Abstract
Extreme microcephaly and rhombencephalosynapsis represent unusual pathological conditions, each of which occurs in isolation or in association with various other cerebral and or extracerebral anomalies. Unlike microcephaly for which several disease-causing genes have been identified with different modes of inheritance, the molecular bases of rhombencephalosynapsis remain unknown and rhombencephalosynapsis presents mainly as a sporadic condition consistent with de novo dominant variations. We report for the first time the association of extreme microcephaly with almost no sulcation and rhombencephalosynapsis in a fœtus for which comparative patient-parent exome sequencing strategy revealed a heterozygous de novo missense variant in the ADGRL2 gene. ADGRL2 encodes latrophilin 2, an adhesion G-protein-coupled receptor whose exogenous ligand is α-latrotoxin. Adgrl2 immunohistochemistry and in situ hybridization revealed expression in the telencephalon, mesencephalon and rhombencephalon of mouse and chicken embryos. In human brain embryos and fœtuses, Adgrl2 immunoreactivity was observed in the hemispheric and cerebellar germinal zones, the cortical plate, basal ganglia, pons and cerebellar cortex. Microfluorimetry experiments evaluating intracellular calcium release in response to α-latrotoxin binding showed significantly reduced cytosolic calcium release in the fœtus amniocytes vs amniocytes from age-matched control fœtuses and in HeLa cells transfected with mutant ADGRL2 cDNA vs wild-type construct. Embryonic lethality was also observed in constitutive Adgrl2−/− mice. In Adgrl2+/− mice, MRI studies revealed microcephaly and vermis hypoplasia. Cell adhesion and wound healing assays demonstrated that the variation increased cell adhesion properties and reduced cell motility. Furthermore, HeLa cells overexpressing mutant ADGRL2 displayed a highly developed cytoplasmic F-actin network related to cytoskeletal dynamic modulation. ADGRL2 is the first gene identified as being responsible for extreme microcephaly with rhombencephalosynapsis. Increased cell adhesion, reduced cell motility and cytoskeletal dynamic alterations induced by the variant therefore represent a new mechanism responsible for microcephaly.
Highlights
Extreme microcephaly and rhombencephalosynapsis represent unusual pathological conditions, each of which occurs in isolation or in association with various other cerebral and or extracerebral anomalies
Using comparative patient-parents exome sequencing strategy, a powerful method to detect de novo pathogenic variants involved in human Mendelian genetic diseases [52, 53], we identified the first molecular basis of this association of extreme microcephaly with severely reduced sulcation with RES in a fœtus, a deleterious variant in the ADGRL2 gene, which encodes an adhesion G-ProteinCoupled Receptor (GPCR)
In conclusion, we have identified an ADGRL2 variation very likely responsible for severe microcephaly with almost no sulcation highlighting a new mechanism for the two associated malformations related to excessive adhesion of neuron progenitors within the germinal zones at least mediated by reduction of Ca2+ transients
Summary
Extreme microcephaly and rhombencephalosynapsis represent unusual pathological conditions, each of which occurs in isolation or in association with various other cerebral and or extracerebral anomalies. Unlike microcephaly for which several disease-causing genes have been identified with different modes of inheritance, the molecular bases of rhombencephalosynapsis remain unknown and rhombencephalosynapsis presents mainly as a sporadic condition consistent with de novo dominant variations. We report for the first time the association of extreme microcephaly with almost no sulcation and rhombencephalosynapsis in a fœtus for which comparative patientparent exome sequencing strategy revealed a heterozygous de novo missense variant in the ADGRL2 gene. Using comparative patient-parents exome sequencing strategy, a powerful method to detect de novo pathogenic variants involved in human Mendelian genetic diseases [52, 53], we identified the first molecular basis of this association of extreme microcephaly with severely reduced sulcation with RES in a fœtus, a deleterious variant in the ADGRL2 gene, which encodes an adhesion G-ProteinCoupled Receptor (GPCR). Mechanistic and functional characterization of the variant provides compelling evidence that this deleterious variant causes early human developmental defects involving both supratentorial and infratentorial structures
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have