Kaptin-Actin Binding Protein (KPTN)-Related Disorder: A Case Report of Two Siblings Harboring a Novel KPTN Mutation

Kaptin-actin binding protein (KPTN)-related disorder is a rare autosomal recessive neurogenetic syndrome resulting from mutations in the KPTN gene, encoding the actin-binding protein kaptin. Symptoms experienced by individuals with KPTN-related disorder vary, but common features include intellectual disability, developmental delay, psychiatric manifestations, neonatal hypotonia, macrocephaly, and seizures. This case report describes two siblings from the United States affected by KPTN-related disorder, patient B (a 32-year-old woman) and patient M (a 30-year-old man). Both patients B and M have intellectual impairment, have had developmental delay/regression, and exhibit a range of neuropsychiatric symptoms. Additionally, both patients B and M experience seizures, with patient B primarily having absence seizures, and patient M having frequent myoclonic seizures. Interestingly, both patients discussed here maternally inherited a novel KPTN mutation, not previously identified in other individuals with KPTN-related disorder, to our knowledge. Of particular interest in this case is that several members of the maternal family were observed to have myoclonic seizures, raising the intriguing possibility that this newly identified KPTN mutation may lead to mild symptoms even in heterozygous carriers of this mutation. Furthermore, we discuss the recent diagnosis of both patients with sleep apnea, a feature not previously identified in other patients with KPTN-related disorder.