Monosomy 22q13.3

Monosomy 22q13.3 syndrome (deletion 22q13.3 syndrome or Phelan-McDermid syndrome) is a chromosome microdeletion syndrome characterized by neonatal hypotonia, global developmental delay, normal to accelerated growth, absent to severely delayed speech, and minor dysmorphic features.

Epidemiology

Due to lack of clinical recognition and often insufficient laboratory testing, the syndrome is underdiagnosed and its true incidence remains unknown.

Clinical description

The deletion occurs with equal frequency in males and females and has been reported in mosaic and non-mosaic forms. Common physical traits include long eye lashes, large or unusual ears, relatively large hands, dysplastic toenails, full brow, dolicocephaly, full cheeks, bulbous nose, and pointed chin. Behavior is autistic-like with decreased perception of pain and habitual chewing or mouthing.

Etiology

The loss of 22q13.3 can result from a simple deletion, translocation, ring chromosome formation or, less commonly, from structural changes affecting the long arm of chromosome 22, specifically the region containing the SHANK3 gene.

Diagnostic methods

The diagnosis of monosomy 22q13.3 syndrome should be considered in all cases of hypotonia of unknown etiology and in individuals with absent speech. Although the deletion can sometimes be detected by high resolution chromosome analysis, fluorescence in situ hybridization (FISH) or array comparative genomic hybridization (CGH) is recommended for confirmation.

Differential diagnosis

Differential diagnosis includes syndromes associated with hypotonia, developmental delay, speech delay and/or autistic-like behavior (Prader-Willi, Angelman, Williams, Smith-Magenis, Fragile X, Sotos, FG, trichorhinophalangeal and velocardiofacial syndromes, autism spectrum disorders and cerebral palsy; see these terms).

Antenatal diagnosis

Prenatal diagnosis should be offered for future pregnancies in families with inherited rearrangements.

Genetic counseling

Genetic counseling is recommended and laboratory studies of the parents should be considered to identify cryptic rearrangements and detect parental mosaicism.

Management and treatment

ndividuals with monosomy 22q13.3 should have routine examinations by the primary care physician, as well as genetic evaluations with referral to specialists if neurological, gastrointestinal, renal, or other systemic problems are suspected. Affected individuals benefit from early intervention programs, intense occupational and communication therapies, adaptive exercise and sport programs, and other therapies to strengthen their muscles and increase their communication skills.

Prognosis

No apparent life-threatening organic abnormalities accompany the diagnosis of monosomy 22q 13.3.