Genetic testing of aetiology of intellectual disability in a dedicated physical healthcare outpatient clinic for adults with intellectual disability

Background: No guidelines exist for assessment of aetiology of intellectual disability in adults with intellectual disability by adult physicians, although robust guidelines exist for paediatric populations. It was speculated that the paediatric guidelines would also be suitable for adults.

Aims: In rural/regional setting with limited clinical genetics, to perform a quality assurance evaluation on genetics assessment of aetiology of developmental disability in adults attending a dedicated healthcare clinic for adults with intellectual disability, compared results with paediatric standards, speculates if these seem appropriate for adults and speculates on a role for clinical genetics services.

Methods: Retrospective chart audit of eligible patients looking at genetic clinical assessment, tests selected (molecular karyotype, G banding, metabolics), and yields of positive results. The results were compared with the recommended paediatric guidelines.

Results: Of 117 eligible adult patients, ideal genetic history was incomplete for 40% of patients without Down syndrome because of physician cause and lack of information. The number of abnormal genetic results increased from 46% to 66%, mainly from the molecular karyotype, though not all may have been clinically relevant. The improved yield from this test was similar to that in paediatric studies. Use of G banding and metabolic testing could be refined.

Conclusion: Improvement can be made in clinical genetic assessment, but results generally support use of molecular karyotyping as first tier testing of cause of unknown intellectual disability in adults, as in the case for paediatric populations. The study highlights a necessary complementary role for clinical geneticists to interpret abnormal results.