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MAX
MYC associated transcriptional regulator X
MAX encodes a transcriptional regulator that partners with MYC family proteins to control genes involved in cell proliferation, differentiation, and apoptosis. The MAX gene provides instructions for making a protein that forms the core of a transcriptional network regulating cellular growth and division.
MAX is located on the long (q) arm of chromosome 14, at band 14q23.3. Arm ratio per GRCh38 - banding schematic.
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Overview
The MAX gene, located on chromosome 14, encodes a basic helix-loop-helix leucine zipper (bHLH-LZ) transcription factor that serves as an obligate partner for members of the MYC family of oncoproteins. MYC associated transcriptional regulator X, the protein product of MAX, binds to DNA as a homodimer or as a heterodimer with MYC, MAD, or MXD family proteins, allowing the cell to integrate signals about nutrient availability, growth factor stimulation, and stress into decisions about whether to proliferate, differentiate, or undergo programmed cell death.
Unlike many cancer predisposition genes that encode tumour suppressors or DNA repair proteins, MAX functions primarily as a transcriptional switch, determining whether target genes are activated or repressed depending on the partner protein with which it dimerises. Germline pathogenic variants in MAX disrupt this regulatory balance, leading to an autosomal dominant cancer syndrome characterised predominantly by phaeochromocytomas and paragangliomas-neuroendocrine tumours arising from chromaffin cells in the adrenal medulla or sympathetic and parasympathetic ganglia. Recognition of MAX as a cancer predisposition gene has led to its inclusion in multiple NHS Genomic Medicine Service clinical panels and the American College of Medical Genetics and Genomics secondary findings recommendations, reflecting its actionability for surveillance and management.
What the gene does
The MAX protein functions as a central node in a transcriptional regulatory network that governs fundamental cellular processes including proliferation, differentiation, metabolism, and survival. At the molecular level, MAX binds to specific DNA sequences known as E-box motifs (CACGTG) within the regulatory regions of target genes. The functional outcome of this binding depends critically on which partner protein accompanies MAX to the DNA.
When MAX forms heterodimers with MYC family proteins (c-MYC, N-MYC, or L-MYC), the complex functions as a transcriptional activator, recruiting co-activators and chromatin remodelling machinery to stimulate the expression of genes involved in cell cycle progression, ribosome biogenesis, protein synthesis, and glycolysis. Research suggests that MYC-MAX heterodimers activate thousands of target genes, effectively reprogramming cellular metabolism to support rapid growth and division. Conversely, when MAX partners with MAD or MXD family proteins, the resulting heterodimers act as transcriptional repressors, recruiting histone deacetylases and other co-repressors to silence the same E-box-containing genes that MYC-MAX activates.
This competitive partnership model allows cells to fine-tune their proliferative state in response to environmental cues. During periods of growth factor stimulation and abundant nutrients, MYC protein levels rise, favouring the formation of activating MYC-MAX complexes. When growth conditions deteriorate or differentiation signals are received, MAD family protein expression increases, shifting the equilibrium toward repressive MAD-MAX complexes. MAX itself is constitutively expressed and stable, serving as the constant anchor point around which this regulatory switch operates.
The protein also participates in additional regulatory mechanisms beyond simple activation or repression. Evidence suggests MAX homodimers can occupy E-box sites without strongly activating or repressing transcription, potentially serving a placeholder function that prevents inappropriate binding by other factors. The subcellular localisation of MAX is tightly regulated, with the protein shuttling between the nucleus and cytoplasm in response to cellular signals, providing an additional layer of control over its transcriptional activity. Disruption of normal MAX function through pathogenic variants can therefore have widespread effects on cellular behaviour, particularly in cell types such as chromaffin cells that are exquisitely sensitive to perturbations in growth control pathways.
