On this page
Major depressive disorder
MDD affects how a person thinks, feels, and behaves, and can lead to various emotional and physical problems. It is a common condition, with approximately 15% of people experiencing it during their lifetime, and often requires long-term management.
Overview
Major depressive disorder (MDD), often simply called depression, is a serious mood disorder that causes a persistent feeling of sadness and loss of interest. It affects a person's thoughts, feelings, behaviour, and physical health, interfering with daily activities such as working, sleeping, and eating [PMID:33675001]. Unlike temporary feelings of sadness or grief, MDD is a medical illness that lasts for an extended period, typically at least two weeks, and can significantly impact quality of life.
MDD is one of the most common mental health conditions, affecting millions of people worldwide. It is recognised as a leading cause of disability. The condition can manifest differently in individuals, with varying severities and combinations of symptoms, and can occur at any age, though it often begins in adolescence or early adulthood. While the exact causes are not fully understood, research suggests a combination of genetic, biological, environmental, and psychological factors contribute to its development.
Symptoms & clinical features
The symptoms of Major depressive disorder can be wide-ranging and vary from person to person. To be diagnosed with MDD, a person must experience a depressed mood or a loss of interest or pleasure in nearly all activities for most of the day, nearly every day, for at least two weeks. Alongside these core symptoms, other signs and symptoms may include significant changes in appetite or weight, changes in sleep patterns (insomnia or hypersomnia), and a noticeable slowing down of movements or speech, or increased restless activity [PMID:33675001].
Other common symptoms include fatigue or loss of energy, feelings of worthlessness or excessive guilt, difficulty thinking, concentrating, or making decisions, and recurrent thoughts of death or suicide. experiencing a few of these symptoms does not automatically mean a diagnosis of MDD; a healthcare professional assesses the overall pattern and impact of symptoms on an individual's life. Symptoms can affect a person's ability to function at work, school, or in social settings, leading to significant distress.
Video: Genetics 101
Affected organs
MDD primarily affects the brain and its functions, influencing mood, thought processes, and behaviour. It is understood to involve dysregulation in neurotransmitter systems, such as serotonin, dopamine, and noradrenaline, which are chemical messengers responsible for communication between brain cells. Structural and functional changes in certain brain regions, including the prefrontal cortex, hippocampus, and amygdala, have also been observed in individuals with MDD, though these are often subtle and complex.
While MDD is a mental health condition, its effects can extend to various physical systems due to the strong connection between the mind and body. For instance, changes in appetite and sleep can impact metabolic health and energy levels. Chronic stress associated with MDD may also influence the cardiovascular and immune systems, highlighting its systemic impact on overall health and well-being.
Risks & severity
Major depressive disorder exhibits a wide spectrum of severity, from mild episodes that may not significantly impair daily functioning to severe episodes with psychotic features that can be life-threatening. The lifetime risk of experiencing MDD is estimated to be around 15%, making it one of the most prevalent mental health conditions globally. The age of onset typically falls between late adolescence and mid-20s, but it can occur at any point in life, including childhood and older adulthood [PMID:33675001].
Risk factors for developing MDD include a family history of depression, significant life stressors (such as trauma, loss, or chronic illness), certain medical conditions, and substance misuse. Individuals who experience one episode of MDD are at an increased risk of future episodes. The severity and recurrence of depressive episodes often dictate the complexity of management required, ranging from psychological therapies for milder cases to a combination of medication and therapy for more severe or recurrent forms.
Genetic causes
Major depressive disorder is considered a polygenic or complex condition, meaning it arises from a combination of multiple genetic variations acting together, alongside environmental and lifestyle factors. Unlike single-gene disorders, there isn't one specific gene that directly causes MDD. Instead, many genes each contribute a small effect to an individual's susceptibility. Research has identified several genes that may play a role in influencing brain chemistry and function, thereby increasing the risk of developing MDD.
Some genes of interest include SLC6A4, which encodes the serotonin transporter protein that regulates the reuptake of serotonin in the brain. Variations in SLC6A4 have been associated with altered serotonin levels and responses to stress [PMID:35874426]. FKBP5, involved in the stress response system, and PCLO, which plays a role in neurotransmitter release, are also among the genes where certain variations have been linked to an increased risk of MDD, particularly in the context of adverse life events [PMID:28790278]. It is important to remember that these genetic factors only represent a predisposition, and environmental influences are also crucial in determining whether MDD develops.
Inheritance pattern
Major depressive disorder follows a polygenic or complex inheritance pattern. This means that a person's risk of developing MDD is influenced by variations in many different genes, each contributing a small effect. This genetic predisposition interacts with environmental factors, such as life experiences, stress, and lifestyle, to determine whether someone will develop the condition.
Because of this complex inheritance, MDD does not follow the clear patterns seen in single-gene disorders, such as autosomal dominant or recessive inheritance. If one family member has MDD, other family members may have an increased risk compared to the general population, but this risk is not absolute or easily predictable. This increased familial risk reflects the shared genetic background and potentially shared environmental factors within a family.
