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# Proteus syndrome

A very rare disorder of patchy, progressive overgrowth of bones, skin and fat, caused by a mutation present in only some of the body's cells.

Updated Nov 13, 2026

On this page

- The basics What it is
- Who gets it
- Causes
- Pathophysiology

- Clinical Symptoms and signs
- Red flags
- Diagnosis
- Complications
- Prognosis

- Treatment Treatment

- Study Test yourself

## What it is

A mosaic overgrowth disorder caused by an activating variant in AKT1 that arises after conception, so only part of the body carries it.

See it in 3D

- [Femur](https://durgical.com/en/anatomy/femur/)
- [Tibia](https://durgical.com/en/anatomy/tibia/)
- [Skin](https://durgical.com/en/anatomy/skin/)

## Who gets it

Very rare: fewer than one in a million people.

## Causes

- Somatic (postzygotic) activating variant in AKT1, almost always p.Glu17Lys
- Not inherited: the variant is thought to be lethal if present in every cell

## Pathophysiology

AKT1 is a kinase in the PI3K–AKT pathway that promotes cell growth and survival. The variant keeps it switched on, so the tissues that carry it overgrow; because only a mosaic of cells is affected, overgrowth is patchy and asymmetric and usually appears after the first months of life.

## Symptoms and signs

- Asymmetric, progressive overgrowth of limbs, digits or skull, starting at about 6–18 months
- Cerebriform connective-tissue naevus, a thick furrowed lesion on the soles
- Epidermal naevi
- Areas of fat overgrowth or loss
- Vascular malformations

## Red flags

- Sudden breathlessness or [chest](https://durgical.com/en/anatomy/region/chest/) pain (pulmonary embolism)
- A painful swollen limb (deep vein thrombosis)

## Diagnosis

**Clinical**
Clinical criteria: mosaic distribution, progressive course and sporadic occurrence, plus specific features such as the cerebriform naevus.

**Tests**
Finding the AKT1 variant in affected tissue ([skin](https://durgical.com/en/anatomy/skin/) or overgrown tissue); blood is often negative because of mosaicism.

**Imaging**
X-rays and other imaging map bone overgrowth and vascular malformations.

## Treatment

**Surgical**
Orthopaedic surgery to slow uneven growth and correct deformity.

**Follow-up**
Regular follow-up of overgrowth and awareness of the high risk of venous thrombosis, especially after surgery.

**Medical**
AKT inhibitors are being studied in clinical trials.

**Rehabilitation**
Physical therapy and psychological support.

## Complications

- Deep vein thrombosis and pulmonary embolism, a leading cause of death
- Severe limb deformity and joint problems
- Certain tumours

## Prognosis

Overgrowth progresses through childhood; life expectancy is reduced mainly by thrombosis.

## Test yourself

Think of the answer, then tap the question to see it.

## Why is Proteus syndrome never inherited?

It is caused by a mosaic AKT1 variant that arises after conception; the variant in every cell is thought to be lethal.

## Why may a blood test fail to find the AKT1 variant?

The variant is present only in some tissues; testing affected skin or overgrown tissue is more sensitive.

## What is the most important life-threatening complication?

Venous thrombosis and pulmonary embolism.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Proteus syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/proteus-syndrome/) (MedlinePlus, US National Library of Medicine, 2026); [AKT1 gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/akt1/) (MedlinePlus, US National Library of Medicine, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/conditions/proteus-syndrome/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/proteus-syndrome/