Variants in CLDN5 cause a syndrome characterized by seizures, microcephaly and brain calcifications.

The blood-brain barrier ensures CNS homeostasis and protection from injury. Claudin-5 (CLDN5), an important component of tight junctions, is critical for the integrity of the blood-brain barrier. We have identified de novo heterozygous missense variants in CLDN5 in 15 unrelated patients who presented with a shared constellation of features including developmental delay, seizures (primarily infantile onset focal epilepsy), microcephaly and a recognizable pattern of pontine atrophy and brain calcifications. All variants clustered in one subregion/domain of the CLDN5 gene and the recurrent variants demonstrate genotype-phenotype correlations. We modelled both patient variants and loss of function alleles in the zebrafish to show that the variants analogous to those in patients probably result in a novel aberrant function in CLDN5. In total, human patient and zebrafish data provide parallel evidence that pathogenic sequence variants in CLDN5 cause a novel neurodevelopmental disorder involving disruption of the blood-brain barrier and impaired neuronal function.

A Chrnb3-Cre BAC transgenic mouse line for manipulation of gene expression in retinal ganglion cells.

The mechanisms by which retinal ganglion cells (RGCs) make specific connections during development is an intense area of research and have served as a model for understanding the general principles of circuit wiring. As such, genetic tools allowing for specific recombination in RGCs are critical to further our understanding of the cell-specific roles of different genes during these processes. However, many RGC-specific Cre lines have drawbacks, due to their broad expression in other cell types and/or retinorecipient regions or lack of expression in broad swaths of the retina. Here, we characterize a Cre BAC transgenic line driven by elements of the cholinergic receptor nicotinic beta 3 subunit (Chrnb3). We show that Cre expression is restricted to RGCs in the retina and sparsely expressed in the brain, importantly excluding retinorecipient regions. Furthermore, Chrnb3-Cre mice label a wide variety of RGCs distributed throughout the retina and Cre activity is detected embryonically, shortly following RGC differentiation. Finally, we find that Chrnb3-Cre-labeled RGCs innervate multiple retinorecipient areas that serve both image-forming and nonimage forming functions. Thus, this genetic tool will be of broad use to investigators studying the RGC-specific contributions of genes to visual circuit development.