Severe neonatal jaundice due to a de novo glucose‐6‐phosphate dehydrogenase deficient mutation

Sir, Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human enzyme deficiency worldwide and has long been associated with reduced-efficiency erythrocytes [1]. Acute haemolysis induced by exposure to oxidative stress, related to infection, drugs or fava bean ingestion, is the most frequent clinical presentation; however, G6PD class 1 deficiency causes chronic haemolysis and could be a major contributor to neonatal hyperbilirubinemia [2]. To date, various different mutations in G6PD gene have been identified, most frequently on exon 10 and a minor cluster on exons 6, 7 and 8 [3]. Most of these mutations lead to amino acid replacements close to the dimer interface within the ‘structural’ NADP+-binding site, suggesting that the integrity of these regions is very important for the formation of stable dimers [4, 5]. The present letter reports a case of a newborn infant with severe class 1 G6PD deficiency associated with a de novo G6PD mutation. The patient was a male, born at 39 weeks by Caesarean section (second pregnancy). The parents of Spanish origin were nonconsanguineous, and no family members had a history of anaemia or jaundice. A few hours after birth, he developed clinical respiratory distress accompanied by skin pallor, jaundice, hepatomegaly and splenomegaly. Blood tests showed a haemoglobin (Hb) level of 90 g/L, total bilirubin level of 11.2 mg/dL (normal 1–12 mg/dL) and direct bilirubin level of 4.4 mg/dL. A peripheral blood smear did not reveal spherocytes. Phototherapy and an exchange transfusion were needed at 15 h of life to treat severe hyperbilirubinemia (17.4 mg/dL). The patient was discharged after 21 days, with a probable diagnosis of ABO incompatibility (proband blood group A RhD+, mother: O RhD+, slightly positive direct antiglobulin test). At 6 weeks of life, follow-up blood tests showed persistence of regenerative anaemia with Hb 72 g/L, reticulocyte count 328 9 10/lL, total bilirubin 0.5 mg/dL, lactate dehydrogenase 213 U/L (5–510), haptoglobin 58 mg/dL (50–200) and no spherocytes, and signs of oxidative stress or other pathological findings were observed in the blood smear. Analysis of enzyme activity showed reduced G6PD activity (145 mU/10 red blood cells; normal value: 221–570 mU/10 red blood cells). The direct antiglobulin test was negative, neurological status was normal and physical examination did not reveal splenomegaly. Subsequently, baseline Hb levels stabilized at 90 to 120 g/L and reticulocytes at 180 to 320 9 10/lL, while bilirubin levels normalized without transfusions, also a second assay of G6PD activity confirmed severe deficiency (30 mU/10 red blood cells). At 9 months old, the patient was admitted to hospital with haemolytic anaemia (Hb 55 g/L, reticulocytes 196 9 10/lL, lactate dehydrogenase 2250 U/L, total bilirubin 1.2 mg/dL) secondary to an infectious process and received a single-unit red blood cell transfusion. Genetic studies were performed after informed consent. Genomic DNA was extracted from peripheral blood of the proband and mother, using standard methods. The G6PD gene was amplified by polymerase chain reaction from exon 2 to 13, amplified in genomic DNA of the proband and mother, and analysed by direct sequencing with the dideoxy chain termination reaction using an ABI PRISM 3130 Genetic Analyser and BigDye Terminator v1.1 Cycle Sequencing Kit (Applied Biosystems, Foster City, CA, USA). The sequencing analysis of the G6PD gene on the proband revealed a previously described cytosine-to-thymine transition at position c.827 on exon 8, resulting in an amino acid change (proline to leucine) at the residue 276 (c.827C>T; p.Pro276Leu). This mutation was absent in genomic DNA from the proband’s mother. The degree of mosaicism for the identified mutation was assessed by bidirectional sequencing in independent DNA samples from the proband obtained from peripheral blood containing EDTA buccal cells and hair. Sequencing confirmed the results previously obtained with the peripheral blood DNA and did not reveal a double peak at the mutation site (Figure 1). Human leukocyte antigen – short tandem repeat markers were analysed in the proband and his mother using Luminex (Gen-Probe