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Chromosome location
The MAX gene is located on the long arm of chromosome 14 at position 14q23.3, a chromosomal region that contains several genes involved in development and cellular regulation. The gene spans a relatively compact genomic region, consistent with its role encoding a small but functionally critical transcription factor. This chromosomal location places MAX in proximity to other genes implicated in cellular growth and differentiation, though no specific positional effects or regulatory neighbourhoods have been definitively characterised for this locus. The gene's structural organisation reflects its evolutionary conservation, with the coding sequence showing remarkable similarity across mammalian species, underscoring the fundamental importance of MAX function in vertebrate biology.
Protein structure
The MAX protein comprises 160 amino acids organised into several functionally distinct regions that enable its role as a transcriptional regulator and heterodimerisation partner. The N-terminal region is disordered, lacking stable secondary structure and likely providing regulatory flexibility and sites for post-translational modifications that modulate MAX activity.
The core functional architecture centres on the basic helix-loop-helix (bHLH) domain. This domain contains a basic region responsible for sequence-specific DNA binding to E-box motifs, followed by two alpha helices separated by a loop structure. The basic region makes direct contact with the major groove of DNA, recognising the CACGTG sequence with high specificity, whilst the helix-loop-helix portion mediates protein-protein interactions essential for dimer formation.
Immediately adjacent to the bHLH domain lies the leucine zipper region. This region contains leucine residues positioned at regular intervals, creating a hydrophobic interface when the polypeptide adopts an alpha-helical conformation. The leucine zipper functions in concert with the HLH domain to stabilise both homodimers and heterodimers, providing the structural framework that determines partner selectivity. Research indicates that the combined bHLH-LZ architecture is essential for the protein's ability to discriminate between appropriate and inappropriate binding partners.
The C-terminal region is also disordered, lacking fixed structure in solution. Within this region sits a nuclear localisation signal motif, which directs the protein to the nucleus where it performs its transcriptional regulatory functions. The presence of extensive disordered regions flanking the structured central domain is characteristic of transcriptional regulators, allowing conformational flexibility that facilitates interactions with multiple partner proteins and regulatory complexes whilst maintaining the structural rigidity needed for specific DNA recognition.
Key variants
Pathogenic variants in MAX are relatively rare but have significant clinical consequences when they occur in the germline. The majority of disease-causing variants are loss-of-function alterations, including nonsense mutations that introduce premature stop codons, frameshift variants resulting from small insertions or deletions, and splice-site changes that disrupt normal transcript processing. These variants typically result in haploinsufficiency, where one functional copy of the gene is insufficient to maintain normal cellular regulation.
Missense variants affecting critical residues within the bHLH or leucine zipper domains have also been identified, often disrupting either DNA-binding capability or the protein's ability to form stable dimers with its regulatory partners. Some variants appear to interfere specifically with heterodimerisation whilst preserving the ability to form homodimers, leading to a dominant-negative effect whereby mutant MAX protein actively interferes with the function of the wild-type protein produced from the unaffected allele. The phenotypic consequences of MAX variants can vary depending on the specific molecular mechanism, though most pathogenic germline alterations share the common feature of dysregulating the MYC-MAX-MAD transcriptional network in susceptible cell types.
