The management of genetic disorders is a major part of the role of a paediatrician in developed countries. The correct diagnosis of genetic disorders, and their differentiation from sporadic or environmentally caused malformations is important in the proper care of children and their families. Diagnosis is based on a combination of biochemical abnormalities, characteristic muscle biopsy ‘ragged red fibres’, brain magnetic resonance imaging and genetic testing. Mitochondrial deoxyribonucleic acid is exclusively maternally inherited and for the purposes of genetic counselling the risk of paternal inheritance of a mitochondrial mutation is zero. While most congenital heart disease is sporadic and isolated, cardiac malformation is a frequent and diagnostically discriminating feature of some inherited genetic syndromes caused by mutation with a specific gene. Diagnosis is by characteristic clinical features and/or confirmatory molecular genetic testing. Radiographs of the hands can provide further supportive evidence, including the presence of cone-shaped epiphyses. Genetic confirmation can be provided by mutation analysis of GNAS1.