<scp> <i>VPS4A</i> </scp> mutation in syndromic congenital hemolytic anemia without obvious signs of dyserythropoiesis
Authors: Ariane Lunati, Arnaud Petit, Hélène Lapillonne, Christine Gameiro, Virginie Saillour, Catherine Garel, Diane Doummar, Leila Qebibo, Abdelrazak Aissat, Pascale Fanen, Pablo Bartolucci, Fréderic Galactéros, Benoit Funalot, Lydie Burglen, Lamisse Mansour‐Hendili
Journal: American Journal of Hematology (2021)

Very recently, two research groups described a new neurodevelopmental syndrome with hematologic impairment, caused by de novo dominant mutations in the VPS4A gene.1, 2 Seu et al. focused on three cases characterized by Congenital Dyserythropoietic Anemia (CDA) associated with a severe neurodevelopmental disorder (global developmental delay with microcephaly, retinal dystrophy and cerebellar hypoplasia; ref.2 Rodger et al. focused on the neurodevelopmental disorder whereas hematological parameters were not extensively described.1 The VPS4A protein is a vacuolar ATPase involved in reticulocyte maturation through exosome biogenesis.3 We have independently identified another patient harboring a pathogenic VPS4A mutation. This child had a neurodevelopmental disorder and severe hemolytic anemia but no overt sign of dyserythropoiesis, which suggests that the hematological phenotype of VPS4A-related anemia could be more extended and that the diagnosis should not only be considered in patients with typical CDA. The patient was a three-year-old boy, born at term following an uncomplicated pregnancy. He was the first child of healthy unrelated parents, aged 33 (father) and 25 (mother) at the time of birth. At birth, he presented with hemolytic non-immune anemia with hemoglobin (Hb) level 92 g/L. He received transfusion at birth and became transfusion dependent (Hb 65 g/L at one month of age, before the second transfusion). Membrane and enzyme red blood cells (RBC) tests were normal before transfusions. Reticulocyte counts were always remarkably high (200 G/L to 700 G/L, 500 G/L on average) suggesting high regeneration. At 9 months of age (two months after a transfusion), the Hb level was 88 g/L; MCV, 96 fL; reticulocyte count, 461 G/L; haptoglobin level, 0.3 g/L (reference range: 0.47–1.25 g/L); LDH 892 U/L (550–1100 U/L). Serum ferritin level was 241 μg/L (10–80 μg/L); transferrin level, 1.63 g/L (2.13–3.39 g/L); serum iron level, 29.4 μmol/L (12–30 μmol/L); transferrin saturation, 72% (20%–40%). The bone marrow responsiveness index (BMRI), as defined by Russo et al.,4 was very high at 495. The patient experienced a transient peripheral thrombopenia during an episode of myositis of the left arm. Blood smear evaluation was always subnormal with non-specific anisopoikilocytosis depending on time since last transfusion. Myelogram at 3 years of age showed an erythroblastic lineage hyperplasia with balanced maturation. Results were considered as subnormal with no mention of cytologic stigma of CDA. Secondarily, we reexamined the myelogram after the VPS4A mutation had been identified. We found very few signs of dyserythropoiesis, mainly on acidophilic precursors (irregular nuclear outline, basophilic stippling, presence of a few binucleated elements without any nuclear asymetria, rare macrocytic erythroblasts; Figure 1(A)). No interchromatinian bridges, multinucleated elements or giants erythroblasts were found. Perls coloration did not reveal any ring sideroblast. Regarding neurodevelopment, the patient was hypotonic at birth and had no head control at 3 months of age. At 6 months, he presented with axial hypotonia, peripheral hypertonia, no ocular pursuit and microcephaly at −2.5 SD. At the last examination (3 years of age) he had severe axial hypotonia and choreodystonic movements with facial dyskinesia. Brain MRI at 2 years of age showed cerebral atrophy, thin dysplastic corpus callosum, basal ganglia atrophy, brainstem hypoplasia, cerebellar hypoplasia and dysplasia (Figure 1(B)). There was also a marked and diffuse widening of the diploic space of frontal calvarial bones with thickening and abnormal signal intensity of the bony structures of the cranial base, indicating a very high proliferative hematopoiesis in skull bone marrow, as described in chronic hemolytic anemia or ineffective erythropoiesis.5 Electroretinogram disclosed global bilateral retinal dysfunction suggestive of Leber congenital amaurosis. Bilateral cataracts appeared at 3 years of age. Metabolic and constitutional cytogenetic analyses were normal. Thanks to the national France Genomic Medicine 2025 (FMG2025) plan, the patient and his parents underwent Whole Genome Sequencing (WGS) with trio analysis. The proband was found to harbor a de novo heterozygous mutation in the VPS4A gene: c.850 A> T (p.R284W). The same mutation had previously been found in five out of nine identified patients with VPS4A-related disorder.1, 2 Functional testing of the p.R284W variant had been performed, showing a deleterious effect of mutated VPS4A protein on endosomal trafficking, formation of centrosome, primary cilium morphology and regulation of cell cycle in patients' fibroblasts and red blood cells.1, 2 In our patient, the absence of obvious cytologic signs of CDA in bone marrow contrasts with the hematological findings in patients described by Seu et al., including one with the same mutation, which all had clear CDA.1 This discrepancy could be due in part to the fact that patients reported by Seu et al. were included through the congenital dyserythropoietic anemia registry for North America (CDAR). In our patient, the association of a very high reticulocyte level, a very high BMRI and few signs of dyserythropoiesis in bone marrow suggests that reticulocyte maturation (autophagic organelle clearance and ubiquitin proteasome-mediated proteolysis) might be the most impaired step of terminal erythropoiesis. Indeed, VPS4 is an indispensable partner of the ESCRT III complex,1, 2 which has been shown to regulate reticulocyte proteome remodeling and organelle clearance.6 In any case, the absence of specific signs of dyserythropoiesis on bone marrow in our patient does not allow classifying his anemia as classical CDA. In addition, bone marrow morphological abnormalities are not specific to CDAs and can be found in various hereditary anemias that involve erythropoietic stress.7 It is intriguing that, among the 10 currently identified patients with VPS4A mutations, six (including the present report) harbored the same c.850A>T (p.R284W) mutation. Recurrence of this de novo mutation in several patients from different families and origins may suggest a mutational "hot spot". Frequent mechanisms involved in de novo recurrent mutations include high paternal age at conception and gain-of-function mutations conferring a selective advantage in spermatogonia. A>T transversions are very rare among de novo mutations, compared to C>G transversions and to transitions, which represent the most frequent type of de novo point mutations.8 In our case, neither paternal age at conception nor selective advantage in spermatogenesis seem to be responsible for the outcome of this mutation, even if VPS4A has an important role in human acrosome genesis.9 In conclusion, we would like to emphasize the fact that the diagnosis of VPS4A-related disorder should be considered in patients with congenital hemolytic anemia associated to severe neurodevelopmental disorder, even in the absence of overt signs of dyserythropoiesis. The exact phenotypic spectrum of this disorder will be clarified as new cases are described. We thank Dr. Bouchra Badaoui for her help in the preparation of the manuscript. This work was supported in part by the French Ministry of Health and the French Ministry of Higher Education and Research (Plan France Médecine génomique 2025). The authors declare no conflict of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.