Isolated abnormalities in terminal regions of chromosomes 10q and 22q were formerly described in patients affected by neuropsychological impairment, abnormal facies, and heterogeneous structural abnormalities of the body. Chromosomes 10q and 22q harbor important genes that play a major role in CNS development, like DOCK1 and SHANK3, and in overall body growth, like FGFR2 and HTRA1. By using clinical, neuroradiological, neurophysiological, and genetic assessment, we studied 3 siblings affected by 2 different forms of very severe neuropsychological impairment with structural physical abnormalities, epilepsy, and body overgrowth. The genetic analysis revealed 2 different unbalanced translocations t(10;22)(q26.13;q13.32) of genetic material between the long arms of chromosomes 10 and 22, deriving from a maternal balanced translocation. Consequences of the unbalanced translocation were the simultaneous partial monosomy of 10q26.13 to 10qter and partial trisomy of 22q13.32 to 22qter in 2 patients and the simultaneous trisomy distal q10 and monosomy distal q22 in 1 patient, respectively. To the best of our knowledge, we here describe for the first time a causal association between an unbalanced translocation t(10;22) affecting the long arms of both chromosomes 10 and 22 and a very severe neurodevelopmental delay in 3 siblings.

BackgroundPatients carrying pathogenic variants inGNAO1often present with early-onset central hypotonia and global developmental delay, with or without epilepsy. As the disorder progresses, a complex hypertonic and hyperkinetic movement disorder is a common phenotype. A genotype–phenotype correlation has not yet been described and there are no evidence-based therapeutic recommendations.MethodsTo improve understanding of the clinical course and pathophysiology of this ultra-rare disorder, we built up a registry forGNAO1patients in Germany. In this retrospective, multicentre cohort study, we collected detailed clinical data, treatment effects and genetic data for 25 affected patients.ResultsThe main clinical features were symptom onset within the first months of life, with central hypotonia or seizures. Within the first year of life, nearly all patients developed a movement disorder comprising dystonia (84%) and choreoathetosis (52%). Twelve (48%) patients suffered life-threatening hyperkinetic crises. Fifteen (60%) patients had epilepsy with poor treatment response. Two patients showed an atypical phenotype and seven novel pathogenic variants inGNAO1were identified. Nine (38%) patients were treated with bilateral deep brain stimulation of the globus pallidus internus. Deep brain stimulation reduced hyperkinetic symptoms and prevented further hyperkinetic crises. The in silico prediction programmes did not predict the phenotype by the genotype.ConclusionThe broad clinical spectrum and genetic findings expand the phenotypical spectrum ofGNAO1-associated disorder and therefore disprove the assumption that there are only two main phenotypes. No specific overall genotype–phenotype correlation was identified. We highlight deep brain stimulation as a useful treatment option in this disorder.

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