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.100A>T | p.Lys34Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Hereditary pheochromocytoma and paraganglioma |
c.200C>A | p.Ala67Asp | Pathogenic/Likely pathogenic | ★★☆☆ | Hereditary pheochromocytoma and paraganglioma |
c.223C>T | p.Arg75Ter | Pathogenic | ★★☆☆ | Hereditary cancer-predisposing syndrome |
c.228del | p.Asn78fs | Pathogenic | ★★☆☆ | Hereditary cancer-predisposing syndrome |
c.22G>T | p.Glu8Ter | Pathogenic | ★★☆☆ | Hereditary cancer-predisposing syndrome |
c.233dup | p.Asn78fs | Pathogenic/Likely pathogenic | ★★☆☆ | Hereditary cancer-predisposing syndrome |
c.271C>T | p.Gln91Ter | Pathogenic | ★★☆☆ | Hereditary cancer-predisposing syndrome |
c.289C>T | p.Gln97Ter | Pathogenic | ★★☆☆ | Hereditary pheochromocytoma and paraganglioma |
c.295+1G>A | - | Pathogenic | ★★☆☆ | Hereditary pheochromocytoma and paraganglioma |
c.295+1G>T | - | Pathogenic | ★★☆☆ | Hereditary cancer-predisposing 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
Germline pathogenic variants in MAX cause hereditary phaeochromocytoma and paraganglioma syndrome, an autosomal dominant condition characterised by the development of neuroendocrine tumours arising from chromaffin cells. Phaeochromocytomas develop in the adrenal medulla, whilst paragangliomas arise from extra-adrenal chromaffin tissue in sympathetic or parasympathetic ganglia distributed throughout the body, including the head, neck, thorax, abdomen, and pelvis.
Individuals with pathogenic MAX variants typically present with tumours that are often bilateral (affecting both adrenal glands) and may develop multiple paragangliomas. The tumours can cause symptoms related to excess catecholamine production, including sustained or episodic hypertension, headaches, palpitations, and excessive sweating. Some paragangliomas are non-secretory and present as masses detected incidentally or through symptoms related to local compression of surrounding structures. Research suggests that MAX-associated tumours may have distinctive biochemical and imaging characteristics compared to phaeochromocytomas and paragangliomas caused by variants in other predisposition genes, though considerable clinical heterogeneity exists even among carriers of the same variant within a family. Not all carriers develop tumours (incomplete penetrance), and the factors influencing individual risk remain under investigation.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic MAX variants typically follow autosomal dominant inheritance.
Each child has a 50% chance of inheriting the pathogenic variant, regardless of sex.
UK clinical status
MAX is recognised across multiple NHS Genomic Medicine Service panels, reflecting its established clinical significance in cancer predisposition. The gene holds green (high evidence) status on the Adult solid tumours cancer susceptibility panel and the Adult solid tumours for rare disease panel, acknowledging its role in hereditary tumour syndromes affecting adults. It also appears with green classification on the Childhood solid tumours panel (R359), recognising that whilst MAX-associated tumours most commonly present in adulthood, paediatric cases have been documented.
The gene's inclusion on the Inherited phaeochromocytoma and paraganglioma panel and the more focused Inherited phaeochromocytoma and paraganglioma excluding NF1 panel (R223) specifically reflects its mechanistic role in these neuroendocrine tumour types. MAX additionally features on the Multiple endocrine tumours panel and the Neuroendocrine cancer pertinent cancer susceptibility panel, consistent with the endocrine nature of the associated condition. Its presence on the Fetal anomalies panel (R21) and the Neurological segmental overgrowth panel reflects emerging recognition of the gene's potential involvement in developmental contexts, though these associations remain less well-characterised than the phaeochromocytoma-paraganglioma phenotype. MAX is designated as an ACMG SF v3.2 secondary finding gene (a US framework that informs but does not dictate UK practice) with Tier 1 actionability, reflecting international consensus on clinical utility. This means that pathogenic variants identified incidentally during genomic sequencing should be returned to patients due to the availability of effective surveillance and management strategies.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
For individuals with pathogenic MAX variants, lifestyle considerations centre primarily on managing cardiovascular risk and optimising conditions for tumour surveillance rather than on preventing tumour development through specific dietary or behavioural modifications. General population studies suggest that maintaining healthy blood pressure is important for overall cardiovascular health, which takes on particular relevance for individuals at risk of catecholamine-secreting tumours that can cause hypertension.
Some research in broader neuroendocrine contexts has examined whether dietary factors influence tumour behaviour, but no specific nutritional interventions have been demonstrated to prevent phaeochromocytoma or paraganglioma development in MAX variant carriers. A balanced diet supporting overall metabolic health remains a reasonable general approach, though individuals should discuss any significant dietary changes with their healthcare team, particularly given that some tumours can affect metabolism and nutritional status.
