Noonan syndrome is a genetic condition which is very variable in degree and so mildly affected individuals may remain undiagnosed. Additionally the characteristics, especially facial, appear to change as the individual ages.

Characteristics include:

• heart defects, the commonest being pulmonary valve stenosis; atrial septal defects and hypertrophic cardiomyopathy;
• facial features: ptosis (drooping eyelids); large downward slanting eyes; hypertelorism (widely spaced eyes), flat nasal bridge; short neck with or anterior rotations;
• short stature in correct proportion.

Additional features may include:

• excess oedema at birth and slow weight gain;
• feeding difficulties with poor sucking and weaning and frequent and/or forceful vomiting in babies which may be assessed as failure to thrive;
• mild hearing loss;
• dental delay;
• elevated or depressed sternum;
• hypotonia;
• undescended testes;
• mild developmental delay in a minority of children;
• speech and behaviour problems.

There is an overlap between Noonan syndrome and LEOPARD syndrome. Some cases of LEOPARD syndrome may be caused by the same gene as Noonan syndrome. The term LEOPARD stands for Lentignes (freckles), ECG (minor abnormalities in the electrical activity of the heart), Ocular hypertelorisrn (widely spaced eyes), Pulmonary stenosis, Abnormalities of the male genitalia, Retardation of growth, Deafness.

Inheritance patterns
Autosomal dominant. A gene PTPN11 on chromosome 12 has been found to account for half of all cases of Noonan syndrome.

Prenatal diagnosis
It is occasionally possible to diagnose the syndrome with ultrasound scanning.

Medical text written November 1991 by Contact a Family. Approved November 1991 by Professor M Patton and Dr J E Wraith, Consultant Paediatrician, Royal Manchester Children's Hospital, Manchester, UK. Last updated October 2004 by Professor Michael Patton, Professor of Medical Genetics, St George's Hospital Medical School, London, UK.

The Noonan Syndrome Society is no longer functioning. The Family Services Officer of the Birth Defects Foundation can provide information to families.