Mutations in ACTL6B, coding for a subunit of the neuron-specific chromatin remodeling complex nBAF, cause early onset severe developmental and epileptic encephalopathy with brain hypomyelination and cerebellar atrophy.

Developmental and epileptic encephalopathies (DEEs) are genetically heterogenous conditions, often characterized by early onset, EEG interictal epileptiform abnormalities, polymorphous and drug-resistant seizures, and neurodevelopmental impairments. In this study, we investigated the genetic defects in two siblings who presented with severe DEE, microcephaly, spastic tetraplegia, diffuse brain hypomyelination, cerebellar atrophy, short stature, and kyphoscoliosis. Whole exome next-generation sequencing (WES) identified in both siblings a homozygous non-sense variant in the ACTL6B gene (NM_016188:c.820C>T;p.Gln274*) coding for a subunit of the neuron-specific chromatin remodeling complex nBAF. To further support these findings, a targeted ACTL6B sequencing assay was performed on a cohort of 85 unrelated DEE individuals, leading to the identification of a homozygous missense variant (NM_016188:c.1045G>A;p.Gly349Ser) in a patient. This variant did not segregate in the unaffected siblings in this family and was classified as deleterious by several prediction softwares. Interestingly, in both families, homozygous patients shared a rather homogeneous phenotype. Very few patients with ACTL6B gene variants have been sporadically reported in WES cohort studies of patients with neurodevelopmental disorders and/or congenital brain malformations. However, the limited number of patients with incomplete clinical information yet reported in the literature did not allow to establish a strong gene-disease association. Here, we provide additional genetic and clinical data on three new cases that support the pathogenic role of ACTL6B gene mutation in a syndromic form of DEE.

Copy Number Variations in Children with Tourette Syndrome: Systematic Investigation in a Clinical Setting.

Tourette syndrome (TS) is a neurodevelopmental disturbance with heterogeneous and not completely known etiology. Clinical and molecular appraisal of affected patients is mandatory for outcome amelioration. The current study aimed to understand the molecular bases underpinning TS in a vast cohort of pediatric patients with TS. Molecular analyses included array-CGH analyses. The primary goal was to define the neurobehavioral phenotype of patients with or without pathogenic copy number variations (CNVs). Moreover, we compared the CNVs with CNVs described in the literature in neuropsychiatric disorders, including TS, to describe an effective clinical and molecular characterization of patients for prognostic purposes and for correctly taking charge. Moreover, this study showed that rare deletions and duplications focusing attention on significant genes for neurodevelopment had a statistically higher occurrence in children with tics and additional comorbidities. In our cohort, we determined an incidence of potentially causative CNVs of about 12%, in line with other literature studies. Clearly, further studies are needed to delineate the genetic background of patients with tic disorders in a superior way to elucidate the complex genetic architecture of these disorders, to describe the outcome, and to identify new possible therapeutic targets.

PARK2 microdeletion in a multiplex family with autism spectrum disorder.

BACKGROUND: PARK2 (PRKN; MIM*602544) encodes Parkin protein, an ubiquitin-protein ligase required for proteasomal degradation and operating in the synaptic compartments. Copy number variations (CNVs) involving PARK2 have been associated with autism spectrum disorder (ASD). We report on a family with ASD (multiplex family) harbouring a microdeletion at chr. 6q26 causing PARK2 disruption. METHODS: CNV analyses were performed using CGH/SNP-array platforms, and the detected microdeletion was confirmed by real-time quantitative PCR. Standardized psychometric evaluation was used for neurobehavioral characterization. RESULTS: We found an intragenic ~157 kb microdeletion of the chromosomal region 6q26 causing PARK2 disruption in two male sibs with ASD and syndromic phenotype. They both had dysmorphic facial features with coarse faces, deeply set eyes with long horizontal palpebral fissures, long eyelashes and thick eyebrows, fleshy lips and mild skeletal problems. We found an intrafamilial clinical heterogeneity owing to different severity of the autism symptoms between the affected sibs: the younger one had minimally verbal autism and severe intellectual disability, whereas his older brother presented high-functioning autism and preserved speech. Parental analysis and real-time PCR using a PRKN fragment mapping within the deletion demonstrated that the deletion was inherited from their father having subthreshold features of ASD consisting with broad autism phenotype. CONCLUSIONS: The study corroborates the hypothesis that PARK2 aberrations may be associated with ASD and highlights correlations between CNV affecting PARK2 and ASD in a multiplex family. We show remarkable intrafamilial variability in the severity of inherited ASD associated with PARK2 microdeletion.

Trait - driven analysis of the 2p15p16.1 microdeletion syndrome suggests a complex pattern of interactions between candidate genes.

BACKGROUND: Individuals with the 2p15p16.1 microdeletion syndrome share a complex phenotype including neurodevelopmental delay, brain malformations, microcephaly, and autistic behavior. The analysis of the shortest region of overlap (SRO) between deletions in ~ 40 patients has led to the identification of two critical regions and four strongly candidate genes (BCL11A, REL, USP34 and XPO1). However, the delineation of their role in the occurrence of specific traits is hampered by their incomplete penetrance. OBJECTIVE: To better delineate the role of hemizygosity of specific regions in selected traits by leveraging information both from penetrant and non - penetrant deletions. METHODS: Deletions in patients that do not present a specific trait cannot contribute to delineate the SROs. We recently developed a probabilistic model that, by considering also the non - penetrant deletions, allows a more reliable assignment of peculiar traits to specific genomic segments. We apply this method adding two new patients to the published cases. RESULTS: Our results delineate an intricate pattern of genotype - phenotype correlation where BCL11A emerges as the main gene for autistic behavior while USP34 and/or XPO1 haploinsufficiency are mainly associated with microcephaly, hearing loss and IUGR. BCL11A, USP34 and XPO1 genes are broadly related with brain malformations albeit with distinct patterns of brain damage. CONCLUSIONS: The observed penetrance of deletions encompassing different SROs and that predicted when considering each single SRO as acting independently, may reflect a more complex model than the additive one. Our approach may improve the genotype/phenotype correlation and may help to identify specific pathogenic mechanisms in contiguous gene syndromes.

Biallelic intragenic duplication in ADGRB3 (BAI3) gene associated with intellectual disability, cerebellar atrophy, and behavioral disorder.

In recent years, chromosomal microarray analysis has permitted the discovery of rearrangements underlying several neurodevelopmental disorders and still represents the first diagnostic test for unexplained neurodevelopmental disabilities. Here we report a family of consanguineous parents showing psychiatric disorders and their two sons both affected by intellectual disability, ataxia, and behavioral disorder. SNP/CGH array analysis in this family demonstrated in both siblings a biallelic duplication inherited from the heterozygous parents, disrupting the ADGRB3 gene. ADGRB3, also known as BAI3, belongs to the subfamily of adhesion G protein-coupled receptors (adhesion GPCRs) that regulate many aspects of the central nervous system, including axon guidance, myelination, and synapse formation. Single nucleotide polymorphisms and copy number variants involving ADGRB3 have recently been associated with psychiatric disorders. These findings further support this association and also suggest that biallelic variants affecting the function of the ADGRB3 gene may also cause cognitive impairments and ataxia.