We describe a third patient with brain small vessel disease 3 (BSVD3), being the first with a homozygous essential splice site variant in the COLGALT1 gene, with a more severe phenotype than the 2 children reported earlier.
Analysis of whole exome sequencing (WES) data of the child and parents was performed. We validated the missplicing of the homozygous variant using reverse transcription PCR and Sanger sequencing of the mRNA in a lymphocyte culture.
The patient presented antenatally with porencephaly on ultrasound and MRI. Postnatally, he showed a severe developmental delay, refractory epilepsy, spastic quadriplegia, and a progressive hydrocephalus. WES revealed a homozygous canonical splice site variant NM_024656.3:c.625-2A>C. PCR and Sanger sequencing of the mRNA demonstrated that 2 cryptic splice sites are activated, causing a frameshift in the major transcript and in-frame deletion in a minor transcript.
We report a third patient with biallelic pathogenic variants in COLGALT1, confirming the role of this gene in autosomal recessive BSVD3.