Tetrasomy 18p

Editor-In-Chief: Prab R Tumpati, MD
Obesity, Sleep & Internal medicine
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Tetrasomy 18p
Diagram of an isochromosome
Synonyms	N/A
Pronounce	N/A
Specialty	N/A
Symptoms	Developmental delay, intellectual disability, hypotonia, dysmorphic features
Complications	N/A
Onset	Congenital
Duration	Lifelong
Types	N/A
Causes	Isochromosome formation of the short arm of chromosome 18
Risks	Advanced maternal age
Diagnosis	Karyotype analysis, fluorescence in situ hybridization (FISH)
Differential diagnosis	Trisomy 18, Monosomy 18p
Prevention	N/A
Treatment	Supportive care, physical therapy, speech therapy
Medication	N/A
Prognosis	Variable, depends on severity of symptoms
Frequency	Rare, estimated at 1 in 140,000 live births
Deaths	N/A

Tetrasomy 18p is a rare chromosomal disorder characterized by the presence of an extra isochromosome 18p, resulting in four copies of the short arm of chromosome 18. This condition is a type of aneuploidy, where there is an abnormal number of chromosomes in the cells of the body.

Genetics

Tetrasomy 18p occurs due to the formation of an isochromosome, which is a chromosome with identical arms. In this case, the isochromosome consists of two copies of the short arm (p arm) of chromosome 18. This results in the presence of four copies of the 18p arm in each cell, instead of the usual two. The formation of the isochromosome can occur during meiosis, the process of cell division that produces gametes, or during early embryonic development. The exact mechanism of isochromosome formation is not fully understood, but it is believed to involve errors in chromosome segregation.

Clinical Features

Individuals with tetrasomy 18p may exhibit a range of clinical features, which can vary widely in severity. Common features include:

• Developmental delay and intellectual disability
• Hypotonia (reduced muscle tone)
• Distinctive facial features, such as a high forehead, flat nasal bridge, and epicanthal folds
• Congenital heart defects
• Skeletal abnormalities, such as scoliosis or joint contractures

Diagnosis

The diagnosis of tetrasomy 18p is typically made through karyotyping, a laboratory technique that allows for the visualization of chromosomes. In individuals with tetrasomy 18p, karyotyping will reveal the presence of the extra isochromosome 18p. Fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH) are additional techniques that can be used to confirm the diagnosis and provide more detailed information about the chromosomal abnormality.

Management

There is no cure for tetrasomy 18p, and management focuses on addressing the specific symptoms and complications associated with the condition. This may involve:

• Early intervention programs to support developmental progress
• Physical and occupational therapy to improve motor skills and muscle tone
• Regular monitoring and treatment of congenital heart defects
• Surgical interventions for skeletal abnormalities, if necessary

Prognosis

The prognosis for individuals with tetrasomy 18p varies depending on the severity of the symptoms and the presence of associated medical conditions. With appropriate medical care and support, many individuals can lead fulfilling lives.

See also

• Chromosomal disorder
• Isochromosome
• Aneuploidy
• Developmental delay