Stress management may be relevant insofar as physiological stress can influence catecholamine release, potentially exacerbating symptoms in individuals with functional tumours, though stress does not cause tumour formation. Regular physical activity offers general health benefits, though individuals with known or suspected phaeochromocytomas should discuss exercise plans with their clinical team, as uncontrolled catecholamine excess can create cardiovascular risks during vigorous exertion. Importantly, no lifestyle modification substitutes for recommended biochemical and imaging surveillance protocols, which remain the cornerstone of clinical management for MAX variant carriers.
Supplement considerations
There is no conclusive evidence that any dietary supplement prevents the development of phaeochromocytomas or paragangliomas in individuals with pathogenic MAX variants. The tumourigenesis in MAX-associated syndrome relates to disruption of fundamental transcriptional control mechanisms, and no nutritional compound has been shown to compensate for this genetic alteration or meaningfully reduce tumour risk.
Some individuals may be interested in antioxidant supplements given the general role of oxidative stress in cellular damage, but research has not established benefit for these compounds in preventing neuroendocrine tumours in MAX variant carriers. Similarly, whilst some studies in other contexts have examined whether specific vitamins or minerals influence cancer risk, these findings have not been replicated in the specific setting of hereditary phaeochromocytoma-paraganglioma syndromes.
Individuals with MAX variants who are considering any supplement should discuss this with their healthcare provider before starting, as some supplements can interact with medications or influence biochemical test results used in tumour surveillance. For example, certain compounds may theoretically affect catecholamine metabolism or interfere with imaging studies, though specific interactions have not been extensively documented. The most important preventive measure for MAX variant carriers remains adherence to recommended surveillance protocols rather than reliance on unproven nutritional interventions.
Frequently asked questions
What does the MAX gene do in normal cells?
MAX encodes a transcription factor that acts as a molecular switch controlling genes involved in cell growth and division. It partners with MYC proteins to activate growth-promoting genes or with MAD proteins to repress the same genes, allowing cells to adjust their proliferative state in response to environmental conditions.
How are MAX variants inherited?
MAX-associated phaeochromocytoma-paraganglioma syndrome follows an autosomal dominant inheritance pattern, meaning a pathogenic variant in one copy of the gene (inherited from either parent or occurring as a new mutation) is sufficient to increase tumour risk. Each child of an affected individual has a 50% chance of inheriting the variant.
What types of tumours are associated with MAX variants?
Pathogenic MAX variants predispose to phaeochromocytomas (tumours of the adrenal medulla) and paragangliomas (tumours arising from chromaffin tissue outside the adrenal glands). These neuroendocrine tumours can occur in the abdomen, pelvis, chest, or head and neck regions, and may produce excess catecholamines causing symptoms such as high blood pressure, headaches, and palpitations.
At what age do MAX-associated tumours typically develop?
MAX-associated phaeochromocytomas and paragangliomas often present in early to mid-adulthood, with a substantial proportion of tumours diagnosed in the third or fourth decade of life, though age of onset varies considerably. The wide variability in presentation makes it difficult to predict specific timing for any individual.
Why is MAX included in NHS genomic medicine panels?
MAX holds green (high evidence) status on multiple NHS panels, including those for inherited phaeochromocytoma-paraganglioma and adult solid tumours, because pathogenic variants in this gene have well-established associations with specific, clinically significant tumour types for which effective surveillance and management strategies exist.
Can lifestyle changes reduce tumour risk in MAX variant carriers?
No specific lifestyle modifications have been proven to prevent tumour development in individuals with pathogenic MAX variants, as tumourigenesis in this syndrome relates to disruption of fundamental cellular control mechanisms. General health measures supporting cardiovascular wellness are reasonable, but adherence to recommended biochemical and imaging surveillance protocols remains the most important preventive strategy.