CUX1-related neurodevelopmental disorder: deep insights into phenotype-genotype spectrum and underlying pathology.

Heterozygous, pathogenic CUX1 variants are associated with global developmental delay or intellectual disability. This study delineates the clinical presentation in an extended cohort and investigates the molecular mechanism underlying the disorder in a Cux1+/- mouse model. Through international collaboration, we assembled the phenotypic and molecular information for 34 individuals (23 unpublished individuals). We analyze brain CUX1 expression and susceptibility to epilepsy in Cux1+/- mice. We describe 34 individuals, from which 30 were unrelated, with 26 different null and four missense variants. The leading symptoms were mild to moderate delayed speech and motor development and borderline to moderate intellectual disability. Additional symptoms were muscular hypotonia, seizures, joint laxity, and abnormalities of the forehead. In Cux1+/- mice, we found delayed growth, histologically normal brains, and increased susceptibility to seizures. In Cux1+/- brains, the expression of Cux1 transcripts was half of WT animals. Expression of CUX1 proteins was reduced, although in early postnatal animals significantly more than in adults. In summary, disease-causing CUX1 variants result in a non-syndromic phenotype of developmental delay and intellectual disability. In some individuals, this phenotype ameliorates with age, resulting in a clinical catch-up and normal IQ in adulthood. The post-transcriptional balance of CUX1 expression in the heterozygous brain at late developmental stages appears important for this favorable clinical course.

2q24 deletions: further characterization of clinical findings and their relation to the SCN cluster.

As the resolution of molecular cytogenetic methods continues to improve, it has become increasingly possible to refine genotype-phenotype correlations based upon gene involvement. We report three new patients with nonrecurrent deletions involving subbands of 2q24. These patients were referred for evaluation of developmental delay, but were found to have unique, nonoverlapping clinical features. Patient 1 presented with infantile seizures, microcephaly, and brain anomalies, along with facial dysmorphism, growth retardation, neuromuscular scoliosis, and later with developmental regression. Array comparative genomic hybridization (aCGH) detected an 8 Mb interstitial deletion encompassing the neuronal sodium channel (SCN) gene cluster. Patient 2 presented with growth retardation, congenital heart defect, and hypotonia. Patient 3 presented with developmental delay and behavioral problems. Patients 2 and 3 had no history of seizures, microcephaly, or brain anomalies and were found to have deletions of 2q24, ∼8 Mb and <500 kb respectively, centromeric to and outside the SCN cluster. It has been demonstrated that mutations and copy number variants (CNVs) affecting the SCN gene cluster result in severe, early-onset seizures. It is however, less clear whether haploinsufficiency of regions outside the SCN cluster may result in phenotypically recognizable and clinically significant features. We discuss additional dosage sensitive genes that may exist outside the SCN cluster. Our and published data indicate that 2q24 deletions not involving the SCN cluster are associated with fewer neurobehavioral problems, but may predispose to congenital malformations.

PURA-Related Developmental and Epileptic Encephalopathy: Phenotypic and Genotypic Spectrum.

BACKGROUND AND OBJECTIVES: Purine-rich element-binding protein A (PURA) gene encodes Pur-α, a conserved protein essential for normal postnatal brain development. Recently, a PURA syndrome characterized by intellectual disability, hypotonia, epilepsy, and dysmorphic features was suggested. The aim of this study was to define and expand the phenotypic spectrum of PURA syndrome by collecting data, including EEG, from a large cohort of affected patients. METHODS: Data on unpublished and published cases were collected through the PURA Syndrome Foundation and the literature. Data on clinical, genetic, neuroimaging, and neurophysiologic features were obtained. RESULTS: A cohort of 142 patients was included. Characteristics of the PURA syndrome included neonatal hypotonia, feeding difficulties, and respiratory distress. Sixty percent of the patients developed epilepsy with myoclonic, generalized tonic-clonic, focal seizures, and/or epileptic spasms. EEG showed generalized, multifocal, or focal epileptic abnormalities. Lennox-Gastaut was the most common epilepsy syndrome. Drug refractoriness was common: 33.3% achieved seizure freedom. We found 97 pathogenic variants in PURA without any clear genotype-phenotype associations. DISCUSSION: The PURA syndrome presents with a developmental and epileptic encephalopathy with characteristics recognizable from neonatal age, which should prompt genetic screening. Sixty percent have drug-resistant epilepsy with focal or generalized seizures. We collected more than 90 pathogenic variants without observing overt genotype-phenotype associations.