a transcription dependent manner and facilitates homologous recombinational repair of the breaks. During the G0/G1 phase of the cell cycle, DNA damage can trigger a CSB-dependent recombinational repair process that uses an RNA (rather than DNA) template. The premature aging features of CS are likely due, at least in part, to the deficiencies in DNA repair (see DNA damage theory of aging). Diagnosis People with this syndrome have smaller than normal head sizes (microcephaly), are of short stature (dwarfism), their eyes appear sunken, and they have an "aged" look. They often have long limbs with joint contractures (inability to relax the muscle at a joint), a hunched back (kyphosis), and they may be very thin (cachetic), due to a loss of subcutaneous fat. Their small chin, large ears, and pointy, thin nose often give an aged appearance. The skin of those with Cockayne syndrome is also frequently affected: hyperpigmentation, varicose or spider veins (telangiectasia), and serious sensitivity to sunlight are common, even in individuals without XP-CS. Often patients with Cockayne Syndrome will severely burn or blister with very little heat exposure. The eyes of patients can be affected in various ways and eye abnormalities are common in CS. Cataracts and cloudiness of the cornea (corneal opacity) are common. The loss of and damage to the nerves of the optic nerve, causing optic atrophy, can occur. Nystagmus, or involuntary eye movement, and pupils that fail to dilate demonstrate a loss of control of voluntary and involuntary muscle movement. A salt and pepper retinal pigmentation is also a typical sign. Diagnosis is determined by a specific test for DNA repair, which measures the recovery of RNA after exposure to UV radiation. Despite being associated with genes involved in nucleotide excision repair (NER), unlike xeroderma pigmentosum, CS is not associated with an increased risk of cancer. Laboratory Studies In Cockayne syndrome patients, UV-irradiated cells show decreased DNA and RNA synthesis. https://emedicine.medscape.com/article/1115866-workup#c5 Laboratory studies are mainly useful to eliminate other disorders. For example, skeletal radiography, endocrinologic tests, and chromosomal breakage studies can help in excluding disorders included in the differential diagnosis. Imaging Studies Brain CT scanning in Cockayne syndrome patients may reveal calcifications and cortical atrophy. Other Tests Prenatal evaluation is possible. Amniotic fluid cell culturing is used to demonstrate that fetal cells are deficient in RNA synthesis after UV irradiation. Neurology Imaging studies reveal a widespread absence of the myelin sheaths of the