A novel SYNJ1 homozygous variant causing developmental and epileptic encephalopathy in an Afro‐Caribbean individual

BACKGROUND: SYNJ1 encodes Synaptojanin‐1, a dual‐function poly‐phosphoinositide phosphatase that is expressed in the brain to regulate neuronal synaptic vesicle dynamics. Biallelic SYNJ1 variants cause a spectrum of clinical manifestations, from early onset parkinsonism to developmental and epileptic encephalopathy. METHODS: Proband‐only exome sequencing was used to identify a homozygous SYNJ1 pathogenic variant in an individual with epileptic encephalopathy. Sanger sequencing was used to confirm the variant. RESULTS: We present an Afro‐Caribbean female who developed uncontrollable seizures shortly after birth, accompanied by developmental delay and severe generalized dystonia. She had homozygosity for a novel c.242‐2A > G variant in SYNJ1 with both parents being heterozygous carriers. An older sister was reported to have had a similar presentation but was not examined. Both siblings died at an approximate age of 16 years. CONCLUSIONS: We report a novel pathogenic variant in SYNJ1 present in homozygosity leading to developmental and epileptic encephalopathy. Currently, there are only 4 reports describing 10 individuals with SYNJ1‐related developmental and epileptic encephalopathy. This case expands the clinical knowledge and the allelic heterogeneity associated with SYNJ1 variants.