Inverted Duplication of Chromosome 15

inv dup(15)

dic(15;15)

psu dic(15;15)

iso(15p)

Epidemiology and Etiology:

• Archaic misnomer
• 40% of all marker chromosomes
• Two copies of 15p
• Dicentric
• Not necessarily isodicentric
• One of the centromeres may be suppressed
• With or without variable amounts of 15q
• Absence of 15q duplication:
• Normal phenotype
• Presence of Prader-Willi / Angelman syndrome regions (15q11.2) on the marker:
• De novo usually
• If maternally derived (most):
1. mental retardation
2. decreased motor coordination
3. autism spectrum disorder
4. mild to no dysmorphic features
• if paternally derived (rare):
1. normal phenotype (few exceptions)
• possible mechanism of formation:
• U-loop (like isochromosomes)

Common sites:

Gross features:

Histologic features:

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Molecular features:

Other features:

• Phenotype:
• Monocentric appearance:
• Usually (perhaps always) of no harm
• Two distinct centromeres with visible intervening chromatin
• Phenotypic defect
• Presence of PWS/AS region:
• Moderate to severe mental retardation
• Epilepsy maybe
• Autistic behavior
• Mild physical defects
• risk of UPD 15
• de novo: ~5%
• depending on whether the maternally or paternally-derived chromosome is present:
• Prader-Willi syndrome, OR
• Angelman syndrome

References:

• Gersen SL, Keagle MB, eds. The Principles of Cytogenetics (2005)
• Gardner RJM, Sutherland GR. Chromosome Abnormalities and Genetic Counseling. 2nd ed. Oxford University Press, USA; 1996.