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Legius Syndrome

What Is Legius Syndrome?

Legius syndrome is a rare genetic condition. It is one in a group of conditions called RASopathies (raz-OP-uh-thees). These happen when there's a problem in the way cells in the body communicate.

Legius syndrome (LEE-jus SIN-drome) can cause brown spots on the skin, freckles in the armpits, and learning problems. Kids with the condition can manage its symptoms with regular medical care, and have no limits on their activities.

It's also known as neurofibromatosis type 1-like syndrome (NF1-like syndrome).

What Are the Signs & Symptoms of Legius Syndrome?

A child with Legius syndrome often has these signs:

  • café-au-lait spots (named for their color, meaning "coffee with milk") that are:
    • darker than surrounding skin
    • more than 1/4-inch (5 millimeters) across
    • usually visible by the time the child is 1 year old
  • wide-set eyes
  • freckles in the armpits or in the crease between the child's belly and hip (the inguinal fold) by age 6
  • a head that looks large for the child's body
  • a breastbone (sternum) that looks pushed in (pectus excavatum) or pushed out (pectus carinatum)

Other symptoms may appear as the child grows. Kids with Legius syndrome often are slower to walk, talk, and reach other milestones than most kids. They might:

  • have trouble learning
  • have attention problems and hyperactivity
  • be shorter than other children their age

The signs and symptoms of Legius syndrome can look like those of a more serious genetic problem called neurofibromatosis.

What Causes Legius Syndrome?

Legius syndrome happens because of a change (mutation) in a gene that cells use to make a protein that:

  • helps control how cells grow
  • affects a growth-control system in the RAS pathway

Sometimes, Legius syndrome runs in families. A parent who has it has a 50% chance of passing it to a child. Other times, the change is "spontaneous." This means that a child has the condition but the parents do not. This called a new mutation.

How Is Legius Syndrome Diagnosed?

At birth, the delivery team may notice the baby's wide-set eyes and suggest genetic testing. But in most cases, doctors find the condition only after other signs happen, such as café-au-lait spots.

To make the diagnosis, the doctor will:

  • ask about the child's symptoms and signs
  • ask about the family history of genetic conditions
  • do an exam
  • do genetic testing

Doctors may look for brain and bone problems by doing X-rays or an MRI.

How Is Legius Syndrome Treated?

Often, it's a genetics doctor who diagnoses a child with Legius syndrome. But follow-up care usually is routine, and managed by a pediatrician or family practice doctor.

There's no cure for Legius syndrome. Treatment focuses on managing the symptoms, and may include:

What Else Should I Know?

Children with Legius syndrome do not need close medical monitoring. They have no limits on their activities and have a full life expectancy.

To understand how Legius syndrome can run in families, genetic testing and prenatal genetic counseling may be helpful for:

  • parents and extended family members (aunts, uncles, cousins) of a child with Legius syndrome
  • adults with Legius syndrome

Reviewed by: Karen W. Gripp, MD
Date Reviewed: Sep 2, 2019

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