Health condition
RASopathies
The RASopathies - Noonan syndrome and its relatives (cardiofaciocutaneous, Costello, Noonan with multiple lentigines, Legius and others) - all stem from overactive RAS-MAPK signalling, sharing overlapping features that gene panels now untangle.
Why trust this guide
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Editorial team
Written by our editorial team from the UK sources listed on each page.
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Sourced from guidance
Checked against current NHS and UK specialist society guidance at the time of review.
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Current for 2026
Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.
Key facts
The essentials at a glance.
Which gene and test confirm it, who should be tested in the family, and which specialist to see.
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A family of conditions caused by variants in RAS-MAPK pathway genes: PTPN11, SOS1, RAF1, BRAF, HRAS, KRAS, MAP2K1/2, SHOC2, LZTR1 and more
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Shared themes: congenital heart disease, characteristic facial features, short stature, developmental variation, skin and hair findings and, for some genes, tumour predisposition
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The specific gene matters: HRAS (Costello) carries meaningful tumour surveillance needs; RAF1 flags cardiomyopathy; SPRED1 (Legius) is far milder than the NF1 it mimics
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Diagnosis is by multi-gene RASopathy panel, increasingly done in infancy - but adults with historical clinical labels benefit from testing too
Understanding the condition
What it is and what happens next.
What causes it, how it is confirmed, and the testing and specialist routes available in the UK.
What it is and how it presents
RAS-MAPK signalling is a growth-control cascade used by nearly every cell, and each RASopathy corresponds to a different component jammed partly on - which explains both the family resemblance across these syndromes and the gene-by-gene differences that clinical examination alone cannot resolve. The stakes of precision are practical: a child labelled 'Noonan-like' decades ago may actually carry HRAS, with its solid-tumour screening schedule, or SPRED1, with a reassuring outlook mistaken for neurofibromatosis; cardiac surveillance intensity, cancer vigilance and recurrence counselling all hang on the exact gene.
Testing, surveillance and specialist care
A RASopathy gene panel from blood resolves most cases at any age, and genetics services then match management templates to genotype - cardiology intervals, growth and endocrine input, tumour screening where indicated - and provide family cascade testing with reproductive counselling. Adults never molecularly confirmed are a group for whom updated testing frequently changes something concrete. NHS clinical genetics services carry some of the longest waits in the health service, often many months for a first appointment, whereas private genetic testing and a specialist review can typically be arranged within around two weeks.
Seeing a specialist
Who to see, and how quickly you can be seen.
The specialist for this condition is usually a clinical geneticist. Your GP can refer you on the NHS, or you can arrange a private consultation directly.
A quiet reminder
This guide is for information, not medical advice.
Your GP knows your history and can tell you which parts apply to you. If in doubt, see them - and seek urgent care for any emergency symptoms.
Frequently asked
Common questions about RASopathies.
Quick, plain-English answers to what people ask us most.
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What are RASopathies?
RASopathies are a group of genetic conditions - including Noonan syndrome, cardiofaciocutaneous syndrome, Costello syndrome and related conditions - that all arise from overactive signalling in the RAS-MAPK cell growth pathway. They share overlapping physical features, which is why gene panel testing is now used to distinguish between them.
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What causes RASopathies?
RASopathies are caused by mutations in genes within the RAS-MAPK signalling pathway, a system that controls cell growth and development. Most arise as new mutations, though some are inherited from an affected parent.
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What are the symptoms of a RASopathy?
Common features across this group include distinctive facial features, short stature, heart defects, developmental or learning differences, and skin changes, though the exact combination and severity varies considerably between the specific conditions and between individuals.
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Are RASopathies serious?
Severity varies widely - some features like heart defects need active monitoring and sometimes surgery, while others such as facial differences have no health impact. Most people with RASopathies live full lives with appropriate monitoring and support.
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How are RASopathies diagnosed?
Diagnosis is increasingly made through gene panel testing that looks at the several genes known to cause RASopathies, often prompted by a combination of clinical features rather than any single symptom.
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How are RASopathies treated?
There is no single treatment, but management is tailored to the specific features present - cardiology follow-up for heart defects, growth hormone therapy in some cases of short stature, and educational support for developmental differences.
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RASopathies vs Noonan syndrome - what's the difference?
Noonan syndrome is the most common and best-known RASopathy; the term RASopathy is the umbrella name for the whole family of related conditions caused by mutations in the same signalling pathway, of which Noonan syndrome is one example.
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When should I see a specialist about a possible RASopathy?
If a child or adult has a combination of distinctive facial features, unexplained short stature and heart problems, ask for referral to a clinical geneticist. A private clinical geneticist can typically be seen within about two weeks, against often much longer routine NHS genetics waits.