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18p deletion syndrome
Also known as monosomy 18p · de Grouchy syndrome type 1
This syndrome can lead to a range of developmental and physical challenges, including intellectual disability, growth delays, and distinctive facial features. It affects individuals from birth and is typically diagnosed in childhood.
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Overview
18p deletion syndrome, also known as monosomy 18p or de Grouchy syndrome type 1, is a rare genetic disorder. It occurs when there is a missing segment of genetic material on the short arm (p arm) of chromosome 18. This missing genetic information can vary in size and location, leading to a spectrum of signs and symptoms among affected individuals [PMID:33676208].
The syndrome affects approximately 1 in 50,000 live births. It is considered a chromosomal disorder because it involves a change in the number or structure of chromosomes, which are structures within cells that contain our genes. The loss of genetic material from chromosome 18 can impact the development of many different body systems.
Symptoms & clinical features
The clinical features of 18p deletion syndrome can be quite varied, meaning that not all individuals will experience the same symptoms, or with the same severity. Common characteristics often include developmental delay, which can manifest as delays in reaching developmental milestones such as walking and talking [PMID:28751543]. Intellectual disability is also frequently observed, ranging from mild to moderate.
Physical features may include a range of distinctive facial characteristics. These can involve widely spaced eyes (hypertelorism), a broad or flat nasal bridge, a small mouth, and drooping eyelids (ptosis). Other potential features include a short neck, small hands and feet, and low-set ears. Some individuals may also experience growth delays, leading to short stature.
Individuals with 18p deletion syndrome may also present with various medical issues. These can include heart defects, kidney problems, and issues with the immune system. Psychiatric or behavioural concerns, such as anxiety or attention difficulties, have also been reported in some cases [PMID:28751543]. The specific symptoms depend on the exact genes lost in the deleted region of chromosome 18.
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Affected organs
18p deletion syndrome can affect multiple organ systems throughout the body. The brain is significantly impacted, leading to developmental delays and intellectual disability. The cardiovascular system may be affected, with some individuals having congenital heart defects, which are structural problems with the heart present from birth.
Kidney abnormalities can also occur, affecting the urinary system. Skeletal development may be altered, contributing to short stature and distinctive hand and foot features. The craniofacial region is commonly affected, resulting in the characteristic facial features often seen in individuals with this syndrome.
Risks & severity
The severity of 18p deletion syndrome can vary considerably among individuals, largely depending on the exact size and location of the deleted segment on chromosome 18. A larger deletion, or one that includes particular key genes, may lead to more significant symptoms. Developmental delays and intellectual disability are common, but their extent is variable. Some individuals may experience mild learning difficulties, while others face more substantial challenges.
Lifetime risks for specific health complications are associated with the syndrome. These can include a higher chance of certain medical conditions, such as immune system dysfunction or thyroid problems. Onset of symptoms is typically observed in infancy or early childhood, as developmental milestones are missed or physical features become apparent. While individuals with 18p deletion syndrome will require ongoing medical and developmental support, life expectancy can be normal, though it can be influenced by the presence and severity of associated medical complications, such as significant heart defects.
Genetic causes
18p deletion syndrome is caused by the loss of genetic material from the short arm of chromosome 18. This missing segment typically involves a range of genes, and the specific deleted genes contribute to the individual's symptoms. One gene located on 18p that has been studied in the context of this syndrome is *TGIF1*.
*TGIF1* encodes a protein that acts as a transcriptional repressor, meaning it helps to regulate the activity of other genes. It plays a role in cellular growth and differentiation. The *TGIF1* protein is particularly important in early embryonic development. When the *TGIF1* gene is missing as part of a larger deletion on 18p, it can contribute to some of the developmental features seen in 18p deletion syndrome, including brain and facial development [PMID:22038753]. The absence of multiple genes in the deleted region, not just *TGIF1*, collectively contributes to the complex features of the syndrome.
- TGIF1 TGFB induced factor homeobox 1
Inheritance pattern
Most cases of 18p deletion syndrome occur sporadically, meaning they are not inherited from a parent but rather arise as a new genetic change in the affected individual. This is typically due to a de novo event during the formation of reproductive cells (sperm or egg) or in early foetal development.
In rare instances, a parent may carry a balanced chromosomal rearrangement, such as a translocation, which does not cause them any symptoms but can lead to an unbalanced chromosome deletion in their children. If a parent is found to have such a rearrangement, the risk of recurrence in future pregnancies can be higher. Genetic counselling is important for families to understand the specific inheritance pattern in their situation and to discuss potential risks for future pregnancies.
Diagnosis & testing
Diagnosis of 18p deletion syndrome is typically made through genetic testing. If a healthcare professional suspects the condition based on clinical signs and symptoms, they will usually recommend a chromosomal microarray (CMA) or karyotyping. CMA is a high-resolution genetic test that can detect small missing (deletions) or extra (duplications) pieces of chromosomal material that are too small to be seen with standard karyotyping.
