The progression of the condition is roughly as follows:

Congenital musculoskeletal disorders may or may not be present
Cutaneous conditions may be observed in early infancy
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. Learning disabilities may arise in preschool children
Neurofibromas may occur and can sometimes cause many dependent neurological conditions and cutaneous and skeletal disfigurement. Depression and social anxiety may occur as a result of disabilities caused by the condition
Neurofibromas may, in 8-13% of cases, transition into cancer, which can be fatal The NF Clinical Program at St. Louis Childrens Hospital maintains a comprehensive list of current NF research studies Archived 2015-11-26 at the Wayback Machine. Musculoskeletal disorder
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. This may result in temporary or permanent loss of lower extremity sensorimotor function. Focal scoliosis and/or kyphosis are the most common skeletal manifestation of NF-1, occurring in 20% of affected patients.
Furthermore, the heights of children affected by NF-1 have been shown to increase normally until puberty, after which increases in height lessen when compared to healthy counterparts. This eventually causes a shorter stature than expected in individuals with NF-1. Cancer
Cancer can arise in the form of malignant peripheral nerve sheath tumor resulting from malignant degeneration of a plexiform neurofibroma. Frequency. A plexiform neurofibroma has a lifetime risk of 8–12% of transformation into a malignant tumor. Diagnosis. MRI. Treatment. Surgery (primary), radiation therapy. Mortality. Malignant nerve sheath tumor was the main cause of death (60%) in a study of 1895 patients with NF-1 from France in the time period 1980–2006 indicated excess mortality in NF-1 patients compared to the general population. The cause of death was available for 58 (86.6%) patients. The study found excess mortality occurred among patients aged 10 to 40 years. Significant excess mortality was found in both males and females. Cause
Neurofibromin 1 gene
NF-1 is a microdeletion syndrome caused by a mutation of a gene located on chromosomal segment 17q11.2 on the long arm of chromosome 17 which encodes a protein known as neurofibromin (not to be confused with the disorder itself) which plays a role in cell signaling. The Neurofibromin 1 gene is a negative regulator of the Ras oncogene signal transduction pathway. It stimulates the GTPase activity of Ras. It shows greater affinity for RAS p21 protein activator 1, but lower specific activity. The mRNA for this gene is subject to RNA editing (CGA->UGA->Arg1306Term) resulting in premature translation termination.