CS Type I, the classic form, is characterized by normal fetal growth with the onset of abnormalities in the first two years of life. Impairment of vision, hearing, and the central and peripheral nervous systems progressively degenerate until death in the first or second decade of life.
CS Type II, otherwise known as connatal CS, 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. COFS syndrome can be further subdivided into several conditions (COFS types 1, 2, 3 (associated with xeroderma pigmentosum) and 4).
CS Type III, characterized by late onset, is rare and milder than Types I and II.
Xeroderma pigmentosum-Cockayne syndrome (XP-CS) occurs when an individual also suffers from xeroderma pigmentosum, another DNA repair disease. Some symptoms of each disease are expressed.
Mutations in the ERCC6 and ERCC8 genes are the cause of Cockayne syndrome. The proteins made by these genes are involved in repairing damagedDNA via the transcription-coupled repair mechanism, particularly the DNA in active genes. If either the ERCC6 or the ERCC8 gene is altered, DNA damage is not repaired. As this damage accumulates, it can lead to malfunctioning cells or cell death.
Mutations in the ERCC6 gene mutation makes up ~70% of cases.