Which Children with Motor Speech Disorders Should Be Prioritised for Genetic Testing?

A landmark clinical study has finally answered a question families have been asking for years.

More Common Than You Might Think — And More Complex

Speech difficulties are one of the most frequent concerns that bring children to paediatricians and primary care clinics. Around 5% of all children experience some form of speech sound disorder — articulation problems, phonological delays, or unclear pronunciation. For most of them, the outlook is reassuring: these conditions are highly treatable, and the majority resolve naturally by age seven, with or without speech therapy.

But within that group, there is a smaller and far more challenging subset.

Some children don’t get better. Their speech remains inconsistent, difficult to understand, and resistant to conventional therapy — often well into adolescence or adulthood. These children are estimated to represent approximately 1 in 1,000 in the general population, and they carry a diagnosis of one of two distinct motor speech disorders:

• Childhood Apraxia of Speech (CAS) — a disruption in the planning and sequencing of speech movements, implicating frontal lobe and basal ganglia pathways
• Dysarthria — a disorder of neuromuscular control and execution of speech, implicating the corticobulbar tract and the “final common” motor pathway

Both are rare. Both are severe. And for a long time, both were poorly understood in terms of their underlying causes.

Years of Searching Without Answers

For families navigating these diagnoses, one of the most painful experiences is the absence of an explanation.

Normal MRI. Normal metabolic workup. Multiple referrals across paediatrics, neurology, and rehabilitation — and still no answer to the most fundamental question: why is my child like this?

This journey — sometimes stretching over years — is what researchers call the diagnostic odyssey. It carries real costs: financial burden, psychological stress, and delayed access to targeted care.

Until recently, the genetic contribution to motor speech disorders was barely explored. In the past five years, research-based genomic studies began reporting diagnostic yields of around 30% in CAS and dysarthria cohorts — comparable to epilepsy, cerebral palsy, and intellectual disability. But those were research settings. No study had examined what happens when you apply clinical genetic testing in a real hospital clinic — until now.

The Study: Clinical Genetic Testing in a Tertiary Speech Clinic

Published in January 2026 in the European Journal of Human Genetics, a study by Van Niel, Lauretta, and colleagues from the Royal Children’s Hospital in Melbourne, Australia, filled this gap for the first time.

153 children (aged 2y 7m to 16y 5m) confirmed to have CAS or dysarthria were prospectively enrolled at a tertiary hospital speech genomics clinic. Each child was assessed by both a speech-language pathologist and a clinical geneticist, and underwent a three-part genomic workup:

• Chromosomal microarray (CMA) — to detect large copy number variants and aneuploidies
• Fragile X PCR — to screen for Fragile X syndrome
• Exome sequencing — to detect single-gene variants (trio testing with parents wherever possible)

What They Found

Nearly one in three children received a confirmed genetic diagnosis. The majority of pathogenic variants arose de novo — meaning they were not inherited from either parent, which has direct implications for recurrence counselling.

Why This Number Matters

29% is not just a statistic. It is a benchmark — and a challenge to current clinical practice.

Compare it to other neurodevelopmental conditions where genetic testing is already considered standard of care:

The numbers are virtually identical. Yet children with epilepsy or cerebral palsy are routinely offered genetic testing — while children with motor speech disorders still are not. This study calls that out as a problem. 

What Genes Are Involved?

Across the 44 children who received a diagnosis, 38 distinct genetic disorders were identified — spanning 15 genes newly implicated in CAS and dysarthria for the first time, including ADGRL1, ANK2, BPTF, CAMK2A, CUX1, FBXW7, KCND3, NSD1, RAF1, SETD2, SLC6A8, SPTBN1, SRRM2, TAB2, and TRIM8.

The implicated genes fall into three broad biological groups:

• Chromatin regulators and transcriptional modulators were the most represented group, including SETD1A, SETD2, SETD5, NSD1, and EHMT1 — all members of the SET domain methyltransferase superfamily, a protein family with an established role in post-translational regulation and neurodevelopmental disorders.

