MedGen

A generalized myoclonic-atonic seizure is a type of generalized motor seizure characterized by a myoclonic jerk followed by an atonic motor component. [from HPO]

Cerebellar dysfunction with variable cognitive and behavioral abnormalities (CECBA) is an autosomal dominant neurologic disorder with significant phenotypic heterogeneity, even within families. The disorder is most often diagnosed through genetic analysis with retrospective clinical phenotyping. Symptom onset is usually in early childhood, although later onset, even in adulthood, has been reported. Most affected individuals show global developmental delay from early childhood, particularly of motor and language skills. Many have mild intellectual disability; behavioral and psychiatric abnormalities such as autism and obsessive-compulsive disorder are also often observed. The movement disorder is prominent and may include cerebellar signs such as ataxia, tremor, dysmetria, poor coordination, and dysarthria. Other abnormal movements including spasticity, myoclonus, and dystonia have been reported, thus widening the phenotypic spectrum. Brain imaging is usually normal, but may show cerebellar atrophy or nonspecific white matter lesions. Variable dysmorphic facial features may also be present (summary by Thevenon et al., 2012; Jacobs et al., 2021; Wijnen et al., 2020). [from OMIM]

Autosomal dominant intellectual developmental disorder-60 with seizures is characterized by global developmental delay apparent in infancy, followed by onset of seizures in the first years of life. Patients have delayed walking, an ataxic gait, and moderately to severely impaired intellectual development with poor speech (summary by Helbig et al., 2019). [from OMIM]

Autosomal dominant intellectual developmental disorder-61 (MRD61) is characterized by global developmental delay apparent in infancy with mildly impaired intellectual development, expressive speech delay, and behavioral abnormalities, including autism spectrum disorder and attention deficit-hyperactivity disorder (ADHD). Most affected individuals learn to walk on time or with some mild delay. Additional features are highly variable and may include nonspecific dysmorphic features, obstipation, ocular anomalies, and poor overall growth (Snijders Blok et al., 2018). [from OMIM]

Yoon-Bellen neurodevelopmental syndrome (YOBELN) is an autosomal recessive disorder characterized mainly by global developmental delay with variably impaired intellectual development. The manifestations and severity of the phenotype are highly variable. Additional neurologic features may include hypotonia, spasticity, ataxia, hearing loss, visual problems, seizures, and nonspecific anomalies on brain imaging (summary by Yap et al., 2021). [from OMIM]