del (18q)

de Grouchy syndrome

Epidemiology and Etiology:

• Distal del(18q) more commonly encountered
• De Grouchy syndrome

Common sites:

Gross features:

• “typical 18q phenotype” – de Grouchy syndrome (18q22.3-q23)
• Characteristic facies:
• Microcephaly (18q21.33)
• Midface hypoplasia
• Hypertelorism
• Congenital aural atresia (18q22.3)
• Cleft palate / cleft lip (18q12.1-q12.3)
• Short stature (18q12.1-q12.3, 18q21.1-q21.33, 18q22.3-q23)
• Feet abnormalities

Histologic features:

•  White matter delayed myelination (18q22.3-q23)

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Molecular features:

• MBP – myelin basic protein
• Likely responsible for the myelination defects

Other features:

• Mental retardation
• Severe (deletions proximal to 18q21.31)
• Mild (deletions distal to 18q21.33)
• Hypotonia
• Strabismus (proximal 18q)
• Behavioural problems (proximal 18q)
• Growth hormone insufficiency (18q22.3-q23)

References:

• Feenstra et al. Genotype-phenotype mapping of chromosome 18q by high-resolution array-CGH: an update of the phenotypic map. Am J Med Genet A. 2007;143A:1858-1867.