PP01.7 – 2726: A novel description of a homozygous partial deletion of RBFOX1 gene causing epileptic encephalopathy, severe intellectual disability and progressive post-natal microcephaly

Objective Partial deletions of the gene encoding the neuronal splicing regulator RBFOX1 have been reported in a range of neurodevelopmental diseases, including idiopathic generalized epilepsy, Rolandic epilepsy (RE), Autosomal dominant lateral temporal epilepsy (ADLTE) or idiopathic generalized epilepsy (IGE). Patients often exhibit severe co-morbid neuro-developmental disorders such as intellectual disability (ID) and Autism spectrum disorders (ASD) or microcephaly. Heterozygous RBFOX1 knockout mouse models demonstrate deregulated splicing, disrupting genes involved in synaptic transmission and membrane excitability leading to increased susceptibility for seizure events. All patients reported so far have a hemizygous deletion/mutation and the transmitting parents in most cases were asymptomatic. We report a female toddler, that first presented with adversive seizures at four months of age, progressing to intractable epilepsy. EEG demonstrated generalized spike & wave activity. Currently at the age of thirty months she has profound ID and progressive post-natal microcephaly. Extensive diagnostic workup was uninformative – including whole exome sequencing (WES) for known epilepsy mutations. Brain MRI demonstrated non-specific findings. Her parents are first cousins of Arab origin. Ten family members are noted for epilepsy, intellectual disability of different severities and autism, however none has the same severe presentation as the patient. Methods and results Chromosomal micro-array analysis (CMA) revealed a 426 KB homozygous deletion in chromosome 16p13.3 at the 5' UTR end of the RBFOX1 gene. The asymptomatic parents are heterozygous for the deletion. Conclusion This is the first case of a homozygous partial deletion of the RBFOX1 gene in a toddler suffering from epileptic encephalopathy with profound ID and progressive postnatal microcephaly detected by CMA. Our case strengthens the association of partial RBFOX1 deletions in neurodevelopmental diseases and extends the RBFOX1-related phenotypic spectrum. Partial deletions of the gene encoding the neuronal splicing regulator RBFOX1 have been reported in a range of neurodevelopmental diseases, including idiopathic generalized epilepsy, Rolandic epilepsy (RE), Autosomal dominant lateral temporal epilepsy (ADLTE) or idiopathic generalized epilepsy (IGE). Patients often exhibit severe co-morbid neuro-developmental disorders such as intellectual disability (ID) and Autism spectrum disorders (ASD) or microcephaly. Heterozygous RBFOX1 knockout mouse models demonstrate deregulated splicing, disrupting genes involved in synaptic transmission and membrane excitability leading to increased susceptibility for seizure events. All patients reported so far have a hemizygous deletion/mutation and the transmitting parents in most cases were asymptomatic. We report a female toddler, that first presented with adversive seizures at four months of age, progressing to intractable epilepsy. EEG demonstrated generalized spike & wave activity. Currently at the age of thirty months she has profound ID and progressive post-natal microcephaly. Extensive diagnostic workup was uninformative – including whole exome sequencing (WES) for known epilepsy mutations. Brain MRI demonstrated non-specific findings. Her parents are first cousins of Arab origin. Ten family members are noted for epilepsy, intellectual disability of different severities and autism, however none has the same severe presentation as the patient. Chromosomal micro-array analysis (CMA) revealed a 426 KB homozygous deletion in chromosome 16p13.3 at the 5' UTR end of the RBFOX1 gene. The asymptomatic parents are heterozygous for the deletion. This is the first case of a homozygous partial deletion of the RBFOX1 gene in a toddler suffering from epileptic encephalopathy with profound ID and progressive postnatal microcephaly detected by CMA. Our case strengthens the association of partial RBFOX1 deletions in neurodevelopmental diseases and extends the RBFOX1-related phenotypic spectrum.