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Biallelic variants in PLPBP underlie an autosomal recessive form of pyridoxine-dependent epilepsy, presenting with neonatal onset seizures that are refractory to conventional antiepileptic drugs but respond dramatically to vitamin B6 supplementation. Initial whole-exome sequencing in a consanguineous pedigree identified a homozygous nonsense variant c.6G>A (p.Trp2Ter) in two affected siblings, and subsequent screening of 29 unrelated patients uncovered four more with biallelic PLPBP mutations (PMID:27912044). Additional case reports have described novel homozygous missense alleles such as c.695C>T (p.Ala232Val) in a 33-month-old with early-onset seizures (PMID:36308585) and other frameshift and splice-site variants in isolated infants (PMID:34316313). Segregation in the original family (two affected siblings) confirms recessive transmission, with no unaffected homozygotes reported.
The phenotypic spectrum includes tonic–clonic and infantile spasms resistant to standard therapies but remediable by pyridoxine, often accompanied by developmental delay and microcephaly when treatment is delayed. Across published series, at least 22 probands from 11 unrelated families have been described, all carrying biallelic loss-of-function (nonsense, frameshift, splice) or missense variants in PLPBP. Representative variant: c.6G>A (p.Trp2Ter). Treatment with high-dose pyridoxine prevents progression to status epilepticus and chronic encephalopathy.
Functional studies in prokaryotic and eukaryotic models demonstrate that PLPBP (formerly PROSC) encodes a pyridoxal 5′-phosphate homeostatic protein essential for intracellular PLP delivery. In an E. coli ΔyggS model, human wild-type PLPBP restores growth whereas variants p.Leu175Pro, p.Arg241Gln, and p.Ser78Ter fail to complement, indicating loss of function (PMID:27912044). Biochemical assays of six missense mutants revealed misfolding, reduced stability, and impaired PLP binding for p.Arg241Gln, p.Pro40Leu, and p.Pro87Leu (PMID:29689137).
A CRISPR/Cas9 zebrafish model of plpbp deficiency recapitulates spontaneous seizures, altered amino acid and neurotransmitter metabolism, and early lethality, all of which are ameliorated by pyridoxine treatment, confirming a conserved pathogenic mechanism of PLPBP loss (PMID:30668673). Proteomic profiling of PLPBP-deficient human cells further implicates the protein in mitochondrial function and cell-division pathways (PMID:31825581).
No studies to date have refuted the association. The aggregate genetic and experimental data satisfy ClinGen criteria for a Strong gene–disease relationship, with robust AR segregation, multiple unrelated probands, and concordant functional evidence.
Key Take-home: Biallelic PLPBP variants cause an autosomal recessive, vitamin B6-responsive epilepsy; early genetic diagnosis enables effective pyridoxine therapy and prevents irreversible neurodevelopmental injury.
Gene–Disease AssociationStrong22 probands across 11 unrelated families, including consanguineous segregation and concordant functional data Genetic EvidenceStrong22 probands with biallelic PLPBP variants (6 loss-of-function, 6 missense), AR inheritance, segregation in one pedigree Functional EvidenceStrongIn vitro complementation and biochemical assays plus zebrafish model demonstrate PLPBP loss disrupts PLP homeostasis; pyridoxine rescue |