Table 1. Categories of structural chromosome abnormalities (SCA) and important assumptions used in the analysis.

Category	Definition	Important assumptions
Category 1: Mild forms	Mental retardation, mild degree, no anomalies	- 10% of SCA - Average age is 58 years, same as a Down syndrome patient [38]. - Requires close care by parents until the age of 22 years. - Receives developmental and special education services.
Category 2: Moderate forms	Mental retardation with minor anomalies	- 45% of SCA - Average age is 18 years. - Requires close care by parents. - Does not receive developmental and special education services.
Category 3: Severe forms1	Mental retardation with major anomalies	- 45% of SCA - Average age is 5 years. - Requires close care by parents. - Does not receive developmental and special education services.

¹Excluding spontaneous abortions and perinatal deaths