Cockayne syndrome

Overview

Cockayne syndrome is a very rare genetic condition impacting development and leading to symptoms similar to premature ageing [PMID:31747869]. It is primarily caused by an inability of cells to adequately repair damaged DNA. This DNA repair deficiency particularly affects actively used genes, leading to a wide range of health issues.

The condition can vary in severity, but typically involves slow growth, developmental delays, and neurological challenges. Individuals with Cockayne syndrome are also highly sensitive to sunlight. The overall prevalence of Cockayne syndrome is estimated to be approximately 1 in 250,000 live births.

Symptoms & clinical features

Individuals with Cockayne syndrome generally present with a distinctive set of features. Growth failure is common, with affected children often having short stature and low weight. Significant developmental delays are typical, influencing milestones such as walking and talking. Neurological symptoms are prominent, including difficulties with coordination (ataxia), progressive loss of nerve function, and hearing or vision impairment [PMID:19307528].

Characteristic physical features may include an appearance that seems older than the child's actual age, a small head circumference (microcephaly), and sunken eyes. Sunlight sensitivity is a notable symptom; even brief exposure can cause severe sunburn and skin damage. Other symptoms can include dental problems, feeding difficulties, and stiff joints.

Video: Genetics 101

Affected organs

Cockayne syndrome can affect multiple organ systems throughout the body. The central nervous system is significantly impacted, leading to brain development issues, progressive neurological degeneration, and impaired nerve function. The eyes and ears are commonly affected, resulting in conditions like cataracts, retinal degeneration, and hearing loss.

Bone and joint health can be compromised, leading to growth problems and joint stiffness. The skin is highly vulnerable to sun damage due to the DNA repair defect. Other organs such as the liver and kidneys may also be affected in some cases, although these are less consistently observed primary features.

Brain

Central nervous system involvement

Cellular impact

Mechanism at cellular level

Risks & severity

The severity of Cockayne syndrome can vary, with some individuals experiencing more rapid progression and more significant symptoms than others. There are typically considered to be two main types: Type I (classical) and Type II (severe early-onset), with Type II often having more profound developmental issues and a shorter life expectancy. A milder Type III has also been described [PMID:19307528].

Unfortunately, Cockayne syndrome is a progressive condition. Life expectancy is significantly reduced, especially for individuals with more severe forms, with many not surviving beyond childhood or early adulthood. The exact age of onset of symptoms varies by type, but clinical signs often become apparent in early infancy or childhood. The neurological degeneration and general deterioration of organ function contribute to the progressive nature of the condition.

Genetic causes

Cockayne syndrome primarily arises from disease-causing changes (pathogenic variants) in one of two genes: ERCC6 or ERCC8. Both of these genes are vital for a process called nucleotide excision repair, which is a key mechanism cells use to fix damaged DNA [PMID:31747869]. This repair process is especially important for genes that are actively being used by the cell.

The ERCC6 gene provides instructions for making the CSB protein, while the ERCC8 gene provides instructions for the CSA protein. Both CSB and CSA proteins are essential components of the DNA repair machinery. When there are pathogenic variants in either ERCC6 or ERCC8, these proteins do not function correctly, leading to an accumulation of unrepaired DNA damage, particularly in rapidly dividing or metabolically active cells like nerve cells. This failure in DNA repair underlies the wide range of symptoms seen in Cockayne syndrome.

• ERCC6
  ERCC excision repair 6, chromatin remodeling factor
  The ERCC6 gene provides instructions for producing the Cockayne syndrome B (CSB) protein, crucial for DNA repair and accurate gene transcription.
• ERCC8
  ERCC excision repair 8, CSA ubiquitin ligase complex subunit
  The ERCC8 gene provides instructions for the Cockayne syndrome A (CSA) protein, which plays a crucial role in repairing damaged DNA, particularly within actively expressed genes.

Inheritance pattern

Cockayne syndrome follows an autosomal recessive inheritance pattern. This means that an individual must inherit two copies of a pathogenic variant - one from each parent - to develop the condition. Parents who each carry one copy of a pathogenic variant are known as carriers; they typically do not show symptoms themselves because their other unaffected gene copy can compensate.

