Inclusion criteria:  Minor patient Cockayne syndrome with molecular confirmation, treated between 01/01/1985 and 01/03/2020 Collection of at least one growth data (height, weight, head circumference) for a given age Clinic compatible with type 1 or 2 Cockayne syndrome Holder of parental authority not opposing, after information, the reuse of their child's medical data for the purposes of this scientific research.  Exclusion criteria:  Refusal to participate in the study. Lack of molecular confirmation of Cockayne syndrome Lack of growth data for a given age. Clinic not compatible with type 1 or 2 Cockayne syndrome. Exclusion of type 3 Cockayne syndromes, trichothiodystrophy and xeroderma-pigmentosum.