Intellectual Disability and Learning Difficulties

Children with features of developmental delay (DD) or intellectual disability (ID) should be referred to a paediatrician for a clinical genetics evaluation. Approach the child and family with patience and understanding — DD/ID carries real risk to a person’s ability to live independently and increases vulnerability to financial, sexual, and emotional abuse.

Causes are genetic, non-genetic (e.g. fetal alcohol spectrum disorder, congenital infection), or unknown. Identifying an underlying genetic cause can inform both ongoing management and parents’ future reproductive risk.

Genetic causes:

• Chromosomal — abnormal chromosome number (e.g. Down syndrome), or a partial chromosomal deletion/duplication.
• Single-gene, de novo — a variant arising in the child, not inherited from a parent (e.g. Rett syndrome).
• Inherited — autosomal dominant (e.g. tuberous sclerosis), autosomal recessive (e.g. PKU), or X-linked recessive (e.g. Fragile X syndrome).

Assessment

Take a 3-generation family tree, and review medical history (previous diagnoses/investigations, especially genetic testing) and developmental milestones (walking, language, any regression, school literacy).

Consider the cause — any condition impairing brain development can contribute: prenatal/perinatal factors (infection in pregnancy, hypoxic birth injury), postnatal factors (infection, head injury), genetic conditions, or environmental factors (e.g. severe neglect/abuse). Many adult presentations occur without a formal childhood diagnosis — often surfacing when an elderly carer can no longer manage, or when a sibling seeks pre-conception advice.

Examine for dysmorphic features, and check head circumference and weight. Consider referral for investigation with modern genetic techniques.

Genetic testing

Chromosome microarray (CMA) is now the first-line genetic test for DD, ID, autism spectrum disorder, and congenital abnormalities. CMA doesn’t detect the FMR1 variant causing Fragile X syndrome, so order a separate FXS DNA test alongside it. GPs can order CMA, though many prefer not to given the complexity of interpretation — ordering CMA and FXS testing in parallel with a paediatric referral can reduce the patient’s overall wait time.

An MBS rebate is available for CMA where the patient has DD, ID, ASD, or ≥2 congenital abnormalities. FXS DNA testing is MBS-rebated where the patient has ID/ataxia/neurodegeneration/premature ovarian failure consistent with an FMR1 mutation, or has a relative with a known FMR1 mutation.

Management

Suspect a genetic cause, and refer to a paediatrician or genetics service, if DD is accompanied by: dysmorphic features; autistic features; epilepsy; a congenital anomaly (e.g. cleft palate, heart defect); or a family history of autism, FXS, or another developmental/learning disability.

Refer directly to a paediatric neurologist if there’s regression of motor skills (e.g. suspected muscular dystrophy or spinal muscular atrophy).

For a formal ID diagnosis, a specialised psychological assessment is needed — refer privately, or via a disability support service for patients without private access.

Before referring, clarify with the patient/family what they want from it — understanding the diagnosis/prognosis/management, or clarifying reproductive risk. All referrals need a 3-generation family tree. If the patient or a relative is in early pregnancy, request an acute genetic health assessment; otherwise, referrals are generally non-urgent.