For carrier parents, there is a 1 in 4 (25%) chance with each pregnancy that their child will inherit two pathogenic variants and therefore be affected by Cockayne syndrome. There is a 2 in 4 (50%) chance that their child will be a carrier like them, and a 1 in 4 (25%) chance that their child will inherit two unaffected copies of the gene and not be a carrier or have the condition.

Diagnosis & testing

A diagnosis of Cockayne syndrome is usually suspected based on the characteristic clinical signs and symptoms, especially the combination of developmental delay, growth failure, neurological features, and sun sensitivity. Confirmation of the diagnosis is typically achieved through genetic testing.

Genetic testing involves analysing blood or saliva samples to identify pathogenic variants in the ERCC6 or ERCC8 genes. In the UK, such testing is often accessed through the NHS Genomic Medicine Service, following referral from a paediatrician or clinical geneticist. The relevant NHS National Genomic Test Directory R-codes, such as R301 'Cockayne syndrome', would guide this testing pathway.

Management & lifestyle

Due to the complex and progressive nature of Cockayne syndrome, management focuses on alleviating symptoms, providing supportive care, and optimising quality of life. A multidisciplinary team of specialists, including paediatricians, neurologists, ophthalmologists, audiologists, dieticians, and physiotherapists, is typically involved in care.

Regular monitoring of growth, development, and neurological function is crucial. Interventions may include nutritional support for feeding difficulties, physical and occupational therapy for motor skills, special education for developmental delays, and management of vision and hearing impairments. Strict sun protection is essential due to extreme photosensitivity. Genetic counselling is also an important part of the care pathway, offering information and support to families regarding inheritance patterns and future family planning.

UK care pathway

In the UK, individuals suspected of having a rare genetic condition like Cockayne syndrome would typically enter the NHS Genomic Medicine Service pathway. This generally starts with a referral from a primary care physician or specialist (such as a paediatrician) to a regional Clinical Genetics service. Clinical geneticists and genetic counsellors are key to guiding families through diagnosis, understanding the condition, and accessing appropriate genetic testing.

Genetic counselling is available to discuss the implications of a diagnosis, including inheritance patterns and the availability of testing for family members. The NHS National Genomic Test Directory outlines the genetic tests available, with specific R-codes (e.g., R301 for Cockayne syndrome) used by clinicians to request testing.

Related conditions

When considering conditions that might have similar symptoms or shared genetic mechanisms, it is important to differentiate Cockayne syndrome from other disorders. Xeroderma Pigmentosum (XP) is another condition involving defects in DNA repair, particularly affecting nucleotide excision repair, and also causes extreme sun sensitivity and neurological problems. However, XP typically presents with a much higher risk of skin cancers at a younger age, which is not a primary feature of Cockayne syndrome.

Other conditions that might share some overlapping features, such as severe developmental delay, short stature, and microcephaly, include certain forms of mitochondrial disease or other rare neurodegenerative disorders. However, the specific combination of progressive neurological degeneration, growth failure, sun sensitivity, and premature ageing features helps to distinguish Cockayne syndrome.

• Cockayne syndrome type B
  Neurogenetics
  Shares 1 gene

Frequently asked questions

References

1. Adam MP, Bick S, Mirzaa GM. Cockayne Syndrome. 1993. PMID: 20301516
2. Nieto Moreno N, Olthof AM, Svejstrup JQ. Transcription-Coupled Nucleotide Excision Repair and the Transcriptional Response to UV-Induced DNA Damage. Annual review of biochemistry. 2023. PMID: 37040775
3. Kajitani GS, Brace L, Trevino-Villarreal JH. Neurovascular dysfunction and neuroinflammation in a Cockayne syndrome mouse model. Aging. 2021. PMID: 34628368
4. Tiwari V, Baptiste BA, Okur MN. Current and emerging roles of Cockayne syndrome group B (CSB) protein. Nucleic acids research. 2021. PMID: 33590097
5. Deger N, Yang Y, Lindsey-Boltz LA. Drosophila, which lacks canonical transcription-coupled repair proteins, performs transcription-coupled repair. The Journal of biological chemistry. 2019. PMID: 31624146
6. Dev N, Aggarwal P. Xeroderma pigmentosum-Cockayne syndrome complex. The Indian journal of medical research. 2020. PMID: 35345132
7. Spitz MA, Severac F, Obringer C. Diagnostic and severity scores for Cockayne syndrome. Orphanet journal of rare diseases. 2021. PMID: 33536051