15q13.3 microdeletion

Overview

15q13.3 microdeletion occurs when a small segment of chromosome 15 is missing. This region, located at position 13.3 on the long arm of chromosome 15, contains genes that contribute to brain development and function. The deletion removes genetic material from this specific chromosomal location.

The condition shows considerable variability in how it affects individuals. Some people with this chromosomal change have learning disabilities, epilepsy, or behavioural differences, whilst others with the same deletion show no obvious features and may only be identified when testing is performed for other reasons. This variability makes it challenging to predict outcomes based on genetic testing alone. The condition is rare, though precise prevalence figures are uncertain, as mildly affected or unaffected individuals may never undergo genetic testing.

Symptoms & clinical features

Developmental and learning difficulties represent the most commonly recognised features. Many individuals experience delayed speech and language development, with some requiring speech therapy support. Learning disabilities range from mild to moderate, affecting academic progress and daily living skills. Attention deficit hyperactivity disorder (ADHD) and autism spectrum features occur more frequently than in the general population.

Seizures affect a substantial proportion of individuals with 15q13.3 microdeletion. These typically begin in childhood or adolescence and may take various forms. Some people experience absence seizures, whilst others have tonic-clonic seizures. Physical features are generally subtle and may include minor facial differences or slight variations in head size. Psychiatric conditions, including anxiety, mood disorders, and schizophrenia, have been reported in some affected adults, though the precise risk increase remains under investigation.

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Affected organs

The brain is the primary organ system affected by 15q13.3 microdeletion. The missing genetic material appears to influence early brain development, particularly affecting regions involved in learning, memory, and emotional regulation. This manifests as the cognitive, behavioural, and neurological features seen in affected individuals.

Other organ systems are typically not significantly affected, distinguishing this condition from some other microdeletion syndromes that cause multiple physical abnormalities. Most individuals have normal heart structure, kidney function, and other organ development, though comprehensive medical assessment is appropriate when the deletion is first identified.

Multiple body systems

Systemic involvement

Cellular impact

Mechanism at cellular level

Risks & severity

The clinical impact of 15q13.3 microdeletion varies substantially. Many individuals with this deletion have significant developmental or neurological features, though some show minimal or no obvious clinical signs. Inheritance studies have found that some parents carrying the same deletion show minimal or no obvious features, indicating incomplete penetrance - meaning not everyone with the deletion develops clinical problems.

For those who do develop features, the degree of learning difficulty generally falls in the mild to moderate range, with most individuals acquiring functional communication and daily living skills with appropriate support. Epilepsy, when present, often responds to standard anti-seizure medications, though management should be individualised. The risk of psychiatric conditions may increase in adolescence and adulthood, warranting ongoing monitoring and access to mental health support when needed.

Genetic causes

15q13.3 microdeletion arises from the loss of genetic material from a specific region of chromosome 15. This deletion typically occurs because of errors during the formation of egg or sperm cells, involving a process called non-allelic homologous recombination. Repetitive DNA sequences flanking the 15q13.3 region can misalign during cell division, leading to deletion of the intervening segment.

The deleted region contains genes involved in brain development and function, with ongoing research investigating how their loss contributes to clinical features. Understanding the precise mechanisms linking this deletion to specific clinical outcomes remains an active area of investigation in clinical genetics.

Inheritance pattern

Most cases of 15q13.3 microdeletion occur as new (de novo) events, meaning the chromosomal change arose spontaneously and was not inherited from either parent. In these situations, parents typically have normal chromosomes and the recurrence risk for future children is very low, though slightly higher than the general population risk.

However, the deletion can be inherited from a parent who carries the same chromosomal change. When a parent has the microdeletion, each child has a 50% chance of inheriting it. Because of variable expressivity, an affected parent may have mild features whilst their child could be more significantly affected, or vice versa. Genetic counselling is important for families to understand inheritance patterns and recurrence risks in their specific situation.

Diagnosis & testing

15q13.3 microdeletion is identified through chromosomal microarray analysis, a genetic test that examines the entire genome for missing or extra chromosomal segments. This test may be arranged when a child shows developmental delay, learning disabilities, epilepsy, or autism spectrum features. It is often performed as part of a standard genetic investigation pathway for unexplained neurodevelopmental conditions.

