Nearly all individuals show multiple café au lait spots.Features common in neurofibromatosis - Lisch nodules, bone abnormalities, neurofibromas, optic pathway gliomas and malignant peripheral nerve sheath tumors - are absent in this condition Symptoms however, may include:

- Freckles

- Lipomas

- Macrocephaly

- Learning disabilities

- ADHD

- Developmental delay

The following is a list of conditions and complications associated with NF-1, and, where available, age range of onset and progressive development, occurrence percentage of NF-1 population, method of earliest diagnosis, and treatments and related medical specialties. The progression of the condition is roughly as follows:

1. Congenital musculoskeletal disorders may or may not be present

2. Cutaneous conditions may be observed in early infancy

3. Small tumors may arise in the retina which can eventually lead to blindness. Also, Lisch Nodules may grow on the iris, but these are harmless.

4. Learning disabilities may arise in preschool children

5. Neurofibromas may occur and can sometimes cause many dependent neurological conditions and cutaneous and skeletal disfigurement.

6. Depression and social anxiety may occur as a result of disabilities caused by the condition

7. Neurofibromas may, in rare and extreme cases, transition into cancer, which can be fatal

The NF Clinical Program at St. Louis Children's Hospital maintains a comprehensive list of current NF research studies.

Musculoskeletal abnormalities affecting the skull include Sphenoid bone dysplasia, Congenital Hydrocephalus and associated neurologic impairment. These abnormalities are non-progressive and may be diagnosed in the fetus or at birth.

Disorders affecting the spine include:

- In NF-1, there can be a generalized abnormality of the soft tissues in the fetus, which is referred to as mesodermal dysplasia, resulting in maldevelopment of skeletal structures.

- Meningoceles and formation of cystic diverticula of the dura of the spine, unrelated to Spina bifida

- Radiographically, Dural ectasia can lead to scalloping of the posterior vertebral bodies and to the formation of cystic diverticula of the dura of the spine (termed meningoceles. This meningocele is not related to spina bifida).

- Focal scoliosis and/or kyphosis are the most common skeletal manifestation of NF-1, occurring in 20% of affected patients. Approximately 25% of patients will require corrective surgery.

Skeletal muscle weakness and motor control deficits

Deficits in motor function in NF-1 have been long recognised and have been historically attributed to nerve dysfunction. In recent years however, studies suggest NF-1 is associated with a primary problem in muscle function (myopathy).

Clinical findings in people with NF-1 include:

- Reduced skeletal muscle size

- Reduced exercise capacity

- Muscle weakness (The most recent study reports between 30–50% reduced upper and lower limb muscle strength in NF-1 children compare with matched controls ).

Studies in genetically modified mice have thus far confirmed that the NF1 gene is vital for normal muscle development and metabolism. Knockout of the NF1 gene in muscle results in deregulated lipid metabolism and muscle weakness.

It is interesting to note that NF-1 is a disease in the RASopathy family of diseases, which include Costello Syndrome, Noonan Syndrome, and Cardiofaciocutaneous syndrome. The RASopathies also present with skeletal muscle weakness. It is likely that impaired muscle function in these disorders is linked to altered Ras/MAPK signalling, however, the precise molecular mechanisms remain unknown.

An alternative name of the condition, LEOPARD syndrome, is a mnemonic, originally coined in 1969, as the condition is characterized by some of the following seven conditions, the first letters of which spell LEOPARD, along with the characteristic "freckling" of the skin, caused by the lentigines that is reminiscent of the large cat.

- Lentigines — Reddish-brown to dark brown macules (surface skin lesion) generally occurring in a high number (10,000+) over a large portion of the skin, at times higher than 80% coverage. These can even appear inside the mouth (buccal), or on the surface of the eye (scleral). These have irregular borders and range in size from 1 mm in diameter to café-au-lait spots, several centimeters in diameter. Also, some areas of vitiligo-like hypopigmentation may be observed.

- Electrocardiographic conduction abnormalities: Generally observed on an electrocardiograph as a bundle branch block.

- Ocular hypertelorism: Wideset eyes, which lead to a similar facial resemblance between patients. Facial abnormalities are the second highest occurring symptom after the lentigines. Abnormalities also include: broad nasal root, prognathism (protruding lower jaw), or low-set, possibly rotated, ears.

- Pulmonary stenosis: Narrowing of the pulmonary artery as it exits the heart. Other cardiac abnormalities may be present, including aortic stenosis, or mitral valve prolapse.

