• The type of inheritance pattern is called autosomal dominant: any offspring of a person with NF1 will have a 50% chance of inheriting the abnormal NF1 gene and eventually showing at least some signs of NF1.

• Children who do not inherit the abnormal gene do not develop the condition, nor can they transmit it to their own offspring.

• Diagnosis is clinical, based on the presence of certain features detected by physical examination.

• Gene testing is possible but not usually necessary to confirm diagnosis. Families with concerns or questions about recurrence of NF1 can be offered genetic counselling and discussion of options for prenatal diagnosis and diagnosis at IVF

These are flat, coffee-coloured birthmarks varying from freckle-sized to very large. People with NF1 usually have at least six of these, but may have many more. The most common way for the diagnosis of NF1 to be suspected is when multiple café au lait spots are noticed. Freckling in unusual places, such as the armpit or groin, is also common.

Neurofibromas are benign skin lumps growing around nerves, in or just beneath the skin. They are pea-sized or larger, and develop over time, so may be absent or few in number in childhood. For people with NF1 neurofibromas tend to increase in number during puberty or pregnancy and most adults with NF1 have at least some, some have hundreds, and some people do not develop any obvious neurofibromas. Although neurofibromas can be surgically removed, they leave a scar and tend to regrow. Neurofibromas cannot be transmitted from one person to another.

These are small pigmented nodules in the iris of the eye. They are harmless, often not visible without a special microscope, and are mainly important because their presence helps in diagnosis.

Learning difficulties are one of the most common and challenging complications of NF1. Research suggests that most students with NF1 under-perform at school and about 50% of them experience a learning difficulty. Areas of underachievement encompass a range of academic skills including reading, spelling, mathematics, and problem-solving, with no single area predominately affected.

Download: Neurofibromatosis type 1: managing student learning (.pdf 69kB) to learn more.

Download: Neurofibromatosis type 1: student learning (.pdf 68kB) to learn more.

Although there are many other possible features of NF1, most occur in a minority of people with the condition.

• An important possible complication of NF1 in early childhood is the development of optic gliomas. These are tumours involving the nerves to the eye (the optic nerves). The tumours are benign, usually small, and may cause no problems.

• Plexiform neurofibromas are larger tumours which involve nerves and can cause overgrowth of tissues resulting in large lumps, areas of increased pigment, asymmetry of the face or overgrowth of a limb.

• Major bone conditions, such as marked bowing of the tibia (shin bone) occur in less than 2% of people and are obvious during the first two years of life.

• Macrocephaly (large head) is found in about one in three people with NF1.

• About one in three people with NF1 are shorter than would be expected for their family background. It is important to check for scoliosis (curvature of the spine) as this may develop in childhood or adolescence, and may require surgery.

• Headaches and migraines, high blood pressure, and epilepsy are more common in children and adults with NF1 than in the unaffected population.

• Other types of brain and spinal tumours can occur, but these will affect less than 5% of people over a lifetime.

• Cancer (malignancy) related to NF1 occurs in about 5% of people over a lifetime.

• Hearing impairment is probably no more common in children with NF1 than in any other child and occurs for the same reasons (eg in association with glue ear). Hearing difficulties due to tumours are a major feature in adults with the quite separate disorder, neurofibromatosis type 2 (NF2).

Two or more features must be present to confirm the diagnosis. It is important to remember that most people with NF1 never develop all these features; the first four listed are the most frequent and are present in nearly all adults with NF1.

• six or more café au lait spots, greater than 5 mm in diameter (before puberty), and greater than 15 mm (after puberty)

• two or more neurofibromas or one plexiform neurofibroma

• freckles in the axilla (armpit) or groin

• Lisch nodules in the iris

• optic glioma — a tumour of the optic nerve

• characteristic skeletal abnormality (eg bowing of the tibia)

• NF1 by above criteria in parent, sibling or offspring.

Medical management

Although many children with NF1 will be healthy and without major complications, it is recommended that all are regularly checked (at least once a year) by a doctor who is familiar with the condition. This is usually a paediatrician, clinical geneticist or neurologist. In addition at least annual eye checks by an ophthalmologist are recommended until age 10. Other specialists may be involved for children with complications such as scoliosis.