Karyotype and chromosome microarray

At a glance

• A karyotype looks at whole chromosomes down a microscope. It sees number and structure, including balanced rearrangements, but nothing smaller than about 5 to 10 Mb.
• A chromosome microarray (CMA) measures copy number across the genome from DNA. It finds gains and losses down to 50 to 200 kb, but can't see balanced rearrangements or show where extra material sits.
• CMA became the first-tier test for developmental delay, intellectual disability, autism and multiple congenital anomalies (Miller 2010). ACMG now recommends exome or genome sequencing be considered first- or second-tier for these children (Manickam 2021). In Australia CMA (item 73292) is still the usual first test, with Medicare-funded exome or genome for eligible children (items 73358 to 73360).