- Abnormal genitalia: usually cryptorchidism (retention of testicles in body) or monorchism (single testicle). In female patients, this presents as missing or single ovaries, much harder by nature to detect. Ultrasound imaging is performed at regular intervals, from the age of 1 year, to determine if ovaries are present.

- Retarded growth: Slow, or stunted growth. Most newborns with this syndrome are of normal birth weight and length, but will often slow within the first year.

- Deafness: Sensorineural (nerve deafness).

The presence of all of these hallmarks is not needed for a diagnosis. A clinical diagnosis is considered made when, with lentigines present there are 2 other symptoms observed, such as ECG abnormalities and ocular hypertelorism, or without lentigines, 3 of the above conditions are present, with a first-degree relative (i.e. parent, child, sibling) with a clinical diagnosis.

- Additional dermatologic abnormalities (axillary freckling, localized hypopigmentation, interdigital webbing, hyperelastic skin)

- Mild mental retardation is observed in about 30% of those affected with the syndrome

- Nystagmus (involuntary eye movements), seizures, or hyposmia (reduced ability to smell) has been documented in a few patients

- In 2004, a patient was reported with recurrent upper extremity aneurysms that required surgical repairs.

- In 2006, a NSML patient was reported with acute myelogenous leukemia.

Due to the rarity of the syndrome itself, it is hard to determine whether certain additional diseases are actually part of the syndrome. With a base population of possibly less than one thousand individuals, one or two outlying cases can skew the statistical population very quickly.

Legius syndrome (LS) is an autosomal dominant condition characterized by cafe au lait spots. It was first described in 2007 and is often mistaken for neurofibromatosis type I (NF-1), it is caused by mutations in the SPRED1 gene, it is also known as Neurofibromatosis Type 1-like syndrome (NFLS). The condition is a RASopathy, developmental syndromes due to germline mutations in genes

Noonan syndrome with multiple lentigines (NSML) which is part of a group called Ras/MAPK pathway syndromes, is a rare autosomal dominant, multisystem disease caused by a mutation in the protein tyrosine phosphatase, non-receptor type 11 gene ("PTPN11"). The disease is a complex of features, mostly involving the skin, skeletal and cardiovascular systems, which may or may not be present in all patients. The nature of how the mutation causes each of the condition's symptoms is not well known; however, research is ongoing. It is a RASopathy.

Noonan syndrome with multiple lentigines is caused by a different missense mutation of the same gene. Noonan syndrome is fairly common (1:1,000 to 1:2,500 live births), and neurofibromatosis 1 (which was once thought to be related to NSML) is also common (1:3500); however, no epidemiological data exists for NSML.

Gingival fibromatosis with hypertrichosis is a cutaneous condition characterized by dark terminal hairs on the peripheral face, central back, and extremities. It is a RASopathy.

Costello syndrome, also called faciocutaneoskeletal syndrome or FCS syndrome, is a rare genetic disorder that affects many parts of the body. It is characterized by delayed development and delayed mental progression, distinctive facial features, unusually flexible joints, and loose folds of extra skin, especially on the hands and feet. Heart abnormalities are common, including a very fast heartbeat (tachycardia), structural heart defects, and overgrowth of the heart muscle (hypertrophic cardiomyopathy). Infants with Costello syndrome may be large at birth, but grow more slowly than other children and have difficulty feeding. Later in life, people with this condition have relatively short stature and many have reduced levels of growth hormones. It is a RASopathy.

Beginning in early childhood, people with Costello syndrome have an increased risk of developing certain cancerous and noncancerous tumors. Small growths called papillomas are the most common noncancerous tumors seen with this condition. They usually develop around the nose and mouth or near the anus. The most frequent cancerous tumor associated with Costello syndrome is a soft tissue tumor called a rhabdomyosarcoma. Other cancers also have been reported in children and adolescents with this disorder, including a tumor that arises in developing nerve cells (neuroblastoma) and a form of bladder cancer (transitional cell carcinoma).

Costello Syndrome was discovered by Dr Jack Costello, a New Zealand Paediatrician in 1977. He is credited with first reporting the syndrome in the Australian Paediatric Journal, Volume 13, No.2 in 1977.

