| Gene Name | Gene Symbol | Chromosome Location | Protein Name | Protein Size | Protein Function | Common Pathogenic Variants | Variant Types | Mode of Inheritance | Penetrance | Key Molecular Pathways |
|---|---|---|---|---|---|---|---|---|---|---|
| ATP-binding cassette subfamily C member 6 | **ABCC6** | **16p13.11 / 16p13.1** | ABCC6 / MRP6 | **1503 aa**, ~**165–170 kDa** glycoprotein | ATP-dependent transmembrane efflux transporter, expressed predominantly in **liver** and **kidney**; promotes extracellular **ATP efflux**, which is converted by ENPP1 and CD73 to **PPi** and adenosine; major upstream regulator of anti-mineralization homeostasis (pqac-00000002, pqac-00000003, pqac-00000016, pqac-00000001) | Recurrent loss-of-function variants include **p.R1141X** and **del23-29 / g.del23-29**, together accounting for up to ~45% of pathogenic alleles in some cohorts; >300 variants reported overall, now ~400 in newer summaries (pqac-00000007, pqac-00000009, pqac-00000017) | Missense, nonsense, splice-site, small insertions/deletions, multiexon deletions/structural variants; predominantly **loss-of-function** (pqac-00000009, pqac-00000018, pqac-00000016) | **Autosomal recessive** PXE; ABCC6 variants can also cause some **GACI type 2** cases (pqac-00000003, pqac-00000011, pqac-00000015) | Generally high for **biallelic pathogenic variants** with **age-dependent** and **variable expressivity**; heterozygotes usually unaffected but may show subclinical or partial manifestations and elevated vascular calcification risk in some reports (pqac-00000018, pqac-00000006) | **ABCC6 → extracellular ATP efflux → ENPP1 → PPi + AMP → CD73/NT5E → adenosine; TNAP opposes PPi by hydrolysis; purinergic signaling / Pi:PPi balance / ectopic calcification inhibition** (pqac-00000001, pqac-00000015, pqac-00000016) |
| Ectonucleotide pyrophosphatase/phosphodiesterase 1 | **ENPP1** | **Not specified in retrieved PXE contexts** | ENPP1 / NPP1 | **Not specified in retrieved PXE contexts** | Principal ectoenzyme generating extracellular **PPi** from ATP; core anti-calcification enzyme downstream of ABCC6. ENPP1 deficiency causes classic **GACI**, and some ENPP1-mutated patients can present PXE-like features or overlap phenotypes (pqac-00000011, pqac-00000015, pqac-00000001) | Specific recurrent ENPP1 variants were **not detailed** in retrieved PXE contexts; disease-causing ENPP1 variants underlie most classic GACI and can overlap phenotypically with PXE (pqac-00000011, pqac-00000015) | Loss-of-function variants, including missense, nonsense, splice, and other disruptive alleles causing reduced/absent ENPP1 activity; exact spectrum not detailed in retrieved contexts (pqac-00000011, pqac-00000015) | **Autosomal recessive** for GACI; overlap with PXE spectrum recognized (pqac-00000004, pqac-00000015) | High for biallelic ENPP1 deficiency, but phenotype may range from severe infantile vascular calcification to PXE-like overlap; detailed penetrance not specified in retrieved contexts (pqac-00000004, pqac-00000015) | **Extracellular ATP hydrolysis to AMP + PPi**; central PPi-generating step in the **ABCC6–ENPP1–CD73–TNAP** pathway regulating ectopic mineralization (pqac-00000001, pqac-00000011, pqac-00000015) |
| 5'-nucleotidase ecto / CD73 | **NT5E** | **Not specified in retrieved PXE contexts** | CD73 | **Not specified in retrieved PXE contexts** | Converts **AMP to adenosine** in the extracellular space; adenosine indirectly inhibits calcification, in part by suppressing **TNAP**, thereby preserving PPi-mediated anti-calcification effects (pqac-00000001, pqac-00000015) | Specific recurrent NT5E pathogenic variants were **not detailed** in retrieved PXE contexts; NT5E mutations cause **CALJA/ACDC**, an overlapping ectopic calcification disorder (pqac-00000001, pqac-00000004, pqac-00000015) | Loss-of-function variants causing reduced/absent CD73 activity; exact variant spectrum not detailed in retrieved contexts (pqac-00000001, pqac-00000015) | **Autosomal recessive** for CALJA/ACDC; part of the PXE–GACI–CALJA disease continuum (pqac-00000001, pqac-00000004, pqac-00000015) | Detailed penetrance not specified in retrieved PXE contexts; phenotype is generally adult/late-onset in CALJA compared with PXE and GACI (pqac-00000004, pqac-00000015) | **AMP → adenosine**, with downstream reduction of **TNAP** activity and support of anti-mineralization purinergic signaling; final shared branch of the **ABCC6–ENPP1–CD73–TNAP** axis (pqac-00000001, pqac-00000015) |


*Table: This table summarizes the core genes and pathway biology relevant to pseudoxanthoma elasticum and related PPi-deficiency calcification disorders. It highlights ABCC6 as the primary PXE gene and places ENPP1 and NT5E within the shared extracellular ATP-PPi-adenosine anti-mineralization pathway.*