominant inheritance.

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