Tetrasomy 18p: Sixty-Second Summary

(Aliases: isochromosome 18p)

Key points on genotype

• Nearly all individuals with Tetrasomy 18p have the same genotype.
• Definitive diagnosis requires:A chromosome microarray to determine the precise region of net copy number change.
• A karyotype to demonstrate that the copy number change is due to an isochromosome.
• Almost all are de novo events as opposed to inherited from a parent.
• There have been a few case reports of parents with mosaicism or with a chromosome rearrangement.
• Parents may consider chromosome analysis to better define risks for future pregnancies.

Key Points on phenotype

• Most individuals are not medically fragile.
• Developmental delay is very common.
• The average full scale IQ score  is 48, though there is a wide range of ability.
• Behavioral concerns are common.
• Life expectancy is believed to be near normal.
• Congenital anomalies are possible. Specifically, individuals with Tetrasomy 18p have an increased likelihood of myelomeningocele, heart defects, hernias, palate abnormalities and orthopedic abnormalities.

Follow-up

• Affected individuals do not appear to be at increased risk for adverse reactions to drugs or standard medical treatments.
• Recommendations for specific evaluations  and treatments are in the following sections.

Enrollment

• The Chromosome 18 Clinical Research Center is enrolling anyone with any chromosome 18 abnormality in our longitudinal study of all aspects of the conditions.
• Parents may contact Annice Hill at hilla3@uthscsa.edu or call (210) 567-5321.
• Enrollment requires the diagnostic genetics report and any other informative medical records

Consultation

• Daniel Hale, MD, Medical Director of the Chromosome 18 Clinical Research Center can be reached through Annice Hill at hilla3@uthscsa.edu or call (210) 567-5321.

Updated 2020