PACS1 syndrome and the recurrent R203W mutation

PACS1 syndrome (also called Schuurs-Hoeijmakers syndrome, OMIM #615009) is an ultra-rare autosomal dominant neurodevelopmental disorder caused by mutations in the PACS1 gene (UniProt Q6VY07, NM_018026.4). It was first described by Schuurs-Hoeijmakers and colleagues in 2012.

Affected individuals typically present with:

• Intellectual disability (moderate to severe)
• Distinctive craniofacial features (low-set ears, downslanting palpebral fissures, hypertelorism, full lips, wide mouth)
• Pharmacoresistant epilepsy (in a majority of patients)
• Hypotonia
• Variable structural brain anomalies

The phenotype is recognizable enough that experienced geneticists often suggest the diagnosis clinically before molecular confirmation.

In approximately 98% of patients, the disease is caused by a single recurrent missense mutation:

The remaining ~2% of patients carry rarer missense variants in adjacent residues. This makes p.Arg203Trp one of the most striking examples of a single-allele genotype-phenotype correlation in dysmorphology.

There is no targeted therapy for PACS1 syndrome. Management is symptomatic:

• Epilepsy: a variety of antiepileptic drugs (AEDs) used empirically — phenytoin, carbamazepine, lamotrigine, levetiracetam, valproate, and benzodiazepines. Response varies widely between patients.
• Developmental support: early intervention, special education, physical and speech therapy.
• Surveillance: cardiac, ophthalmologic, endocrine.

The variability of AED response across patients suggests some drugs may interact with PACS1-R203W in a mutation-selective manner that contributes to clinical efficacy — beyond their canonical anti-seizure mechanism.

PACS1 is a trans-Golgi network adaptor protein that recognizes phosphorylated acidic clusters on cargo cytoplasmic tails, notably furin (Wan & Thomas 1998). The R203W substitution falls in the protein's Furin Binding Region (FBR) and produces a dominant-negative phenotype despite 50% normal protein remaining.

Recent work has implicated aberrant BICD2/dynein interaction (Krzysiak et al., 2026) and COL8A1 overproduction in patient fibroblasts (Bitoun & Trochet, 2025). The exact mechanism remains incompletely understood — which makes structural and pharmacological characterization especially valuable.