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