(syndrome 21q, partial monosomy 21q)

Very rare: less than 50 cases have been described. Complete monosomy 21 is probably not compatible with life. It is usually a variable partial deletion of a segment of the long arm of chromosome 21, leading to an increased risk of congenital malformations, developmental delay and intellectual deficit: the severity of the phenotype varies according to the location and size of the deletion. Deletions can occur de novo or following parental rearrangement. Monosomy linked to a parental rearrangement mis-segregation is usually associated with another imbalance that may complicate the phenotype. Some cases arise from the formation of a ring chromosome 21.

In general, proximal and distal deletions lead to a less severe phenotype, while deletions involving band 21q22are associated with a more severe phenotype.

Severe forms :

-        intrauterine and postnatal growth retardation,

-        microcephaly with prominent occiput

-        facial dysmorphism: up- or downslanting palpebral fissures, prominent nasal bridge associated with a broad nose, and large ears.

-        severe intellectual deficit

-        sometimes stiff joints and held in an unusual position

-        muscular hypotonia

-        convulsions

-        sometimes: specific blood anomalies (thrombocytopenia, myelodysplasia).

-        malformations are often observed: cerebral (cerebral atrophy, cortical dysplasia, corpus callosum dysgenesis) and cardiac (persistent ductus arteriosus, septal defects).

Anesthetic implications:

echocardiography, risk of difficult intubation, epilepsy. Increased risk of oxygen toxicity (1 case) ?

References : 

-        Ackerman AD,  Fackler JC, Tuck-Muller CM, Tarpey MM, Freeman BA, Rogers MC.
Partial monosomy 21, diminished activity of superoxide dismutase, and pulmonary oxygen toxicity.
N Engl J Med 1988 ; 318 :1666-9.

-        Burgess T, Downie L, Pertile MD, Francis D, Glass M, Nouri S, Pszczola R.
Monosomy 21 seen in live born is unlikely to represent true Monosomy 21: a case report and review of the literature.
Case Reports in Genetics 2014, 965401 doi.org/10.1155/2014/965401

-        Saito Y, Chaki T, Nishihara N, Yamakage M.
A case of monosomy 21 presented with difficult tracheal intubation.
JA Clinical Reports 2022;  8:24 doi.org/10.1186/s40981-022-00511-w

Updated: June 2023