Erythroid transcription factor EKLF/KLF1 mutation causing congenital dyserythropoietic anemia type IV in a patient of Taiwanese origin: Review of all reported cases and development of a clinical diagnostic paradigm

Abstract

KLF1 is an erythroid specific transcription factor that is involved in erythroid lineage commitment, globin switching and terminal red blood cell maturation. Various mutations of KLF1 have been identified in humans, which has led to both benign and pathological phenotypes. The E325K mutation, within the second zinc finger of the KLF1 gene, has been shown to cause a new form of congenital dyserythropoietic anemia (CDA) now labeled as CDA type IV. We report the fourth documented case of this mutation, and propose a clinical diagnostic model to better identify this disease in other patients. Our patient is a Taiwanese child who presented to us at 8 years of age with severe hemolytic anemia, splenomegaly, elevated fetal hemoglobin (HbF), iron overload, and dyserythropoiesis in the bone marrow. KLF1 sequence analysis revealed a G-to-A transition in one allele of exon 3, which resulted in the substitution of a glutamate 325 by a lysine. Flow cytometry analysis revealed decreased protein expression of CD44 on the red blood cells, and decreased red blood cell deformability as measured using an ektacytometer. Blood typing revealed his red blood cells to be Co(a−b−), In(b−), LW(ab−) and Lu(b+), even though DNA testing predicted he would be Co(a+b−) and LW(a+b−ab+). This newly discovered CDA combines features of a hemoglobinopathy, RBC membrane defect and hereditary persistence of HbF (HPFH) which is not seen in previous types of CDA. Increased awareness of this phenotype may improve more prompt and accurate diagnosis of these patients.

Neomorphic effects of the neonatal anemia (Nan-Eklf) mutation contribute to deficits throughout development

“…In the present case, the most direct connection is with CDA type IV (Iolascon et al, 2012), which is caused by a mutation in human KLF1 at the same amino acid (Arnaud et al, 2010;Jaffray et al, 2013;Singleton et al, 2011). The change is non-conservative (E to K), so although not all characteristics of the Nan mouse may apply, individuals with CDA exhibit altered globin switching and membrane deficits that are highly reminiscent of the present model (discussed by Siatecka et al, 2010b).…”

“…However, some mutations lead to anemias (Arnaud et al, 2010;Huang et al, 2015;Jaffray et al, 2013;Singleton et al, 2011;Viprakasit et al, 2014; reviewed by Perkins et al, 2016). The human KLF1 mutation (E325K) in congenital dyserythropoietic anemia (CDA) (Arnaud et al, 2010;Jaffray et al, 2013;Singleton et al, 2011) is at the same amino acid as that seen in the mouse Nan mutant (Heruth et al, 2010;Siatecka et al, 2010b), albeit a different substitution. Nan is inherited in a semi-dominant fashion: homozygotes die in utero at E10-11, while heterozygous Nan/+ mice exhibit lifelong severe anemia that is characterized by reticulocytosis, splenomegaly, altered globin expression and cell membrane defects (Lyon, 1983;Siatecka et al, 2010b;White et al, 2009).…”

Extrinsic and intrinsic control by EKLF (KLF1) within a specialized erythroid niche

“…Abnormal numbers of nucleated red cells are observed in EKLFnull embryos (Perkins et al, 1995), and are also a characteristic of human CDA type IV patients who contain a mutation in one allele of KLF1 (Arnaud et al, 2010;Jaffray et al, 2013). This variant is altered within the second zinc finger (E325K), changing its cognate binding specificity and probably converting it to an interfering protein (Singleton et al, 2011).…”

Compound heterozygosity for KLF1 mutations is associated with microcytic hypochromic anemia and increased fetal hemoglobin

“…CDA IV combines features of hemoglobinopathy, red blood cell (RBC) membrane defects, and hereditary persistence of fetal hemoglobin (HPFH), which are not seen in the other types of CDA. 11,12 However, various mutations in human KLF1 have been described that are associated with benign phenotypes. Compound heterozygotes for KLF1 mutations are associated with both benign and disease phenotypes.…”