• Ion channels and solute carriers included CACNA1A, SCN8A, KCND3, SLC6A1, and SLC6A8.

• Cell signalling pathway members included FBXW7, RAF1, PPP2R5D, and TAB2.

Notably, most of the genes identified are also associated with intellectual disability, epilepsy, or autism in broader neurodevelopmental contexts — reinforcing the concept that motor speech disorders, in their monogenic forms, represent part of a wider neurodevelopmental phenotype rather than an isolated speech problem.

Who Should Be Tested First?

Not every child with a speech delay needs an exome. The practical question — and the one clinicians face every day — is: who should be prioritised?

The researchers analysed clinical variables to identify which features predicted a genetic diagnosis. The results were striking:

Delayed walking stands alone as the most powerful predictor, with an odds ratio approaching 16. A single question in the clinic — “When did your child start walking?” — can carry enormous diagnostic weight.

Also worth noting: children with both CAS and dysarthria were more likely to receive a genetic diagnosis than those with CAS alone. When both motor speech disorders co-occur, the bar for requesting testing should be lower.

Why Is ASD Associated With Lower Odds?

This counterintuitive finding deserves explanation. Among children who did not receive a genetic diagnosis, nearly half (47.7%) had ASD features or a confirmed diagnosis. The researchers interpret this as a signal that CAS in this subgroup may follow a polygenic rather than monogenic architecture — more akin to the genetic landscape of autism itself.

They propose a two-pathway model:

• Monogenic CAS: variable cognitive and motor impairment, dysmorphic features, higher diagnostic yield
• Polygenic CAS: relatively preserved cognition and motor skills, more frequent ASD features, lower diagnostic yield

This doesn’t mean children with ASD should be excluded from testing — it means the pre-test probability of finding a single causative variant is lower, and results should be interpreted accordingly.

A Note on Fragile X Testing

Zero diagnoses from Fragile X PCR in a cohort of 153 children.

This result is consistent with every prior prospective study in CAS populations, none of which has identified a Fragile X diagnosis either. The authors suggest that Fragile X testing may have limited utility as a standalone test in children presenting with motor speech disorders as the primary concern, and that its role in the standard workup panel warrants reconsideration.

---

Clinical Bottom Line: Who Needs Testing?

If a child presents with a primary motor speech disorder (CAS and/or dysarthria) alongside any of the following, clinical genomic testing should be actively considered:

✅ Delayed age of walking — the single strongest signal
✅ Receptive language impairment
✅ Borderline or mild intellectual disability
✅ Dysmorphic features
✅ Gross or fine motor delay
✅ Co-occurring CAS and dysarthria

The recommended workup is exome sequencing (trio where possible).

When ASD is the dominant co-occurring feature without other red flags, a monogenic cause is less likely — though testing remains reasonable given the overall yield.

---

A Final Word

The families of children with motor speech disorders have long carried a diagnosis without an explanation. They deserve the same diagnostic rigour we apply to epilepsy, cerebral palsy, and intellectual disability — conditions with equivalent genetic diagnostic yields that long ago made genomic testing routine.

This study is a first step toward closing that gap. It gives clinicians a clear, evidence-based framework: a checklist of features that should prompt genetic referral, and a rationale grounded in real clinical data — not just research cohorts.

Sometimes, a single genetic result can end years of uncertainty. It can tell a family why. And it can open the door to precision-based management, targeted therapies, and accurate recurrence counselling.

In a busy outpatient clinic, it starts with one question: “When did your child first walk?”

3billion provides Whole Exome Sequencing (WES) powered by automated AI reanalysis technology. If you have any questions regarding testing costs, the diagnostic process, or sample collection methods (e.g., blood or buccal swab), please leave an inquiry. Our specialized consultants will get back to you promptly.

---

Reference: Van Niel H, Lauretta M, Baker E, et al. Childhood motor speech disorders: who to prioritise for genetic testing. Eur J Hum Genet. 2026;34:639–648. DOI: 10.1038/s41431-025-01993-9

---

This article is intended for healthcare professional education and information sharing. Clinical decisions for individual patients should always be made in consultation with the treating medical team.