Brain Abnormalities in Patients with Germline Variants in H3F3: Novel Imaging Findings and Neurologic Symptoms Beyond Somatic Variants and Brain Tumors.

BACKGROUND AND PURPOSE: Pathogenic somatic variants affecting the genes Histone 3 Family 3A and 3B (H3F3) are extensively linked to the process of oncogenesis, in particular related to central nervous system tumors in children. Recently, H3F3 germline missense variants were described as the cause of a novel pediatric neurodevelopmental disorder. We aimed to investigate patterns of brain MR imaging of individuals carrying H3F3 germline variants. MATERIALS AND METHODS: In this retrospective study, we included individuals with proved H3F3 causative genetic variants and available brain MR imaging scans. Clinical and demographic data were retrieved from available medical records. Molecular genetic testing results were classified using the American College of Medical Genetics criteria for variant curation. Brain MR imaging abnormalities were analyzed according to their location, signal intensity, and associated clinical symptoms. Numeric variables were described according to their distribution, with median and interquartile range. RESULTS: Eighteen individuals (10 males, 56%) with H3F3 germline variants were included. Thirteen of 18 individuals (72%) presented with a small posterior fossa. Six individuals (33%) presented with reduced size and an internal rotational appearance of the heads of the caudate nuclei along with an enlarged and squared appearance of the frontal horns of the lateral ventricles. Five individuals (28%) presented with dysgenesis of the splenium of the corpus callosum. Cortical developmental abnormalities were noted in 8 individuals (44%), with dysgyria and hypoplastic temporal poles being the most frequent presentation. CONCLUSIONS: Imaging phenotypes in germline H3F3-affected individuals are related to brain features, including a small posterior fossa as well as dysgenesis of the corpus callosum, cortical developmental abnormalities, and deformity of lateral ventricles.

Calbindin D28K expression in relation to granule cell dispersion, mossy fibre sprouting and memory impairment in hippocampal sclerosis: a surgical and post mortem series.

Reorganisation of the dentate gyrus, including granule cell dispersion (GCD) and mossy fibre sprouting, typically accompany hippocampal sclerosis (HS) in temporal lobe epilepsy. Calbindin (CB) expression in granule cells increases during infancy, influences granule cell excitability, vulnerability to excitotoxicity in addition to important physiological functions in memory. Our aim was to study CB patterns in relation to dentate gyrus re-organisation, epilepsy history and memory function. Forty-five surgical cases and 11 post mortems were examined from patients with drug-resistant epilepsy in addition to three post mortem controls. In the surgical cases, CB expression, and the degree of GCD and mossy fibre sprouting were measured. In post mortem cases, CB expression was assessed in relation to the pattern of HS along the rostral-caudal axis of the hippocampus, and compared to PM controls. Three patterns were identified. In Group 1 (40%), the most dispersed granule cells were CB-positive and basal cells negative imitating developmental patterns. In Group 2 (47%), normal CB expression was retained and in Group 3 (13%), CB was predominantly lost in granule cells. These patterns correlated with GCD, the presence of mossy fibre sprouting and the pattern of HS. Group 1 was associated with early onset of seizures but not independently predictive of outcome. In post mortem cases, altered CB expression lateralised to the side of HS and persisted despite seizure remission in some patients. No significant correlation between CB expression and memory function was identified. CB expression patterns in HS may indicate developmental dysmaturation and are associated with the extent of GCD and mossy fibre sprouting in HS. The functional significance of CB loss, in terms of epileptogenesis and effects on memory, remain uncertain.