An Adult Presentation of KIF11-Related MCLID Syndrome: Case Report and 40-Year Follow-Up

Pathogenic variants in KIF11 are linked to autosomal dominant syndromes with microcephaly, chorioretinopathy, lymphedema, and intellectual disability (MCLID), though adult presentations remain underreported. We report a 42-year-old female presenting with a de novo single-amino acid in-frame deletion in the KIF11 gene (c.1294_1296del; p.Glu432del), who exhibited severe intellectual disability, microcephaly, hypotonia, seizures, and self-injurious behavior. There was evidence of developmental delays, ophthalmologic findings, and impairments in speech and adaptive functioning in her clinical history. Trio whole exome sequencing identified a diagnostic pathogenic variant in KIF11 and a maternally inherited SCN3A variant of uncertain significance. The presentation of the case offers an unusual longitudinal perspective of over four decades, illustrating the variable expressivity and long-term outcome of KIF11 disorders. This report calls for the consideration of KIF11 variants in the differential diagnosis of syndromic developmental delay and microcephaly in adults and underlines the diagnostic as well as the prognostic importance of detailed genetic and phenotypic analysis, particularly in cases with de novo variants.