ANKLE2-related microcephaly: A variable microcephaly syndrome resembling Zika infection.

OBJECTIVE: This study delineates the clinical and molecular spectrum of ANKLE2-related microcephaly (MIC), as well as highlights shared pathological mechanisms between ANKLE2 and the Zika virus. METHODS: We identified 12 individuals with MIC and variants in ANKLE2 with a broad range of features. Probands underwent thorough phenotypic evaluations, developmental assessments, and anthropometric measurements. Brain imaging studies were systematically reviewed for developmental abnormalities. We functionally interrogated a subset of identified ANKLE2 variants in Drosophila melanogaster. RESULTS: All individuals had MIC (z-score ≤ -3), including nine with congenital MIC. We identified a broad range of brain abnormalities including simplified cortical gyral pattern, full or partial callosal agenesis, increased extra-axial spaces, hypomyelination, cerebellar vermis hypoplasia, and enlarged cisterna magna. All probands had developmental delays in at least one domain, with speech and language delays being the most common. Six probands had skin findings characteristic of ANKLE2 including hyper- and hypopigmented macules. Only one individual had scalp rugae. Functional characterization in Drosophila recapitulated the human MIC phenotype. Of the four variants tested, p.Val229Gly, p.Arg236*, and p.Arg536Cys acted as partial-loss-of-function variants, whereas the c.1421-1G>C splicing variant demonstrated a strong loss-of-function effect. INTERPRETATION: Deleterious variants in the ANKLE2 gene cause a unique MIC syndrome characterized by congenital or postnatal MIC, a broad range of structural brain abnormalities, and skin pigmentary changes. Thorough functional characterization has identified shared pathogenic mechanisms between ANKLE2-related MIC and congenital Zika virus infection. This study further highlights the importance of a thorough diagnostic evaluation including molecular diagnostic testing in individuals with MIC.

Mutations of KIF5C cause a neurodevelopmental disorder of infantile-onset epilepsy, absent language, and distinctive malformations of cortical development.

The clinical diagnosis of malformations of cortical development (MCDs) is often challenging due to the complexity of the brain malformation by neuroimaging, the rarity of individual malformation syndromes, and the rapidly evolving genetic landscape of these disorders facilitated with the use of Next Generation Sequencing (NGS) methods. While the clinical and molecular diagnosis of severe cortical malformations, such as classic lissencephaly, is often straightforward, the diagnosis of more subtle and complex types of cortical malformations, such as pachygyria and polymicrogyria (PMG), can be more challenging due to limited knowledge regarding their genetic etiologies. Here, we report two individuals with the same de novo KIF5C mutation who present with subtle MCDs, early onset epilepsy and significant neurodevelopmental and behavioral issues including absent language. Our data, combined with the limited literature on KIF5C mutations, to date, support that KIF5C mutations are associated with a neurodevelopmental disorder characterized by infantile onset epilepsy, and subtle but recognizable types of brain malformations. We also show that the spectrum of KIF5C mutations is narrow, as five out of the six identified individuals have mutations affecting amino acid Glu237. Therefore, the identification of the clinical and neuroimaging features of this disorder may strongly facilitate rapid and efficient molecular diagnosis.