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.

Heterozygous loss of function of NR4A2 is associated with intellectual deficiency, rolandic epilepsy, and language impairment.

Recognition of a de novo mutation in NR4A2 associated with a neurodevelopmental phenotype reinforces its role in 2q23q24 microdeletion syndrome. Using the proband WES data and the probability of loss-of-function intolerance index (pLi) set at 1.0 (highest intolerance constraint), we could target NR4A2 as the candidate gene in this patient.