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INPP5E
inositol polyphosphate-5-phosphatase E
INPP5E is located on the long (q) arm of chromosome 9, at band 9q34.3. Arm ratio per GRCh38 - banding schematic.
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Overview
INPP5E is located on chromosome 9 and provides instructions for making inositol polyphosphate-5-phosphatase E, a specialised enzyme that functions within the primary cilium. Primary cilia are hair-like projections found on most human cells that act as signalling hubs, detecting extracellular cues and coordinating cellular responses during development and tissue maintenance.
The INPP5E protein regulates the levels of specific phosphoinositide lipids within the ciliary membrane, which is essential for maintaining cilium structure and enabling proper signal transduction through pathways such as Sonic Hedgehog. Loss of INPP5E function disrupts these processes, leading to a spectrum of ciliopathy phenotypes. Pathogenic variants are inherited in an autosomal recessive pattern, meaning affected individuals carry two altered copies of the gene, one from each parent.
What the gene does
INPP5E functions as a phosphatase enzyme that removes a phosphate group from the 5-position of the inositol ring in phosphatidylinositol lipids, specifically converting phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate to their respective monophosphate forms. This activity is crucial for controlling the phosphoinositide composition of the ciliary membrane.
The enzyme localises predominantly to the primary cilium, where it maintains the distinct lipid environment required for ciliary membrane integrity and receptor trafficking. By regulating phosphoinositide levels, INPP5E influences multiple signalling cascades including Sonic Hedgehog signalling, which directs neural tube patterning, limb development, and cerebellar formation during embryogenesis. The protein also affects trafficking of membrane proteins into and out of the cilium, ensuring that signalling receptors are correctly positioned.
Dysregulation of INPP5E phosphatase activity leads to abnormal accumulation of specific phosphoinositides within cilia, disrupting ciliary membrane architecture and impairing the cell's ability to interpret developmental signals. This results in the multisystem developmental defects characteristic of ciliopathies.
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Chromosome location
INPP5E is located at chromosomal position 9q34.3, near the telomeric end of the long arm of chromosome 9. The gene spans genomic sequence encoding a 644-amino-acid protein. This chromosomal region has been linked to ciliopathy phenotypes through genetic mapping studies in affected families.
Protein structure
The INPP5E protein comprises 644 amino acids with a distinctive domain organisation. The N-terminal region (amino acids 1-193) is disordered, lacking fixed three-dimensional structure, which may allow flexible interactions with binding partners or regulatory molecules.
A prominent structural feature is the presence of 13 short repeats following a P-X-X-P motif (where X represents any amino acid), spanning amino acids 10-242. These repeats include: repeat 1 (residues 10-13), repeat 2 (15-18), repeat 3 (28-31), repeat 4 (39-42), repeat 5 (55-58), repeat 6 (69-71), repeat 7 (72-74), repeat 8 (75-78), repeat 9 (121-124), repeat 10 (169-172), repeat 11 (183-185), repeat 12 (190-193), and repeat 13 (236-239). These proline-rich repeats may mediate protein-protein interactions or contribute to structural organisation within the cilium.
The C-terminal portion of the protein contains the catalytic phosphatase domain responsible for the enzyme's inositol polyphosphate-5-phosphatase activity, enabling the specific removal of the 5-phosphate from substrate lipids.
Key variants
Pathogenic variants in INPP5E are typically loss-of-function alterations that abolish or severely reduce phosphatase enzymatic activity. These include nonsense variants introducing premature stop codons, frameshift variants caused by small insertions or deletions, and missense variants affecting critical catalytic residues within the phosphatase domain. Because INPP5E-related conditions follow autosomal recessive inheritance, affected individuals carry pathogenic variants on both gene copies, while carriers with one altered copy generally remain asymptomatic.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1253_1256del | p.Phe418fs | Pathogenic/Likely pathogenic | ★★☆☆ | MORM syndrome |
c.1303C>T | p.Arg435Trp | Pathogenic | ★★☆☆ | Joubert syndrome 1 |
c.1565G>C | p.Gly522Ala | Pathogenic/Likely pathogenic | ★★☆☆ | Joubert syndrome and related disorders |
c.1629C>G | p.Tyr543Ter | Pathogenic | ★★☆☆ | INPP5E-related disorder |
c.1670G>A | p.Arg557His | Pathogenic/Likely pathogenic | ★★☆☆ | INPP5E-related disorder |
c.1753C>T | p.Arg585Cys | Pathogenic/Likely pathogenic | ★★☆☆ | Joubert syndrome |
c.1784_1787del | p.Val595fs | Pathogenic | ★★☆☆ | Joubert syndrome |
c.1861C>T | p.Arg621Trp | Pathogenic/Likely pathogenic | ★★☆☆ | MORM syndrome |
c.1862G>A | p.Arg621Gln | Pathogenic/Likely pathogenic | ★★☆☆ | Joubert syndrome and related disorders |
c.2_10del | p.Met1_Ser3del | Pathogenic/Likely pathogenic | ★★☆☆ | Joubert syndrome |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in INPP5E cause a spectrum of autosomal recessive ciliopathy syndromes characterised by variable combinations of neurological, ocular, renal, and skeletal abnormalities. These conditions reflect the critical role of primary cilia in orchestrating developmental signalling across multiple organ systems. Clinical presentations range from severe multisystem involvement affecting survival to milder phenotypes with isolated features such as retinal degeneration or polydactyly. The severity and specific pattern of features depend on the nature and position of the pathogenic variants as well as potential modifier genes.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic INPP5E variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
INPP5E is recognised on multiple NHS Genomic Medicine Service gene panels with green (diagnostic-grade) evidence ratings, reflecting its established role in rare genetic conditions. The gene appears on the DDG2P panel for developmental disorders, the Fetal anomalies panel (R21), the Intellectual disability panel (R29), and several ciliopathy-focused panels including Neurological ciliopathies, Ophthalmological ciliopathies, Rare multisystem ciliopathy disorders, and Renal ciliopathies. It is also included on the Retinal disorders panel (R32) and Structural eye disease panel (R36), underscoring the importance of INPP5E variants in both syndromic and isolated ocular phenotypes within the NHS diagnostic pathway.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What does it mean to be a carrier of an INPP5E variant?
Carriers have one pathogenic variant in INPP5E and one typical copy, which is generally sufficient for normal ciliary function. Carriers do not typically develop symptoms but can pass the variant to their children. If both parents are carriers, each child has a 25% chance of inheriting two pathogenic variants and being affected.
How do INPP5E variants cause multiple organ problems?
INPP5E variants disrupt phosphoinositide balance within primary cilia, which are present on cells throughout the body and coordinate developmental signalling pathways. When ciliary signalling is impaired during embryonic development, multiple organ systems that rely on these pathways - including the brain, eyes, kidneys, and skeleton - can be affected.
Are all INPP5E-related conditions severe?
No, there is significant phenotypic variability. Some individuals present with severe multisystem involvement, whilst others have milder presentations such as isolated retinal degeneration or polydactyly. The specific variants inherited and potential modifying genetic factors influence clinical severity.