Skip to
  1. Homepage
  2. Rare diseases
  3. Search
Simple search

Simple search

(*) mandatory field


Other search option(s)

Monosomy 18p

Synonym(s) 18p- syndrome
De Grouchy syndrome
Prevalence 1-9 / 100 000
Inheritance Not applicable
or Unknown
Age of onset Neonatal
  • Q93.5
  • C0432442
MeSH -
MedDRA -


Disease definition

Monosomy 18p refers to a chromosomal disorder resulting from the deletion of all or part of the short arm of chromosome 18.


The incidence is estimated to be about 1:50,000 live-born infants.

Clinical description

In the commonest form of the disorder, the dysmorphic syndrome is very moderate and non-specific. The main clinical features are short stature, round face with short philtrum, palpebral ptosis and large ears with detached pinnae. Intellectual deficiency is mild to moderate. A small subset of patients, about 10 to 15 percent of cases, present with severe brain/facial malformations evocative of holoprosencephaly spectrum disorders.


In two-thirds of the cases, the 18p- syndrome is due to a mere terminal deletion occurring de novo. In the remaining cases the following are possible: a de novo translocation with loss of 18p, missegregation of a parental translocation or inversion, or a ring chr18. Parental transmission of the 18p- syndrome has been reported.

Diagnostic methods

Cytogenetic analysis is necessary to make a definite diagnosis.

Differential diagnosis

Differential diagnosis may include a wide number of syndromes with short stature and mild intellectual deficiency. In young children, deletion 18p syndrome may be vaguely evocative of either Turner syndrome or trisomy 21 (see these terms).

Antenatal diagnosis

Deletion 18p can be detected prenatally by amniocentesis or chorionic villus sampling and cytogenetic testing.

Genetic counseling

Recurrence risk for siblings is low for de novo deletions and translocations, but is significant if a parental rearrangement is present.

Management and treatment

No specific treatment exists but speech therapy and early educational programs may help to improve the performances of the children.


Except for the patients with severe brain malformations, the life expectancy does not seem significantly reduced.

Expert reviewer(s)

  • Dr Catherine TURLEAU

(*) Required fields.

Attention: Only comments seeking to improve the quality and accuracy of information on the Orphanet website are accepted. For all other comments, please send your remarks via contact us. Only comments written in English can be processed.

Captcha image

Detailed information

Review article
Article for general public
Get Acrobat Reader
The documents contained in this web site are presented for information purposes only. The material is in no way intended to replace professional medical care by a qualified specialist and should not be used as a basis for diagnosis or treatment.