• learning disability
• fragile X syndrome
• chromosome abnormality
• investigations

• LD, learning disability
• LDCU, learning disability-cause unknown

Global learning disability (LD) is a neurodevelopmental defect in the capacity to acquire all or most learned higher mental skills that has a birth incidence of between 0.6% and 8% depending on case definition.¹ LD shows extreme aetiological heterogeneity and can be the result of prenatal (most common and mostly genetic), perinatal (mostly hypoxic-ischaemic), or postnatal (mostly trauma or infective) onset disease processes. A specific diagnosis aids both accurate prognosis and genetic counselling but history and physical examination alone often cannot firmly establish the aetiology. In this situation, the consensus of expert opinion is that chromosome analysis and fragile X DNA testing be performed as minimum laboratory investigations.² We wished to assess the completeness of these basic investigations in a community based population with LD.