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

Simple search

(*) mandatory field


Other search option(s)

1q21.1 microdeletion syndrome

Synonym(s) Del(1)(q21)
Monosomy 1q21.1
Prevalence Unknown
Inheritance Autosomal dominant
or Not applicable
Age of onset Infancy
  • Q93.5
MeSH -
MedDRA -


Disease definition

1q21.1 microdeletion syndrome is a newly described recurrent deletion syndrome with variable clinical manifestations but without the clinical picture of thrombocytopenia - absent radius (TAR) syndrome.


It has been described in 46 patients to date.

Clinical description

The clinical phenotype is extremely variable; the most common but non-constant clinical findings include microcephaly, developmental delay or mild intellectual deficit, slight facial dysmorphic features and eye abnormalities. Congenital malformations are not common. Autism spectrum disorders, schizophrenia or attention deficit hyperactivity disorder have been noted occasionally.


This syndrome is caused by a recurrent 1.35Mb deletion in the distal 1q21.1 region distinct from the deletion region implicated in TAR syndrome (see this term).

Diagnostic methods

This microdeletion was identified by comparative genomic hybridization (CGH) microarray and is only diagnosed by molecular cytogenetics. It cannot be identified by routine chromosome analysis.

Genetic counseling

The underlying mechanism is non-allelic homologous recombination (NAHR). Deletions appear de novo or can be inherited in an autosomal dominant manner from mildly affected or completely normal parents. This suggests that the distal 1q21.1 microdeletion has incomplete penetrance and variable expressivity.

Expert reviewer(s)


(*) 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

Summary information
Clinical genetics review
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.