Testing may also identify the deletion incidentally when microarray analysis is performed for other clinical indications, or during prenatal testing. When a deletion is found, parental testing is typically recommended to determine whether it is inherited or de novo, which helps inform recurrence risk counselling. Within the NHS, referral to clinical genetics services follows standard pathways for children with developmental concerns, with paediatricians or child development teams typically initiating the referral process.

Management & lifestyle

Management focuses on addressing individual needs through educational support, behavioural interventions, and medical treatment where required. Children with learning difficulties benefit from early intervention services, including speech and language therapy, occupational therapy, and tailored educational programmes. Schools can provide additional learning support and individualised education plans.

For individuals who develop epilepsy, referral to paediatric or adult neurology services enables appropriate seizure management. Anti-seizure medications are selected based on seizure type and individual response. Regular developmental and behavioural monitoring helps identify emerging needs, with access to child and adolescent mental health services (CAMHS) when psychiatric symptoms develop. Families benefit from genetic counselling to understand inheritance, recurrence risks, and implications for other family members.

UK care pathway

Within the NHS Genomic Medicine Service, 15q13.3 microdeletion is typically identified through chromosomal microarray testing arranged by paediatric or clinical genetics services. Following diagnosis, families are offered genetic counselling to discuss the implications of the findings, including variable expressivity and recurrence risks. Ongoing care involves coordination between multiple specialists, depending on individual needs - this may include paediatrics, neurology, developmental paediatrics, and educational psychology.

Genetic counsellors provide essential support in helping families understand the uncertain prognosis associated with this microdeletion, particularly when it is identified prenatally or in a mildly affected parent. They can discuss reproductive options for future pregnancies and facilitate appropriate family member testing when indicated. NHS regional genetics services offer long-term follow-up and serve as a resource for questions that arise as children grow and develop.

Related conditions

Several other chromosomal microdeletions share overlapping features with 15q13.3 microdeletion, particularly affecting neurodevelopment and learning. The 16p11.2 deletion, for instance, also causes developmental delay, autism spectrum features, and epilepsy in some affected individuals. Similarly, 22q11.2 deletion syndrome can present with learning difficulties and psychiatric features, though it typically includes additional physical features not seen with 15q13.3 deletion.

Differentiating between these conditions relies on chromosomal microarray analysis, which precisely identifies which chromosomal segment is deleted. Understanding the specific genetic cause helps predict likely features and connects families with appropriate support networks. Some features of 15q13.3 microdeletion, particularly epilepsy and developmental delay, overlap with numerous other genetic and non-genetic conditions, highlighting the importance of comprehensive genetic evaluation in reaching an accurate diagnosis.

Frequently asked questions

References

1. Paprocka J, Coppola A, Cuccurullo C. Epilepsy, EEG and chromosomal rearrangements. Epilepsia open. 2024. PMID: 38837855
2. Varghese M, Keshav N, Jacot-Descombes S. Autism spectrum disorder: neuropathology and animal models. Acta neuropathologica. 2017. PMID: 28584888
3. Lowther C, Costain G, Stavropoulos DJ. Delineating the 15q13.3 microdeletion phenotype: a case series and comprehensive review of the literature. Genetics in medicine : official journal of the American College of Medical Genetics. 2015. PMID: 25077648
4. Unda BK, Chalil L, Yoon S. Impaired OTUD7A-dependent Ankyrin regulation mediates neuronal dysfunction in mouse and human models of the 15q13.3 microdeletion syndrome. Molecular psychiatry. 2023. PMID: 36604605
5. Hassfurther A, Komini E, Fischer J. Clinical and Genetic Heterogeneity of the 15q13.3 Microdeletion Syndrome. Molecular syndromology. 2016. PMID: 26997942
6. Zhang S, Zhang X, Purmann C. Network Effects of the 15q13.3 Microdeletion on the Transcriptome and Epigenome in Human-Induced Neurons. Biological psychiatry. 2021. PMID: 32919612
7. Prasun P, Hankerd M, Kristofice M. Compound heterozygous microdeletion of chromosome 15q13.3 region in a child with hypotonia, impaired vision, and global developmental delay. American journal of medical genetics. Part A. 2014. PMID: 24700535
8. Giovanoli S, Werge TM, Mortensen PB. Interactive effects between hemizygous 15q13.3 microdeletion and peripubertal stress on adult behavioral functions. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology. 2019. PMID: 30188511