Natural History Study for DNA Repair Disorders

Inclusion Criteria:

* Diagnosis of Cockayne syndrome (CS), xeroderma pigmentosum (XP), or trichothiodystrophy (TTD), based on genetic testing and/or key clinical characteristics l characteristics
* Has one or more of the following neurodevelopmental or neurological complications
* Gross motor delay (non-ambulatory or started walking after age 18 months)
* Language delay (non-verbal or started talking after 18 months)
* Altered muscle tone (hypertonia, dystonia, hypotonia)
* Gait difficulties, including stiff gait, short stride, frequent falls, use of orthotics, use of walker
* Tremors
* Microcephaly
* Is a family member of an individual with the above condition
* No restrictions regarding current ambulatory status
* Minimum age for enrollment eligibility will be 6 months due to fragility of neonates with severe forms of DNA repair disorders and limitations of motor assessment scales in infants younger than 6 months. There will be no maximum age for enrollment eligibility.
* No restrictions regarding gender, race, or ethnicity.
* Voluntary written consent from the participant if adult capable of consenting or parent/guardian if minor or not capable of consenting
* Written consent of Legally Authorized Representative if enrolling adult lacks capacity to consent

Exclusion Criteria:

* Any prior history of systemic gene or cell-based therapy
* Current participation in an interventional clinical trial