Page 30 - Let them speak Towards a patient reported outcome measure set for

Chapter 2
Introduction
Intellectual disability (ID) occurs in 1–3% of the population and is
characterized by substantial limitations in both intellectual functioning
and adaptive behavior, originating during the developmental
period.1–3 Exogenous factors such as an infection and birth complications
may cause ID,4 and with novel techniques such as exome and genome
sequencing, a genetic etiology can be identified in up to 50% of the
individuals with ID with many more awaiting diagnosis5,6 (Figure 1). Although
these genetic neurodevelopmental disorders (GNDs), including syndromic
ID and neurometabolic disorders, are individually rare, collectively they are
common.7,8 In GNDs, the level of intellectual functioning is variable, ranging
from normal or borderline functioning to profound ID.9–11 Although GNDs
and ID populations have often been separately studied, there is substantial
overlap in patient populations.
(a)
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