The KIAA0196 gene (now officially known as WASHC5, WASH Complex Subunit 5, also called Strumpellin) encodes a core component of the WASH complex that regulates endosomal protein sorting and recycling. Mutations cause autosomal dominant hereditary spastic paraplegia type 8 (SPG8).
The KIAA0196/WASHC5 gene is located on chromosome 8q24.13 and encodes strumpellin, a 1,159-amino acid protein that forms part of the WASH (Wiskott-Aldrich syndrome protein and SCAR homolog) complex[1]. The WASH complex regulates actin polymerization on endosomes, which is essential for the tubular recycling of membrane proteins including receptors and transporters[2]. Heterozygous missense mutations cause SPG8, a pure form of autosomal dominant hereditary spastic paraplegia (HSP) characterized by progressive spasticity of the lower limbs due to corticospinal tract degeneration[3]. [1]
| | | [2]
|---|---| [3]
| Gene Symbol | WASHC5 (formerly KIAA0196) |
| Full Name | WASH Complex Subunit 5 (Strumpellin) |
| Aliases | KIAA0196, SPG8, Strumpellin |
| Chromosomal Location | 8q24.13 |
| NCBI Gene ID | 9744 |
| OMIM | 610657 |
| Ensembl | ENSG00000104523 |
| UniProt | Q12768 |
| Associated Diseases | SPG8 (hereditary spastic paraplegia type 8) |
Strumpellin is one of five core subunits of the WASH complex[2]:
| Subunit | Gene | Function |
|---|---|---|
| WASH1 | WASHC1 | Arp2/3 activator; nucleates actin on endosomes |
| FAM21 | WASHC2 | Connects WASH complex to retromer via VPS35 |
| CCDC53 | WASHC3 | Structural subunit |
| SWIP | WASHC4 | Structural subunit |
| Strumpellin | WASHC5 (KIAA0196) | Structural/regulatory subunit; connects to VAMP-associated proteins |
The WASH complex nucleates branched actin filaments on endosomal membranes, creating force for membrane tubulation and cargo sorting[2].
Strumpellin is essential for proper endosomal recycling[4]:
In neurons, endosomal recycling is critical for[3]:
SPG8 is a pure autosomal dominant HSP caused by WASHC5 mutations[3]:
| Feature | Description |
|---|---|
| Inheritance | Autosomal dominant |
| Onset | Variable (childhood to 5th decade, mean ~30-40 years) |
| Core feature | Progressive spastic paraparesis (lower limb spasticity) |
| Gait | Scissoring gait, hyperreflexia, extensor plantar responses |
| Upper limbs | Usually spared (pure HSP) |
| Bladder | Urinary urgency common |
| Cognition | Usually preserved |
| Neuropathology | Corticospinal tract (axonal) degeneration, length-dependent |
SPG8-causing mutations impair strumpellin function through[4]:
Endosomal dysfunction in SPG8 parallels mechanisms in[5]:
| Variant | Effect | Phenotype |
|---|---|---|
| V626F | Missense | SPG8 (original family) |
| L619F | Missense | SPG8 |
| N471D | Missense | SPG8 |
| E532K | Missense | SPG8 (late onset) |
| R583H | Missense | SPG8 |
Most SPG8 variants are missense mutations clustering in the central region of strumpellin, suggesting this region is critical for WASH complex function or protein interactions[3].
WASHC5 is ubiquitously expressed with high levels in the nervous system[1]:
Derivery E et al. The Arp2/3 activator WASH controls the fission of endosomes through a large multiprotein complex (2009). 2009. ↩︎
Freeman C et al. The hereditary spastic paraplegia protein strumpellin: characterisation in neurons and of the effect of disease mutations on WASH complex assembly and function (2015). 2015. ↩︎
McGough IJ et al. Retromer binding to FAM21 and the WASH complex is perturbed by the Parkinson disease-linked VPS35(D620N) mutation (2014). 2014. ↩︎