Trisomy 18p Treatment and Surveillance

(Aliases: partial trisomy 18)
ICD-10 = Q93.2

These recommendations are based primarily on the medical literature and therefore can be incomplete. It should be noted that there is a great deal of variation among individuals with Trisomy 18p. Not all complications or concerns will be listed in this document. However, the recommendations contained here should be used as a baseline for monitoring and the health of individuals with Trisomy 18p

Below that text there are four sets of numbered images showing types of chromosome configurations that might lead to Trisomy 18p. Image #1 shows two normal copies of chromosome 18 plus a third chromosome that is composed of a chromosome 18p arm attached to the long arm of another chromosome. That other chromosome might be chromosome 13, 14, 15, 21 or 22. Image #2 shows two normal copies of chromosome 18 plus an independent copy of the chromosome 18 p arm. image #3 shows one normal copy of chromosome 18 plus a second copy of chromosome 18 with a duplicated p arm attached to the top of the normal p arm, one p stacked on the end of another p that is fully properly connected to the q arm. Image #4 shows one normal copy of chromosome 18 plus a copy of chromosome 18 that is missing the p arm plus a third chromosome composed of two copies of chromosome 18p.

There are 27 cases reported in the literature. These cases did not have additional chromosomal copy number changes and were not mosaic. This included:

  • 14 males and 13 females
  • 11 were identified incidentally; not related to the person’s own developmental delay or intellectual disability.

*Not every aspect was described for every patient especially for the incidentally identified cases. Therefore the denominator may be different for different phenotypes

Potential conditions in a neonate:

  • Birth weight mean 20th percentile
  • Birth length mean 25th percentile
  • OFC mean 50th percentile
  • Neonatal complications
    • None occurred in more than single cases
  • Congenital malformations
    • Cryptorchidism in 21% of males

Immediate Referrals to:

  • Appropriate subspecialist as indicated by initial evaluations
  • Genetics follow-up if not previous to diagnosis
  • Early intervention/developmental services
  • The Chromosome 18 Registry & Research Society
  • The Chromosome 18 Clinical Research Center

Closely monitor and manage:

  • Psychomotor development
    • 1 normal, 4 slight delay, 4 delayed
  • Intellectual Development
    • 7 normal, 10 mild ID or LD, 5 moderate ID
  • Neurology
    • Seizures, childhood onset – 11%
    • Facial nerve palsy, congenital – 7%


  • Hearing loss- 11%

Adult Outcomes

  • 5 of 5 adult females had children
  • No males had children
  • 2 males had oligospermia

There is additional information on each of the areas mentioned above within the downloadable PDF document.

Updated 2020