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AP4M1
adaptor related protein complex 4 subunit mu 1
The AP4M1 gene provides instructions for a protein that is a critical component of the adaptor protein complex 4 (AP-4), involved in intracellular protein trafficking and membrane sorting. AP4M1 encodes the μ1 subunit of the AP-4 complex, which plays a vital role in directing specific proteins to their correct locations within a cell.
AP4M1 is located on the long (q) arm of chromosome 7, at band 7q22.1. Arm ratio per GRCh38 - banding schematic.
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Overview
The AP4M1 gene, also known as adaptor-related protein complex 4 subunit mu 1, is essential for the proper functioning of cells, particularly within the nervous system. It produces a protein that is part of a larger complex, AP-4, which helps to sort and transport other proteins within the cell. This complex ensures that proteins reach their correct cellular destinations, a process crucial for maintaining cellular health and normal neurological function.
Disruptions to the AP4M1 gene or its protein product can impair this vital transport system, leading to the accumulation of certain proteins in incorrect locations. Such cellular dysfunction is implicated in the development of various neurological disorders.
What the gene does
The AP4M1 gene encodes the μ1 subunit of the adaptor protein complex 4 (AP-4). This complex is one of five known adaptor protein complexes, all of which are heterotetramers, meaning they are composed of four different protein subunits. The primary function of AP-4 is to regulate the movement of specific membrane proteins from the trans-Golgi network to endosomes and lysosomes, or from the endosomes to the cell surface.
This precise trafficking ensures that proteins involved in critical cellular processes, such as nutrient sensing and waste degradation, are delivered to the correct organelles. The μ1 subunit, encoded by AP4M1, is thought to be involved in cargo recognition, helping the AP-4 complex identify which proteins need to be transported. Proper functioning of AP4M1 and the AP-4 complex is therefore fundamental for cellular homeostasis and neuronal integrity, as evidenced by the neurological consequences of its dysfunction.
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Chromosome location
The AP4M1 gene is located on the long arm of chromosome 7 at position 7q22.1. This specific genomic address helps to identify its precise location within the human genome and is used in genetic mapping and research. The gene includes several exons, which are the coding regions that provide the instructions for building the AP4M1 protein.
Protein structure
The protein encoded by the AP4M1 gene is 453 amino acids long and forms a crucial part of the AP-4 complex. This protein contains a significant MHD domain, spanning amino acids 184-452. This domain is thought to be important for the protein's overall structure and its interaction with other components of the AP-4 complex, as well as with the specific cargo proteins it helps to transport.
Key variants
Genetic variations, or variants, in the AP4M1 gene can affect the structure and function of the AP4M1 protein. These changes can range from single nucleotide substitutions to larger deletions or insertions within the gene sequence. Depending on their nature and location, such variants may lead to a non-functional or improperly functioning AP4M1 protein, thereby disrupting the critical protein trafficking pathway coordinated by the AP-4 complex.
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.10C>T | p.Gln4Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Hereditary spastic paraplegia 50 |
c.1117C>T | p.Gln373Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Intellectual disability |
c.1129del | p.Leu377fs | Pathogenic/Likely pathogenic | ★★☆☆ | not provided |
c.1137+1G>T | - | Pathogenic/Likely pathogenic | ★★☆☆ | Hereditary spastic paraplegia 50 |
c.1317G>A | p.Trp439Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Hereditary spastic paraplegia 50 |
c.142del | p.Val48fs | Pathogenic/Likely pathogenic | ★★☆☆ | Hereditary spastic paraplegia 50 |
c.218dup | p.Asn73fs | Pathogenic | ★★☆☆ | Hereditary spastic paraplegia 50 |
c.547C>T | p.Gln183Ter | Pathogenic | ★★☆☆ | Hereditary spastic paraplegia 50 |
c.802C>T | p.Arg268Ter | Pathogenic | ★★☆☆ | Hereditary spastic paraplegia 50 |
c.916C>T | p.Arg306Ter | Pathogenic | ★★☆☆ | Hereditary spastic paraplegia |
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
Variants in the AP4M1 gene are associated with a group of neurological disorders, most notably Spastic paraplegia type 47-52 (AP-4 complex) (AR). These conditions are typically inherited in an autosomal recessive manner. Individuals with these conditions often experience progressive stiffness and weakness in the leg muscles (spasticity), leading to difficulties with walking, balance, and coordination. Other neurological symptoms, such as intellectual disability and seizures, can also be present, reflecting the widespread importance of AP-4 in neuronal function.
- Spastic paraplegia type 47-52 (AP-4 complex) Dedicated page coming soon
UK clinical status
The AP4M1 gene is included in several NHS England Genomic Medicine Service clinical panels, reflecting its established role in inherited neurological disorders. It is featured on green-rated panels for Childhood onset hereditary spastic paraplegia, Hereditary spastic paraplegia, and Intellectual disability. This inclusion indicates that AP4M1 is a gene for which there is strong evidence for disease causation and clinical utility in diagnostic testing within the UK healthcare system, as assessed by PanelApp.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the main function of the AP4M1 gene?
The AP4M1 gene provides instructions for the μ1 subunit of the adaptor protein complex 4 (AP-4), which is essential for sorting and transporting specific proteins within cells, particularly from the Golgi network to endosomes and lysosomes.
What conditions are associated with AP4M1 variants?
Variants in the AP4M1 gene are primarily associated with forms of hereditary spastic paraplegia, such as Spastic paraplegia type 47-52, which is characterised by progressive muscle stiffness and weakness.
How is AP4M1 typically inherited?
Conditions related to AP4M1 variants, such as certain forms of spastic paraplegia, are generally inherited in an autosomal recessive manner. This means that an individual must inherit two altered copies of the gene (one from each parent) to develop the condition.