exome

The exome is the part of the genome that actually codes for proteins — the collection of all the exons, the segments of genes that survive into the final messenger RNA. If the whole genome is a sprawling encyclopedia, the exome is just the sentences that get translated into action.

Although exons make up only about one to two percent of the human genome, they harbor a large share of the variants currently known to cause inherited disease. That makes sequencing the exome alone — called whole-exome sequencing — an efficient strategy: it captures the most interpretable, protein-changing region at a fraction of the cost of sequencing everything.

The limitation is precisely what it leaves out. By focusing on coding exons, exome sequencing can miss variants in regulatory regions, deep within introns, or in structural changes that span large stretches of DNA. So a 'normal' exome result does not rule out a genetic cause that lives elsewhere in the genome.