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References OMIM Gene GeneReviews HGMD HGNC
last update : 4/01/2006
Symbol DEL21QD
Location 21q21.3-q22.13
Name chromosome 21q deletion, including the APP-SOD1 region
Other name(s) monosomy 21q
Corresponding gene ITSN1 , DYRK1A
Main clinical features
  • arthrogryposis-like symptoms, hypertonia, mental retardation
  • typical facial anomalies including hypertelorism, low hairline, and large nose
  • short neck, transverse palmar crease
  • severe microcephaly, a developmental delay, hypospadias, and corneal opacity in a patient who had a ~4 Mb microdeletion spanning the Down syndrome critical region, including DYRK1A and SIM2 (Fujita 2010)
  • Genetic determination chromosomal
    Related entries DEL21QT
    Function/system disorder mental retardation
    Type MCA/MR
    Gene mutationChromosome rearrangementEffectComments
      deletion haploinsufficiency deletion including the APP-SOD 1 region, grossly mirroring the "DS critical region"
      translocation haploinsufficiency most reported cases are due to familial or de novo unbalanced translocations with variable associated trisomy
    Remark(s) Several cases of presumptive monosomy 21 have been re-diagnosed using FISH as balanced or unbalanced reciprocal translocations, most often with 5p or 18q
    Genotype/Phenotype correlations deletions distal to EST2 have a different phenotype ; deletion of an 8.4-Mb region in chromosome band 21q22.2-22.3 (KCNJ6-COL6A2) is associated with cortical dysplasia (pachygyria, polymicrogyria, colpocephaly) including the DSCAM and DYRKIA genes that are expressed in brain ; the ITSN1 gene is involved in severe mental retardation in patients with 21q deletion; a critical region of 0.56 Mb containing four genes, KCNE1, DSCR1, CLIC6 and RUNX1, is associated with severe congenital heart defects; deletions of the most proximal 15-17 Mb of 21q is associated with mild or no cognitive impairment, but may lead to problems with balance and motor function.