In situ hybridization probes - Molecular cytogenetics - Phelan McDermid syndrome
PhelanMcDermid Syndrome (PMS) also known as 22q13 deletion syndrome is a rare genetic syndrome caused by the absence of the SHANK3/ProSAP2 gene on the terminal end of chromosome 22, a mutation in the SHANK3 gene or a ring chromosome 22.
The most common form of PMS is caused by a de novo chromosomal deletion but one of the parents may also be a carrier.
The diagnosis is confirmed by a deletion of the 13.3 locus on chromosome 22. As the standard karyotype does not reveal microdeletions, it is important for the geneticist to specify the areas of deletion to look for. Fluorescent in situ hybridization is often necessary to confirm the presence of this deletion.
The cause of PMS has been isolated to the loss of function of a copy of SHANK3, which codes for a master scaffold protein found in the postsynaptic density of excitatory synapses. Reduced expression of SH3 and multiple repeating domains of ankyrin 3 (SHANK3) leads to a reduction in the number of dendrites and an alteration in synaptic transmission and plasticity.
