Purplish granules as a cytological signature of cortical developmental disorders caused by pathogenic variants in <i>WDR81</i>
Authors: Baptiste Le Calvez, Thomas Besnard, Benjamin Cogne, Stéphane Bézieau, Marie C. Béné, Claire Beneteau, Marion Eveillard
Journal: American Journal of Hematology (2024)

A girl, born to unrelated healthy Caucasian parents, presented since birth with severe epileptic encephalopathy. Her neurological development was extremely deficient. Brain magnetic resonance imaging displayed severe microencephaly with hypoplasia of the corpus callosum. During her childhood, she developed numerous infections (such as aspiration pneumonia) related to her neurological condition. At age 12, during hospitalization for recurrent pneumonia, a complete blood count (CBC) showed a classical neutrophilic leukocytosis (leukocytes 20.1 × 109/L, neutrophils 15.2 × 109/L) without associated cytopenias (hemoglobin 124 g/L, platelets 168 × 109/L). Yet, and although the CBC instrument had not indicated any alarm for neutrophils, abnormal granules were observed microscopically in neutrophils on blood smear (Image 1). The coarse and purplish granules were later shown to be toluidine-negative, myeloperoxidase-positive, and only present in the polymorphonuclear lineage. Subsequent CBCs were then systematically investigated at high magnification. Atypical granules were then always observed but seemed to increase during each infectious episode. Blood smears of other family members did not show these abnormalities. A bone marrow aspirate performed at a distance from any infectious episode revealed these abnormal granulations at all stages of neutrophil maturation (Image 2). Investigations were nonetheless performed in search of a congenital syndrome or storage disease: metabolic balance, amino acids chromatography in blood and urine, functional analyses of polymorphonuclears, karyotype, and array CGH. No anomaly was disclosed. A whole trio exome sequencing was then performed on the child and her parents after obtaining informed genetic consent. Two pathogenic variants in WDR81 gene were identified: a deletion of 15 residues leading to a frameshift in exon 3 and a nonsynonymous single nucleotide variant generating a missense in exon 9 (c.3820_3835del, p.(Pro1274Thrfs*56) and c.5453G>T, p.(Gly1818Val) respectively, for the transcript NM_001163809.2). The c.3820_3835del deletion was inherited from the father and the c.5453G>T variant from the mother. Variants were confirmed by Sanger sequencing and segregated with the expected pattern of autosomal-recessive inheritance in all available family members. Unfortunately, the patient ultimately died at age 17 from yet another infectious pneumonia. Examination of a blood smear obtained from a second unrelated patient with WDR81 variants1 displayed the same cytologic abnormalities. WDR81 variants have been linked to various developmental neurological abnormalities ranging from cerebellar ataxia, mental retardation and disequilibrium syndrome to severe congenital hydrocephalus with microlissencephaly, corpus callosum agenesis, and pontocerebellar hypoplasia.2, 3 WDR81 is a poorly characterized gene that encodes nine protein isoforms.4 The longest isoform is predicted to be a transmembrane protein, composed of an N-terminal BEACH (Beige and Chediak-Higashi) domain. BEACH domain-containing proteins (BDCP) are known for their involvement in endolysosomal trafficking.5, 6 The LYST protein, involved in Chediak-Higashi syndrome (CHS), contains the same BEACH domain.7 CHS associates partial oculocutaneous albinism and the occurrence of hemophagocytic lymphohistiocytosis. Interestingly, adult form of CHS is characterized by neurological manifestations.8 Neurobeachin (NBEA), another BDCP, has been associated with severe autism, epilepsy and neurodevelopmental disorders.9 Again, platelets from autistic patients with disrupted NBEA have been reported to show dense granules of abnormal morphology.10 The recurrent association of similar cytological abnormalities and neurological disorders in genetic pathologies involving BDCP argues in favor of the involvement of these proteins in intracellular trafficking and autophagy-related cellular mechanisms, altering both brain cortex development and membrane fusion processes. It is therefore very likely that the cytological observation reported here in this patient with biallelic WDR81 variants falls within the same pathophysiological framework. Broader cytological exploration of patients with genetic pathologies involving BDCPs could support this hypothesis. Finally, a better understanding of this association could help guide the complex etiological diagnosis of cortical developmental malformations through a simple blood smear. BLC and ME wrote the manuscript. ME performed biological analyses. TB, BC and SB performed genetic analyses. CB treated the patient. All authors critically reviewed the manuscript. The authors are grateful to Alice Kuster and Myriam Chevalier for their assistance in the management of the patient. The authors have no conflict of interest to disclose. The data that support the findings of this study are available from the corresponding author upon reasonable request.