Neurofibromatosis-Noonan Syndrome

What causes it

NFNS belongs to a group of conditions called RASopathies, caused by changes in genes of the RAS-MAPK pathway, which controls cell growth and development. Both NF1 and Noonan syndrome are RASopathies, which explains the overlap.

In most people with NFNS, the cause is a variant in the NF1 gene, often in specific regions of the gene. Rarely, a person has both an NF1 variant and a variant in a Noonan syndrome gene such as PTPN11.

Inheritance is autosomal dominant: an affected person has a 50% chance of passing it to each child. About half of NF1 cases arise from new gene changes, with no family history.

Signs and symptoms

Neurofibromatosis type 1 features

• café-au-lait macules: flat, light brown patches, typically 6 or more
• freckling in the armpits and groin
• neurofibromas: soft, benign nerve-sheath tumors on or under the skin, and plexiform neurofibromas, larger tumors along nerves
• Lisch nodules: harmless spots on the iris
• optic pathway glioma, a usually slow-growing tumor of the optic nerve in young children
• bone differences: scoliosis, bowing of the shin bones
• learning and attention difficulties

Noonan syndrome features

• wide-spaced, down-slanting eyes, droopy eyelids and epicanthal folds
• low-set, backward-rotated ears
• a short or webbed neck and low hairline at the back
• short stature
• chest shape differences (pectus)
• heart defects: pulmonary valve stenosis is the most common; hypertrophic cardiomyopathy occasionally
• feeding difficulties in infancy
• delayed puberty

The combination and severity vary greatly between individuals.

Diagnosis

• clinical examination for NF1 and Noonan features by a geneticist
• genetic testing of NF1 and, if negative, Noonan genes (often as a RASopathy panel)
• heart evaluation: echocardiogram and ECG
• eye examination by an ophthalmologist
• growth assessment and developmental testing
• MRI if symptoms suggest brain, spine or nerve tumors

Management

There is no cure. Care follows NF1 and Noonan syndrome guidelines:

• regular skin checks and monitoring of neurofibromas; surgery for problematic tumors
• MEK inhibitors (such as selumetinib) for symptomatic, inoperable plexiform neurofibromas in children
• yearly eye exams in early childhood for optic glioma
• heart care: cardiology follow-up; balloon valvuloplasty or surgery for significant pulmonary stenosis
• blood pressure checks at least yearly (NF1 carries a risk of renal artery stenosis and pheochromocytoma)
• growth monitoring; growth hormone is sometimes used for short stature in Noonan syndrome after specialist assessment
• developmental and educational support: early intervention, speech therapy, school accommodations
• scoliosis and bone monitoring
• bleeding evaluation before surgery, as some people with Noonan features have bleeding tendencies
• genetic counseling for families

Adults with NF1 features need ongoing checks, including breast cancer screening from age 30 in women, because NF1 increases breast cancer risk.

Outlook

Outlook depends on the severity of heart disease, tumors and learning difficulties. Many people with NFNS live independent lives with regular monitoring and timely treatment.

Frequently asked questions

What is neurofibromatosis-Noonan syndrome?

It is a rare genetic condition with features of both neurofibromatosis type 1 (such as café-au-lait spots and neurofibromas) and Noonan syndrome (such as distinctive facial features, short stature and heart defects). It is usually caused by a change in the NF1 gene.

Is neurofibromatosis-Noonan syndrome inherited?

It can be. It follows an autosomal dominant pattern, so each child of an affected parent has a 50% chance of inheriting it. Many cases result from a new gene change with no family history.

What are the main health concerns in NFNS?

Key concerns include heart problems such as pulmonary valve stenosis, nerve tumors (neurofibromas and optic gliomas), learning difficulties, short stature, scoliosis and high blood pressure. Regular specialist monitoring helps catch problems early.

How is neurofibromatosis-Noonan syndrome treated?

There is no cure. Treatment addresses specific problems: heart procedures for valve narrowing, surgery or MEK inhibitors for problematic tumors, growth and developmental support, and regular checks of the skin, eyes and blood pressure.