A 400 kb duplication, 2.4 Mb triplication and 130 kb duplication of 9q34.3 in a patient with severe mental retardation

The presence of a duplication as well as a triplication in one chromosome is a rare rearrangement and not easy to distinguish with routine chromosomal analysis. Recent developments in array technologies, however, not only allow screening of the whole genome at a higher resolution, but also make it possible to characterize complex chromosomal rearrangements in more detail. Here we report a molecular cytogenetic analysis of a 16-year old female with severe mental retardation and an abnormality at the end of the long arm of chromosome 9. Subtelomeric multiplex ligation-dependent probe amplification (MLPA) analysis revealed that the extra material originated from the telomeric end of chromosome 9q. Fine mapping using a high-resolution single nucleotide polymorphism (SNP) array detected a duplication of ∼400 kb upstream of a ∼2.4 Mb triplication followed by a duplication of ∼130 kb of chromosome 9q34.3. This study underscores the value of combining conventional karyotyping with novel array technologies to unravel complex chromosomal alterations in order to study their phenotypic impact.