Overgrowth Syndromes

Overgrowth syndromes are a group of genetically determined conditions of excessive somatic growth. Growth is either generalised, affecting overall body size, or segmental and asymmetric, affecting specific body regions or one side of the body disproportionately.

Beckwith-Wiedemann syndrome is the commonest and most extensively characterised. Related conditions include Sotos syndrome and hemihyperplasia, which may be isolated or part of a broader syndromic overgrowth pattern.

The shared clinical significance is an increased risk of embryonal tumours, particularly Wilms tumour and hepatoblastoma, in a proportion of affected individuals. This warrants structured, proactive tumour surveillance according to the condition and its risk profile.

Classification and pathophysiology

• Beckwith-Wiedemann syndrome results from molecular abnormalities of imprinted genes in the chromosome 11p15.5 region. These include methylation abnormalities, uniparental disomy and, in a smaller proportion, point mutations.
• The underlying molecular mechanism bears on the pattern and magnitude of tumour risk in the individual child.
• Sotos syndrome results from mutations in the NSD1 gene. It produces generalised overgrowth with distinctive facial features and frequently developmental delay. It is genetically and clinically distinct from Beckwith-Wiedemann syndrome despite some overlapping overgrowth features.
• Hemihyperplasia is asymmetric overgrowth of one side of the body or a body segment. It may occur as an isolated finding or as a component of a broader overgrowth syndrome.
• Isolated hemihyperplasia carries a recognised increased risk of embryonal tumour, somewhat lower than in Beckwith-Wiedemann syndrome. It warrants its own structured surveillance.

• Beckwith-Wiedemann syndrome presents with a characteristic constellation: macrosomia (prenatal and postnatal), abdominal wall defects (including omphalocele or umbilical hernia), organomegaly (including hepatomegaly), and characteristic ear creases or pits. Hemihyperplasia occurs in a proportion of affected individuals.
• Macroglossia is a particularly characteristic, often prominent feature. It sometimes needs surgical management because of its potential impact on feeding, speech and dental development.
• Neonatal hypoglycaemia reflects associated hyperinsulinism and is common in the neonatal period. It needs proactive monitoring and management, given the risk of neurological injury if inadequately identified and treated.
• Sotos syndrome presents with prenatal and postnatal overgrowth, particularly of height and head circumference. Characteristic facial features include a prominent forehead, sparse frontotemporal hair and a long, narrow face. A substantial proportion have developmental delay and learning difficulty of variable severity.
• Hemihyperplasia presents with visible or measurable asymmetry between the two sides of the body or between corresponding limbs, ranging from subtle to substantial.
• Careful assessment is essential to distinguish isolated, otherwise benign hemihyperplasia from hemihyperplasia that is a component of a broader syndromic overgrowth condition.
• The shared, critical clinical significance is the substantially increased risk of embryonal tumours, particularly Wilms tumour (a renal malignancy) and hepatoblastoma. The magnitude of risk varies with the underlying condition and, for Beckwith-Wiedemann syndrome, the molecular subtype.

• Diagnosis of Beckwith-Wiedemann syndrome combines characteristic clinical features with molecular genetic testing. Testing identifies the underlying abnormality in the chromosome 11p15.5 region.
• The molecular subtype bears directly on the individual's tumour risk profile and therefore on the intensity of surveillance.
• Sotos syndrome diagnosis is supported by the characteristic clinical phenotype with genetic testing for NSD1 mutations, which gives definitive molecular confirmation.
• Across the group, clinical assessment is essential. Measure and document any asymmetry carefully, and assess for the broader characteristic features of the suspected syndrome.
• Genetic counselling addresses the inheritance pattern for the particular condition and molecular subtype. Beckwith-Wiedemann syndrome shows a complex, variable pattern of inheritance and recurrence risk according to the underlying molecular mechanism.
• This supports informed family counselling about recurrence risk in future pregnancies.

• Structured tumour surveillance is the single most important component of ongoing management for conditions in this group with an elevated embryonal tumour risk.
• It comprises regular abdominal ultrasound, screening for Wilms tumour and hepatoblastoma, at structured intervals through the period of highest risk, generally early childhood. Duration and frequency depend on the underlying condition and, for Beckwith-Wiedemann syndrome, molecular subtype.
• Some protocols add periodic serum alpha-fetoprotein measurement as a surveillance marker for hepatoblastoma specifically.
• In Beckwith-Wiedemann syndrome, neonatal hypoglycaemia needs structured monitoring and prompt treatment by the general principles of neonatal hypoglycaemia management. Adequate treatment is directly relevant to avoiding neurological injury in this higher-risk population.
• Macroglossia in Beckwith-Wiedemann syndrome may need surgical tongue reduction by an experienced specialist surgical team where it impacts feeding, speech development, dental occlusion or airway function. Timing and indication are individualised to the severity and functional impact in the individual child.
• Any embryonal tumour detected through surveillance is managed by the principles for the relevant condition (Wilms tumour and hepatoblastoma). Outcome is generally more favourable when tumours are detected early through surveillance than after symptomatic presentation, which underscores the value of surveillance.
• Long-term management of this diverse but mechanistically related group is coordinated and multidisciplinary. It involves clinical genetics, paediatric oncology (for the surveillance programme) and, where relevant, additional specialists for any structural anomaly or developmental need. Family education and genetic counselling are included.