When Extra Gene Speaks: Genotype-Phenotype Correlation in Partial Duplication of Chromosome 13, A Case Report

Partial duplication of chromosome 13q is a rare chromosomal disorder associated with congenital anomalies, neurodevelopmental impairment, and refractory epilepsy. We report a 6.5-year-old male who presented with dysmorphism, seizures and developmental delay. Child was born at term gestation with low birth weight to non-consanguineous parents, with three prior maternal spontaneous abortions. Brief upper-limb flexion episodes began on day 3 of life but were evaluated only at 7 weeks of age during an admission for lower respiratory tract infection, when valproate and clobazam were initiated. Despite normal early neuroimaging, global developmental delay persisted. Over the last 6-7 months, he developed increased seizure frequency and loss of milestones. Examination showed microcephaly with trigonocephaly, right irido-fungal coloboma, bilateral post-axial polydactyly, bilateral undescended testes with right inguinal hernia, and mild right-sided sensorineural hearing loss. Metabolic workup was normal. Repeat MRI brain remained unremarkable, while EEG showed generalized epileptiform discharges with sleep activation (SWI >60%). Abdominal ultrasonography and echocardiography were normal. Whole-exome sequencing revealed a pathogenic duplication of chromosome 13q13.3-q34; parental karyotypes were normal, confirming a de novo event. Seizures improved with zonisamide and clobazam, and the child was started on physiotherapy while awaiting hernia repair. This case highlights the need for early genetic evaluation in children with syndromic features, refractory epilepsy, and developmental delay to enable accurate diagnosis and counselling.