Prenatal cerebral imaging features of a new syndromic entity related to KIAA1109 pathogenic variants mimicking tubulinopathy

Prenatal phenotyping of fetal tubulinopathies: A multicenter retrospective case series

OBJECTIVE

Tubulinopathies refer to conditions caused by genetic variants in isotypes of tubulin resulting in defective neuronal migration. Historically, diagnosis was primarily via postnatal imaging. Our objective was to establish the prenatal phenotype/genotype correlations of tubulinopathies identified by fetal imaging.

METHODS

A large, multicenter retrospective case series was performed across nine institutions in the Fetal Sequencing Consortium. Demographics, fetal imaging reports, genetic screening and diagnostic testing results, delivery reports, and neonatal imaging reports were extracted for pregnancies with a confirmed molecular diagnosis of a tubulinopathy.

RESULTS

Nineteen pregnancies with a fetal tubulinopathy were identified. The most common prenatal imaging findings were cerebral ventriculomegaly (15/19), cerebellar hypoplasia (13/19), absence of the cavum septum pellucidum (6/19), abnormalities of the corpus callosum (6/19), and microcephaly (3/19). Fetal MRI identified additional central nervous system features that were not appreciated on neurosonogram in eight cases. Single gene variants were reported in TUBA1A (13), TUBB (1), TUBB2A (1), TUBB2B (2), and TUBB3 (2).

CONCLUSION

The presence of ventriculomegaly with cerebellar abnormalities in conjunction with additional prenatal neurosonographic findings warrants additional evaluation for a tubulinopathy. Conclusive diagnosis can be achieved by molecular sequencing, which may assist in coordination, prognostication, and reproductive planning.

PRENATAL IMAGING FEATURES RELATED TO RAC3 PATHOGENIC VARIANT AND DIFFERENTIAL DIAGNOSES

This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved. What's already known about this topic? Six individuals between 5- and 19-year-old were reported with pathogenic variants in RAC3 responsible for brain malformations involving midline What does this study add? RAC3-fetopathy is associated with fetal akinesia deformation sequence, and complex brain malformations including corpus callosum agenesis, diencephalosynapsis, kinked brainstem, and vermian hypoplasia The differential diagnoses with prenatal kinked brainstem include fetopathies related to KIAA1109, L1CAM, Walker-Warburg syndrome and tubulinopathies. The present report adds the RAC3 related condition to this list.

Two different prenatal imaging cerebral patterns of tubulinopathy

To illustrate the prenatal cerebral imaging features associated with tubulinopathy, we report on five affected fetuses from unrelated families, with a de-novo heterozygous variant in a tubulin gene (TUBA1A, TUBB2B or TUBB3). We identified two distinct prenatal imaging patterns related to tubulinopathy: a severe form, characterized by enlarged germinal matrices, microlissencephaly and a kinked brainstem; and a mild form which has not been reported previously in the prenatal literature. The latter form is associated with non-specific features, including an asymmetric brainstem, corpus callosal dysgenesis, a lack of Sylvian fissure operculization and distortion of the anterior part of the interhemispheric fissure with subsequent impacted medial borders of the frontal lobes, the combination of which, in the absence of additional extracerebral anomalies, is highly suggestive of tubulinopathy. Copyright © 2020 ISUOG. Published by John Wiley & Sons Ltd.

KIAA1109 gene mutation in surviving patients with Alkuraya-Kučinskas syndrome: a review of literature

Background

Alkuraya-Kučinskas syndrome is an autosomal recessive disorder characterized by brain abnormalities associated with cerebral parenchymal underdevelopment, arthrogryposis, club foot and global developmental delay. KIAA1109, a functionally uncharacterized gene is identified as the molecular cause for Alkuraya-Kučinskas syndrome. Most of the reported mutations in KIAA1109 gene result in premature termination of pregnancies or neonatal deaths while a few mutations have been reported in surviving patients with global developmental delay and intellectual disability. To our knowledge, only three surviving patients from two families have been reported with missense variants in KIAA1109. In this study, we describe four surviving patients from two related families (a multiplex family) with global developmental delay and mild to severe intellectual disability with no other systemic manifestations. There were no miscarriages or neonatal deaths reported in these families.

Methods

X-chromosome exome panel sequencing was carried out in one patient and whole exome sequencing was carried out on the remaining three affected individuals and the unaffected father of the index family. Data analysis was carried out followed by variant filtering and segregation analysis. Sanger sequencing was carried out to validate the segregation of mutation in all four affected siblings and unaffected parents from both families.

Results

A novel homozygous missense mutation in a conserved region of KIAA1109 protein was identified. Sanger sequencing confirmed the segregation of mutation in both families in an autosomal recessive fashion.

Conclusion

Our study is the second study reporting a KIAA1109 variant in surviving patients with Alkuraya-Kučinskas syndrome. Our study expands the spectrum of phenotypic features and mutations associated with Alkuraya-Kučinskas syndrome.