In the UK, genetic testing for suspected rare developmental disorders, including chromosomal conditions like 18p deletion syndrome, is typically accessed through NHS Genomic Medicine Service (GMS) pathways. Patients are usually referred by their GP, paediatrician, or another specialist to a regional clinical genetics service. Clinical geneticists and genetic counsellors help to guide the testing process and interpret the results. Relevant NHS National Genomic Test Directory R-codes would be used for such testing, which specifies the appropriate genetic analysis for different clinical presentations.
Management & lifestyle
Management for individuals with 18p deletion syndrome is multidisciplinary and focuses on addressing the specific symptoms and developmental needs of each person. There is no cure for the underlying genetic cause, so treatment aims to manage the condition's effects. Early intervention programmes, including physiotherapy, occupational therapy, and speech and language therapy, are often crucial to support development.
Regular medical surveillance is important to monitor for potential health complications such as heart defects, kidney problems, or immune system issues. This may involve routine check-ups with paediatricians, cardiologists, nephrologists, and other specialists as needed. Educational support will also be tailored to the individual's learning abilities and may involve special educational needs provision.
Families are typically supported by clinical genetics teams and genetic counsellors who provide information, support, and guidance on navigating care pathways within the NHS. They can also connect families with support groups and resources, which can be invaluable for sharing experiences and advice. Lifestyle considerations focus on creating a supportive and stimulating environment to promote the best possible developmental outcomes.
UK care pathway
In the UK, individuals suspected of having 18p deletion syndrome would typically enter the NHS Genomic Medicine Service (GMS) pathway. Referral to a regional Clinical Genetics Service is usually initiated by a GP, paediatrician, or other specialist. These services provide expert assessment, genetic counselling, and access to genomic testing, which is guided by the NHS National Genomic Test Directory. Genetic counsellors play a key role in explaining test results, discussing inheritance patterns, and providing psychosocial support to families.
Frequently asked questions
What caused my child's 18p deletion syndrome?
Most often, 18p deletion syndrome occurs sporadically, meaning it's a new genetic change in the child and not inherited from either parent. This 'de novo' event happens by chance during the formation of reproductive cells or in early development.
Will having another child with 18p deletion syndrome be a risk?
For most families where the deletion is de novo, the risk of having another child with 18p deletion syndrome is generally very low. However, genetic counselling can assess your specific situation and discuss any potential recurrence risks if a parental chromosomal rearrangement is identified.
What kind of support is available for individuals with 18p deletion syndrome?
Support typically involves a team of healthcare professionals. This includes paediatricians, geneticists, and therapists for developmental support (physiotherapy, occupational therapy, speech and language therapy). Educational support and social services are also important for managing daily living and learning.
How is 18p deletion syndrome diagnosed?
Diagnosis is made through genetic testing, usually a chromosomal microarray (CMA) or karyotyping. These tests can detect the missing segment of chromosome 18. Your doctor will refer you to a clinical genetics service for these tests.
What are the long-term prospects for someone with 18p deletion syndrome?
The long-term outlook varies widely depending on the severity of symptoms. Many individuals will experience developmental delays and intellectual disability, but with appropriate medical care, therapies, and support, they can lead fulfilling lives. Life expectancy can be normal, but may be affected by any severe associated medical conditions.
References
- Turleau C. Monosomy 18p. Orphanet journal of rare diseases. 2008. PMID: 18284672
- Hasi-Zogaj M, Sebold C, Heard P. A review of 18p deletions. American journal of medical genetics. Part C, Seminars in medical genetics. 2015. PMID: 26250845
- Balog J, Goossens R, Lemmers RJLF. Monosomy 18p is a risk factor for facioscapulohumeral dystrophy. Journal of medical genetics. 2018. PMID: 29563141
- Oktay MA, Tunca Küçükali ET, Kılınç Uğurlu A. 18p Deletion Syndrome Associated with Type 1 Diabetes and Hashimoto's Thyroiditis: A Case Report on Autoimmune Disorders and Genetic Factors. Journal of clinical research in pediatric endocrinology. 2025. PMID: 41194499
- Herlin MK, Bernth Jensen JM, Andreasen L. Monozygotic triplets with juvenile-onset autoimmunity and 18p microdeletion involving PTPRM. Frontiers in genetics. 2024. PMID: 39359478
- Grosso S, Pucci L, Di Bartolo RM. Chromosome 18 aberrations and epilepsy: a review. American journal of medical genetics. Part A. 2005. PMID: 15690352
- Crosiers D, Blaumeiser B, Van Goethem G. Spectrum of Movement Disorders in 18p Deletion Syndrome. Movement disorders clinical practice. 2019. PMID: 30746419
- Xu LJ, Wu LX, Yuan Q. A case of 18p deletion syndrome after blepharoplasty. International medical case reports journal. 2017. PMID: 28138267