Chromosome 18p Tetrasomy; Isochromosome 18p; Chromosome 18 Tetrasomy 18p; Tetrasomy Short Arm of Chromosome 18; 18p Isochromosome; 18p Tetrasomy

Tetrasomy 18p is a chromosomal disorder that occurs when the short arm of chromosome 18 (18p) appears four times (tetrasomy) rather than the normal two times in cells of the body. This condition usually causes feeding difficulties in infancy, delayed development, intellectual disability that is often mild to moderate but can be severe, changes in muscle tone, distinctive facial features, and other birth defects. The signs and symptoms vary among affected individuals, and may include seizures, recurrent ear infections, mild to moderate hearing loss, gastrointestinal problems, and growth hormone deficiency.

The prognosis for persons with Tetrasomy 18p varies depending on the involved body system. However, degrees of cognitive impairment or intellectual disability are life-long. Psychiatric conditions, such as attention deficit hyperactivity disorder (ADHD) and anxiety, as well as social and behavioral challenges have also been reported.

Tetrasomy 18p is a rare disorder, known to affect about 250 families worldwide. It is usually not inherited, as most affected individuals have no history of the disorder in their family.

Diagnostic testing: The diagnosis of Tetrasomy 18p is made by physical examination and routine chromosome analysis from a blood sample, such as fluorescence in situ hybridization (FISH), and microarray analysis.

Physical findings: Children with Tetrasomy 18p may have:

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  Distinctive physical features;

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  Microcephaly;

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  Strabismus;

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  Scoliosis or kyphosis;

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  Hypotonia or hypertonia;

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  Spasticity; and

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  Birth defects affecting the heart and other organs.

Males with Tetrasomy 18p may be born with undescended testes (cryptorchidism) or hypospadias.

ICD-9: 758.89

Onset is congenital.

Treatment of Tetrasomy 18p is symptomatic and supportive and requires ongoing routine care by a multidisciplinary team specializing in the care of children and adults with multiple system involvement. The treatment depends upon the clinical features present and may include evaluations by ophthalmology, otolaryngology and audiology, cardiology, orthopedics, neurology, endocrinology, and gastroenterology. Children may also benefit from referral for developmental services and specific medical treatment for congenital anomalies.

SUGGESTED PROGRAMMATIC ASSESSMENT*

Suggested MER for Evaluation:

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  Clinical history and examination that describes the diagnostic features of the impairment;

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  Genetic testing;

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  Blood testing; and

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  Developmental assessment or psychological testing to address allegations of mental impairment may be warranted.

Suggested Listings for Evaluation:

REMARKS

Listing-level severity must be documented and evaluated under the most affected body systems.