They also compared Cockayne syndrome to what is now known as Hutchinson–Gilford progeria syndrome (HGPS), then called progeria, due to the advanced aging that characterizes both disorders. Types
CS Type I, the "classic" form, is characterized by normal fetal growth with the onset of abnormalities in the first two years of life. Vision and hearing gradually decline. The central and peripheral nervous systems progressively degenerate until death in the first or second decade of life as a result of serious neurological degradation. Cortical atrophy is less severe in CS Type I.
CS Type II is present from birth (congenital) and is much more severe than CS Type 1. It involves very little neurological development after birth. Death usually occurs by age seven. This specific type has also been designated as cerebro-oculo-facio-skeletal (COFS) syndrome or Pena-Shokeir syndrome Type II. COFS syndrome is named so due to the effects it has on the brain, eyes, face, and skeletal system, as the disease frequently causes brain atrophy, cataracts, loss of fat in the face, and osteoporosis. COFS syndrome can be further subdivided into several conditions (COFS types 1, 2, 3 (associated with xeroderma pigmentosum) and 4). Typically patients with this early-onset form of the disorder show more severe brain damage, including reduced myelination of white matter, and more widespread calcifications, including in the cortex and basal ganglia. CS Type III, characterized by late-onset, is typically milder than Types I and II. Often patients with Type III will live into adulthood.
Each lesion—a damaged section of DNA—must be snipped out and the DNA repaired to preserve its normal function. Unrepaired DNA can lose its ability to code for proteins. Mutations also can result. These mutations can activate oncogenes or silence tumor suppressor genes. According to research, oxidative damage to active genes is not preferentially repaired, and in the most severe cases, the repair is slowed throughout the whole genome. The resulting accumulation of oxidative damage could impair the normal functions of the DNA and may even result in triggering a program of cell death (apoptosis). The children with this disease do not repair the active genes where oxidative damage occurs. Normally, oxidative damage repair is faster in the active genes (which make up less than five percent of the genome) than in inactive regions of the DNA. The resulting accumulation of oxidative damage could impair the normal functions of the DNA and may even result in triggering a program of cell death (apoptosis). Genetics
Cockayne syndrome is classified genetically as follows:
Mutations in the ERCC8 (also known as CSA) gene or the ERCC6 (also known as CSB) gene are the cause of Cockayne syndrome. Mutations in the ERCC6 gene mutation makes up ~70% of cases. The proteins made by these genes are involved in repairing damaged DNA via the  transcription-coupled repair mechanism, particularly the DNA in active genes. DNA damage is caused by ultraviolet rays from sunlight, radiation, or free radicals in the body. A normal cell can repair DNA damage before it accumulates.