Diagnosis & testing
Diagnosing Major depressive disorder involves a comprehensive evaluation by a healthcare professional, typically a GP, psychiatrist, or mental health specialist. The diagnosis is based on specific clinical criteria outlined in diagnostic manuals, such as the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) or the International Classification of Diseases (ICD-10/11). This evaluation usually includes a detailed discussion of symptoms, medical history, family history, and an assessment of how the symptoms affect daily life. There are no laboratory tests or imaging scans that can definitively diagnose MDD.
Genetic testing for MDD is not currently used for routine diagnosis within the NHS Genomic Medicine Service, as MDD is a complex condition influenced by many genes and environmental factors. However, research into the genetic underpinnings of MDD is ongoing. Referral to specialist mental health services or clinical genetics may occur via a GP. For specific R-codes related to mental health conditions, a clinician would consult the NHS National Genomic Test Directory.
Management & lifestyle
Managing Major depressive disorder typically involves a personalised approach, often combining psychological therapies and medication, depending on the severity and individual circumstances. Psychological therapies, such as Cognitive Behavioural Therapy (CBT) and Interpersonal Therapy (IPT), can help individuals develop coping strategies and address underlying issues. Antidepressant medications, which aim to correct imbalances in brain chemistry, may be prescribed, often by a GP or psychiatrist. The choice of treatment is made in consultation with a healthcare professional.
Supportive measures, including lifestyle adjustments, can also be beneficial. These may include regular physical activity, maintaining a healthy diet, ensuring adequate sleep, and avoiding excessive alcohol or recreational drug use. Participation in support groups and establishing strong social connections can also play a role in recovery and ongoing well-being. Regular follow-up with healthcare providers is important to monitor symptoms and adjust treatment plans as needed within the NHS care pathway. Genetic counselling is generally not a primary management strategy for MDD itself, but may be relevant if there are concerns about other genetic conditions that could present with overlapping symptoms.
UK care pathway
In the UK, individuals concerned about Major depressive disorder typically begin by consulting their General Practitioner (GP). The GP can offer initial assessments, provide support, and refer to specialist mental health services if needed. These services may include talking therapies, community mental health teams, or psychiatric consultations. The NHS Genomic Medicine Service (GMS) primarily focuses on rare and inherited genetic conditions, and while research into the genetics of MDD is ongoing, direct genetic testing for MDD is not currently part of routine clinical diagnosis via GMS R-codes. Clinical genetics departments may be involved if there are complex family histories or suspected syndromic forms of depression. Genetic counsellors can provide information and support regarding the complex inheritance patterns of conditions like MDD.
Frequently asked questions
Is Major depressive disorder purely genetic?
No, Major depressive disorder is not purely genetic. It is considered a complex condition, meaning it arises from a combination of many genes interacting with environmental factors like stress, life experiences, and lifestyle. Genes can increase an individual's susceptibility, but they do not solely determine whether someone will develop the condition.
Can children get Major depressive disorder?
Yes, Major depressive disorder can affect children and adolescents, although their symptoms might present differently than in adults. For example, children might show irritability, school refusal, or physical complaints rather than overt sadness. Early diagnosis and intervention are important for children and young people.
What should I do if I think I or a family member has MDD?
If you are concerned about yourself or a family member, the first step is to speak with a General Practitioner (GP). They can provide an initial assessment, offer advice, and refer to appropriate mental health services for further evaluation and support within the NHS. There are also mental health charities and support organisations that can offer resources.
Will genetic testing tell me if I will get MDD?
Currently, genetic testing is not used to predict an individual's risk of developing Major depressive disorder. Because MDD is influenced by many genes and environmental factors, current genetic tests cannot provide a definitive 'yes' or 'no' answer. Research is ongoing to better understand the complex genetic contributions.
What is the difference between feeling sad and having MDD?
Feeling sad is a normal human emotion often triggered by life events, and it typically passes with time. Major depressive disorder, however, is a medical condition characterised by persistent sadness or loss of interest for at least two weeks, along with other significant symptoms that interfere with daily life and functioning. It often requires professional help to manage.
References
- Li Z, Ruan M, Chen J. Major Depressive Disorder: Advances in Neuroscience Research and Translational Applications. Neuroscience bulletin. 2021. PMID: 33582959
- Belmaker RH, Agam G. Major depressive disorder. The New England journal of medicine. 2008. PMID: 18172175
- Fava M, Kendler KS. Major depressive disorder. Neuron. 2000. PMID: 11144343
- Jiao W, Lin J, Deng Y. The immunological perspective of major depressive disorder: unveiling the interactions between central and peripheral immune mechanisms. Journal of neuroinflammation. 2025. PMID: 39828676
- Kennedy SH, Ceniti AK. Unpacking Major Depressive Disorder: From Classification to Treatment Selection. Canadian journal of psychiatry. Revue canadienne de psychiatrie. 2018. PMID: 29278937
- Jeoung SW, Park HS, Ryoo ZY. SUMOylation and Major Depressive Disorder. International journal of molecular sciences. 2022. PMID: 35887370
- Schechter LE. Major depressive disorder. Current pharmaceutical design. 2005. PMID: 15638754
- Major depressive disorder. Nature reviews. Disease primers. 2023. PMID: 37620379