Whole exome sequencing (WES) for autism: what it finds, and what it can do for your family

What whole exome sequencing actually is

Every cell in your child’s body carries about 3 billion letters of DNA. Only a small slice of it — roughly 1 to 2 percent — actually codes for proteins, the working parts that build and run the body. That slice is the exome: about 20,000 genes.

Whole exome sequencing (WES) reads that slice in one test, looking for changes that explain a medical picture — in this case, developmental delay, intellectual disability, or autism itself. It is different from:

• Chromosomal microarray (CMA) — checks for missing or duplicated chunks of chromosomes, not individual gene changes. It has been a standard first-tier test for years, but it looks at far less of the genome than WES does.
• Fragile X testing — a specific test for a repeat-expansion mutation in one gene (FMR1). WES does not reliably catch this kind of change, so fragile X still needs its own test.
• Whole genome sequencing (WGS) — reads nearly all 3 billion letters, not just the protein-coding slice. WGS can catch a few variant types WES misses, but for autism the two currently find a cause at similar rates, and WES remains more widely available and often less expensive.

Why test: what a result can do for your child, you, and your child’s medical team

Testing cannot diagnose autism — your child already has that answer from clinical evaluation. What WES can do is find an underlying genetic condition, and a named condition is useful in three different, concrete ways.

For your child

Many of the conditions WES finds come with a screening schedule for problems that have not shown up yet — heart, kidney, vision, hearing, or seizure risk tied to a specific gene. Finding the condition early means screening starts on a schedule, before a symptom forces the issue. Occasionally, a result points toward a specific treatment rather than only a watch-and-screen plan.

For you

A named genetic cause gives you a documented medical explanation you can hand to a school team, an insurer, or a new clinician — it is evidence, not just a description of behavior. It can also change the conversation about future children: some genetic findings carry a known chance of recurrence, which is information you can bring to a genetic counselor when you are ready for that conversation, on your own timeline. And a named condition often connects you to a syndrome-specific parent community that a general autism diagnosis does not.

For your child’s medical team

A result lets your child’s doctors stop guessing. Instead of ordering tests one at a time as new questions come up, a genetics team can lay out what to check and how often, in one plan. WES can also surface a medically actionable finding unrelated to autism entirely — a heart-rhythm gene or a cancer-predisposition gene, for example — that changes what your child’s medical team watches for over their lifetime. (More on this in “Secondary findings,” below.) And once a cause is identified, your team can stop ordering duplicate diagnostic workups aimed at ruling out possibilities that have already been settled.

How WES compares to the older tests

Because WES looks at thousands of genes at once rather than the handful a panel or microarray covers, professional genetics guidelines increasingly recommend it as a first-tier test — with fragile X testing run alongside it, not replaced by it.

What WES will not do

• Diagnose autism
• Find something in every child
• Change who your child is
• Replace educational evaluation or supports
• Catch a fragile X mutation (order that test separately)

Autism is diagnosed clinically — getting assessed. A full walkthrough of the broader genetic-testing decision, including what a result can and cannot mean and how to prepare for the blood or saliva draw, is on the genetic testing, explained page.

Secondary findings: the part parents aren’t always told about

Because WES reads thousands of genes in one pass, it can turn up something unrelated to why you tested in the first place. A current professional guideline (the ACMG secondary-findings list, version 3.3, 2025) names 84 genes as “medically actionable” enough to report as a secondary finding — most tied to heart-rhythm disorders or inherited cancer risk, conditions where knowing early genuinely changes care.

This is optional, not automatic. Most labs ask, before testing begins, whether your family wants these results if something turns up. There is no wrong answer — some parents want every actionable finding; others want only what explains the reason they tested. Ask your genetics team how their lab handles this choice, and make it deliberately rather than by default.

Getting tested: trio, turnaround, and cost

Trio vs. proband-only. Testing your child alone (proband-only) is common and useful. Testing both parents alongside your child (trio) resolves more uncertain results, because genetics can see directly which variants your child inherited and which are new — and it generally finds a cause more often. Ask whether trio testing is available and covered before you decide.

Turnaround. Turnaround time varies by lab and case, and standard exome sequencing commonly takes several weeks. Expedited “rapid” exome sequencing, usually reserved for a child who is hospitalized, is faster — but one inpatient study found real-world turnaround still averaged about 18 days (range 5 to 43 days) from order to result once sample-shipping delays were counted, well short of the days-only turnaround some labs advertise.

Cost and coverage. Coverage has been expanding as more medical societies endorse exome sequencing as first-tier testing for developmental delay. Ask your clinician for a letter of medical necessity, and check your plan and your state Medicaid policy — sequencing that would have been denied a few years ago is often approved today.

Questions to ask genetics

1. Is whole exome sequencing the right first test for my child, or would a panel or microarray make more sense here?
2. Has fragile X been ordered separately?
3. Is trio testing available, and is it covered?
4. How do you handle secondary findings, and when do we decide whether we want them?
5. If the result is uncertain, what happens next — and is re-analysis planned later?
6. What would change about my child’s care, in the next year, if this comes back positive?

Write the answers in your notebook. Future clinicians will ask the same things.

Related

Genetic testing, explained · Seizures · Why autism happens · Diagnostic codes

Questions parents ask after reading this

Use these with your co-parent, teacher, or clinician so the next conversation is concrete.

1. What is the single highest-yield change we can make in the next seven days based on this page?
2. What should we stop doing that is adding load without helping?
3. Who else needs a one-page summary of this plan (school, caregiver, relative)?
4. What would “a little better” look like in two weeks so we know the plan is working?

Write the answers down. Plans that live only in your head disappear on hard days.

If you only do three things

1. Pick one action from this article and schedule it on the calendar (call, email, or routine change).
2. Tell one other adult the plan in one sentence so you are not carrying it alone.
3. Revisit this page after two weeks and note what changed — keep, adjust, or drop.

Small completed steps beat perfect unread plans. You are allowed to go slowly and still be a good parent.