Array CGH testing

Array CGH testing is now considered to be the front line test for patients presenting with developmental delay (motor or growth), autism spectrum disorder, moderate to severe learning difficulties, dysmorphic features, with or without congenital abnormalities.

Chromosome abnormalities can be associated with developmental delay, autism spectrum disorder, learning difficulties, dysmorphic features and other congenital abnormalities.

Array CGH can detect smaller genetic changes than is possible by conventional karyotyping, and can provide accurate information on the size and possible consequences of the gains (duplications) or losses (deletions) identified. Multiple studies have shown that Array CGH, when applied to appropriate patients, will detect up to three times more pathogenic chromosome imbalances than karyotyping due to its greater precision and sensitivity.

Array CGH testing is now considered to be the front line test for patients presenting with developmental delay (motor or growth), autism spectrum disorder, moderate to severe learning difficulties, dysmorphic features, with or without congenital abnormalities. Consortiums
in the USA and many EU countries have adopted Array CGH as the front line test in this patient cohort.

Array CGH is now more frequently used for prenatal studies as an adjunct or replacement for conventional cytogenetic studies, particularly where structural fetal abnormalities are seen at ultrasound scan but also at a patient’s or doctor’s request. The technique may also be utilised as a follow up test to characterise anomalies detected by a previous study (e.g. an apparently balanced de novo rearrangement or marker chromosome).

When to use Array CGH

In postnatal cases, patients should present with one or more of the following:

• Mental retardation
• Autism/autism spectrum disorder
• Congenital malformations
• Developmental delay
• Dysmorphic features

In prenatal cases, patients may present with:

• Abnormalities or increased nuchal translucency on ultrasound scan which may be associated with a chromosome imbalance.

Approximately 10–20% of results identify extra or missing DNA which may or may not be relevant to the clinical phenotype, and will require further family studies to assist with interpretation.

What can Array CGH detect?

Deletions and duplications with greater sensitivity than conventional karyotyping.

What does Array CGH not detect?

• Balanced chromosome rearrangements such as translocations or inversions.
• The chromosome location of duplications (this would require additional FISH testing).
• Low Frequency Mosaicism (<30% abnormal cells), some types of polyploidy like triploidy, Uniparental disomy (UPD) and Fragile X syndrome, imprinting defects, genetic diseases caused by point mutations or multifactorial inheritance.

Further information is provided by the UNIQUE website.