Up to ~85% of people with NS have one of the following heart defects:

- Pulmonary valvular stenosis (50–60%)

- Septal defects: atrial (10–25%) or ventricular (5–20%)

- Hypertrophic cardiomyopathy (12–35%)

Noonan syndrome (NS) is a relatively common autosomal dominant congenital disorder and is named after Jacqueline Noonan, a pediatric cardiologist. It is referred to as the male version of Turner's syndrome; however, the genetic causes of Noonan syndrome and Turner syndrome are distinct and both males and females are affected. The principal features include congenital heart defect (typicall pulmonary valve stenosis with dysplastic pulmonary valve also atrial septal defect and hypertrophic cardiomyopathy), short stature, learning problems, pectus excavatum, impaired blood clotting, and a characteristic configuration of facial features including a webbed neck and a flat nose bridge. NS is a RASopathy, and is one of several disorders that are caused by a disruption of RAS-MAPK signaling pathway.

It is believed that between approximately 1 in 1,000 and 1 in 2,500 children worldwide are born with NS. It is one of the most common genetic syndromes associated with congenital heart disease, similar in frequency to Down syndrome. However, the range and severity of features can vary greatly in patients with NS. Therefore, the syndrome is not always identified at an early age.

All people with ALPS have signs of lymphoproliferation, which makes it the most common clinical manifestation of the disease. The increased proliferation of lymphoid cells can cause the size of lymphoid organs such as the lymph nodes and spleen to increase (lymphadenopathy and splenomegaly, present in respectively over 90% and over 80% of patients). The liver is enlarged (hepatomegaly in 30 - 40% of patients).

Autoimmune disease is the second most common clinical manifestation and one that most often requires treatment. Autoimmune cytopenias: Most common. Can be mild to very severe. Can be intermittent or chronic. These include: Autoimmune hemolytic anemia, Autoimmune neutropenia, Autoimmune thrombocytopenia.

Other signs can affect organ systems similar to systemic lupus erythematosus (least common, affecting <5% of patients) Symptoms of the nervous system include: Autoimmune cerebellar ataxia; Guillain–Barré syndrome; transverse myelitis. Gastrointestinal signs like Autoimmune esophagitis, gastritis, colitis, hepatitis, pancreatitis can be found or (Dermatologic) Urticaria, (Pulmonary) bronchiolitis obliterans, (Renal) Autoimmune glomerulonephritis, nephrotic syndrome.

Another sign are cancers such as Hodgkin and non-Hodgkin lymphomas which appear to be increased, possibly due to Epstein–Barr virus-encoded RNA-positivity. Some carcinomas may occur. Unaffected family members with genetic mutations are also at an increased risk of developing cancer.

2003 nomenclature

- IA - Fas

- IB - Fas ligand

- IIA - Caspase 10

- IIB - Caspase 8

- III - unknown

- IV - Neuroblastoma RAS viral oncogene homolog

Revised nomenclature (2010)

- ALPS-FAS: Fas. Germline FAS mutations. 70% of patients. Autosomal dominant. Dominant negative and haploinsufficient mutations described.

- ALPS-sFAS: Fas. Somatic FAS mutations in DNT compartment. 10% of patients

- ALPS-FASL: Fas ligand. Germline FASL mutations. 3 reported cases

- ALPS-CASP10: Caspase 10. Germline CASP10 mutation. 2% of patients

- ALPS-U: Undefined. 20% of patients

- CEDS: Caspase 8 deficiency state. No longer considered a subtype of ALPS but distinct disorder

- RALD: NRAS, KRAS. Somatic mutations in NRAS and KRAS in lympocyte compartment. No longer considered a subtype of ALPS but distinct disesase

Costello syndrome is caused by any of at least five different mutations in the "HRAS" gene on chromosome 11. This gene provides instructions for making a protein, H-Ras, that helps control cell growth and division. Mutations that cause Costello syndrome lead to the production of an H-Ras protein that is permanently active. Instead of triggering cell growth in response to particular signals from outside the cell, the overactive protein directs cells to grow and divide constantly. This unchecked cell division may predispose sufferers to the development of benign and malignant tumors. It remains unclear how mutations in "HRAS" cause other features of Costello syndrome, but many of the signs and symptoms may result from cell overgrowth and abnormal cell division.

"HRAS" is a proto-oncogene in which somatic mutations in healthy people can contribute to cancer. Whereas children with Costello syndrome typically have a mutation in "HRAS" in every cell of their bodies, an otherwise healthy person with a tumor caused in part by "HRAS" mutation will only have mutant "HRAS" within the tumor. The test for the mutation in cancer tumors can also be used to test children for Costello syndrome.

Costello syndrome is inherited in an autosomal dominant manner, which means one copy of the altered gene is sufficient to cause the disorder. Almost all cases have resulted from new mutations, and occur in people with no history of the disorder in their family. This condition is rare; as of 20 April 2007, 200 to 300 cases have been reported worldwide.