Research re-analysis of raw genomic data leads to the first described inherited case of CLDN5 in two brothers
Clinical Genetics and Therapeutics
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Primary Categories:
- Genomic Medicine
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Secondary Categories:
- Genomic Medicine
Introduction
The blood-brain barrier (BBB) is crucial for protecting the central nervous system by selectively regulating the passage of substances between the blood and the brain. Claudin-5 (CLDN5) is the most enriched tight junction protein at the BBB and plays a critical role in maintaining its integrity. While disruptions in CLDN5 expression have been linked to various neurological conditions, pathogenic variants in the CLDN5 coding sequence were not previously identified. Recent reports have described de novo variants in CLDN5 in unrelated individuals with microcephaly, pontine calcifications, and hemiplegia (Hashimoto et al., 2022), followed by a larger cohort showing developmental delay, seizures, microcephaly and brain calcifications (Deshwar et al., 2023). Here, we present the first familial case of CLDN5-related disease.
Case Presentation
Our index patient is a 10-year-old male who first presented at 4 months with partial complex seizures. He has a history of chronic static encephalopathy, global developmental delay, non-verbal status, non-ambulatory, focal impaired awareness epilepsy, microcephaly, brainstem and pons atrophy, central hypotonia, visual impairment, and G-tube dependence. His younger brother, a 7-year-old male, presented at 9 months with seizure onset, intractable epilepsy, developmental regression, hemiparesis, global delay, hypotonia, G-tube dependence, and cerebral palsy. Family history includes a healthy, unaffected female sibling, an unaffected mother, and a father with ADHD. No consanguinity is reported.
Diagnostic Workup
Whole exome sequencing, chromosomal microarray, and additional tests, including Episeek and Episign, were performed on both brothers and were unrevealing. Metabolic screenings (organic acids, plasma amino acids, acylcarnitine, lysosomal storage disease) were also negative. Whole genome sequencing was performed as a quad and initially showed no pathogenic findings. However, re-analysis identified a novel heterozygous missense variant in CLDN5 (c.176C>T, p.T591) in both affected brothers. Parental analysis revealed the same variant in the father at low-level mosaicism, confirmed by Sanger sequencing. While the father has a mild neurological phenotype with ADHD, the presence of the variant warrants further imaging as subtle changes may be evident.
Discussion
Previous reports of CLDN5 mutations have shown a phenotype overlapping with our patients, including seizures, microcephaly, brain calcifications, and developmental delay. Zebrafish models for variants analougous to our patients showed that loss of CLDN5 in zebraship resulted in BBB disruption, growth restriction, and seizure-like activity. Similarly, overexpression of patient-derived variants led to impaired embryogenesis and defective tight junction formation, supporting the hypothesis that these variants disrupt normal BBB function (Deshwar et al, 2023). The variant in our patients (p.T591) is located near the recurrent c.178G>C variant that has been described in 4 of ~20 cases in the literature. Notably, individuals with the p.Gly60Arg mutation, were the only ones to achieve independent ambulation or meaningful speech, which mimics the phenotype of our patients, suggesting a potential genotype-phenotype correlation.
Conclusion
Previous reports of CLDN5 mutations have shown a phenotype overlapping with our patients, including seizures, microcephaly, brain calcifications, and developmental delay. Zebrafish models for variants analougous to our patients showed that loss of CLDN5 in zebraship resulted in BBB disruption, growth restriction, and seizure-like activity. Similarly, overexpression of patient-derived variants led to impaired embryogenesis and defective tight junction formation, supporting the hypothesis that these variants disrupt normal BBB function (Deshwar et al, 2023). The variant in our patients (p.T591) is located near the recurrent c.178G>C variant that has been described in 4 of ~20 cases in the literature. Notably, individuals with the p.Gly60Arg mutation, were the only ones to achieve independent ambulation or meaningful speech, which mimics the phenotype of our patients, suggesting a potential genotype-phenotype correlation.
The blood-brain barrier (BBB) is crucial for protecting the central nervous system by selectively regulating the passage of substances between the blood and the brain. Claudin-5 (CLDN5) is the most enriched tight junction protein at the BBB and plays a critical role in maintaining its integrity. While disruptions in CLDN5 expression have been linked to various neurological conditions, pathogenic variants in the CLDN5 coding sequence were not previously identified. Recent reports have described de novo variants in CLDN5 in unrelated individuals with microcephaly, pontine calcifications, and hemiplegia (Hashimoto et al., 2022), followed by a larger cohort showing developmental delay, seizures, microcephaly and brain calcifications (Deshwar et al., 2023). Here, we present the first familial case of CLDN5-related disease.
Case Presentation
Our index patient is a 10-year-old male who first presented at 4 months with partial complex seizures. He has a history of chronic static encephalopathy, global developmental delay, non-verbal status, non-ambulatory, focal impaired awareness epilepsy, microcephaly, brainstem and pons atrophy, central hypotonia, visual impairment, and G-tube dependence. His younger brother, a 7-year-old male, presented at 9 months with seizure onset, intractable epilepsy, developmental regression, hemiparesis, global delay, hypotonia, G-tube dependence, and cerebral palsy. Family history includes a healthy, unaffected female sibling, an unaffected mother, and a father with ADHD. No consanguinity is reported.
Diagnostic Workup
Whole exome sequencing, chromosomal microarray, and additional tests, including Episeek and Episign, were performed on both brothers and were unrevealing. Metabolic screenings (organic acids, plasma amino acids, acylcarnitine, lysosomal storage disease) were also negative. Whole genome sequencing was performed as a quad and initially showed no pathogenic findings. However, re-analysis identified a novel heterozygous missense variant in CLDN5 (c.176C>T, p.T591) in both affected brothers. Parental analysis revealed the same variant in the father at low-level mosaicism, confirmed by Sanger sequencing. While the father has a mild neurological phenotype with ADHD, the presence of the variant warrants further imaging as subtle changes may be evident.
Discussion
Previous reports of CLDN5 mutations have shown a phenotype overlapping with our patients, including seizures, microcephaly, brain calcifications, and developmental delay. Zebrafish models for variants analougous to our patients showed that loss of CLDN5 in zebraship resulted in BBB disruption, growth restriction, and seizure-like activity. Similarly, overexpression of patient-derived variants led to impaired embryogenesis and defective tight junction formation, supporting the hypothesis that these variants disrupt normal BBB function (Deshwar et al, 2023). The variant in our patients (p.T591) is located near the recurrent c.178G>C variant that has been described in 4 of ~20 cases in the literature. Notably, individuals with the p.Gly60Arg mutation, were the only ones to achieve independent ambulation or meaningful speech, which mimics the phenotype of our patients, suggesting a potential genotype-phenotype correlation.
Conclusion
Previous reports of CLDN5 mutations have shown a phenotype overlapping with our patients, including seizures, microcephaly, brain calcifications, and developmental delay. Zebrafish models for variants analougous to our patients showed that loss of CLDN5 in zebraship resulted in BBB disruption, growth restriction, and seizure-like activity. Similarly, overexpression of patient-derived variants led to impaired embryogenesis and defective tight junction formation, supporting the hypothesis that these variants disrupt normal BBB function (Deshwar et al, 2023). The variant in our patients (p.T591) is located near the recurrent c.178G>C variant that has been described in 4 of ~20 cases in the literature. Notably, individuals with the p.Gly60Arg mutation, were the only ones to achieve independent ambulation or meaningful speech, which mimics the phenotype of our patients, suggesting a potential genotype-phenotype correlation.