The X-linked FMR1 gene is associated with fragile X syndrome. Males with the condition have characteristic facial features and intellectual disability; female presentation varies and may include mood disorders. FMR1-related disorders in relatives include ataxia, tremor and early menopause.

At least 2.5% of patients with schizophrenia carry an identifiable neurodevelopmental copy number variant. This is likely to be more prevalent in patients with intellectual disability, neurodevelopmental conditions, congenital anomalies and/or a positive family history.

Hereditary multiple exostoses is one of several rare genetic conditions that can present with short stature and bony growths in childhood.

PTEN hamartoma tumour syndrome, previously known as Cowden syndrome or Bannayan-Riley-Ruvalcaba syndrome, is an autosomal dominant genetic condition that leads to an increased risk of the patient developing benign and malignant tumours. The condition may be suspected in children with macrocephaly and developmental delay, specific dermatological features, vascular features (such as arteriovenous malformations or haemangiomas) and/or gastrointestinal polyps.

Developmental delay or intellectual disability is often multifactorial in nature and, in many cases, no specific cause is identified. For some children, particularly where the level of delay is moderate, severe or profound, there will be a genomic cause.

Fragile X syndrome is the most common genetic cause of learning disability, with a prevalence of around 1 in 5,000 males. Females can also be affected, though this is less common.

Prader-Willi syndrome is a genomic imprinting disorder that typically presents neonatally with central hypotonia, poor feeding and failure to thrive. In childhood, patients typically present with hyperphagia, obesity and intellectual disability.

Autism spectrum disorders (ASDs) are typically multifactorial, with a strong genetic component influenced by environmental factors. A smaller proportion of patients will have ASD as a feature of an underlying defined genetic condition, such as fragile X or Rett syndromes.