Cause
This section discusses the tumorigenesis of neurofibroma in terms of genetics, cell signaling, histology and the cell cycle. Neurofibromin 1 gene
The NF1 gene is composed of 60 exons spanning 350kb of genomic data, and maps to chromosomal region 17qll.2. This gene codes for neurofibromin which is a large 220-250 KDa cytoplasmic protein that is composed of 2,818 amino acids with three alternatively spliced exons (9a, 23a and 48a) in the encoding gene. The functional part of neurofibromin is a GAP, or GTPase-activating protein. GAP accelerates the conversion of the active GTP-bound RAS to its inactive GDP-bound form, inactivating RAS and reducing RAS-mediated growth signaling. Loss of RAS control leads to increased activity of other signaling pathways including RAF, ERK1/2, PI3K, PAK and mTOR-S6 kinase. This increased activity of downstream RAS pathways might work together to increase cell growth and survival. Genes that code for proteins that regulate cell growth, such as NF1 and TP53, are referred to as tumor suppressor genes. Neurofibromin has other growth-regulatory properties besides its ability to regulate RAS activity, but these other functions are poorly understood at this time. Schwann cells
There are two kinds of Schwann cells, myelinating and nonmyelinating. While myelinating Schwann cells cover large diameter (>1 micrometer) peripheral nervous system (PNS) axons with myelin, nonmyelinating Schwann cells encapsulate small diameter PNS axons with their cytoplasmic processes. Nonmyelinating Schwann cells are the neoplastic element in neurofibromas. This conglomeration of nonmyelinating Schwann cells and axons is called a Remak bundle.
Hyperprolinemia is a condition which occurs when the amino acid proline is not broken down properly by the enzymes proline oxidase or pyrroline-5-carboxylate dehydrogenase, causing a buildup of proline in the body. Genetics
Mutations in the ALDH4A1 and PRODH genes cause hyperprolinemia.Hyperprolinemia type I is caused by a mutation in the PRODH gene, which codes for the enzyme proline oxidase. This enzyme begins the process of degrading proline by starting the reaction that converts it to pyrroline-5-carboxylate.Hyperprolinemia type II is caused by a mutation in the ALDH4A1 gene, for the enzyme 1-pyrroline-5-carboxylate dehydrogenase. This enzyme helps to break down the pyrroline-5-carboxylate produced in the previous reaction, converting it to the amino acid glutamate. The conversion between proline and glutamine, and the reverse reaction controlled by different enzymes, are important factors required to maintain proper metabolism and protein production. A deficiency of either proline oxidase or pyrroline-5-carboxylate dehydrogenase results in a buildup of proline in the body. A deficiency of the latter enzyme leads to higher levels of proline and a buildup of the intermediate breakdown product pyrroline-5-carboxylate, causing the signs and symptoms of hyperprolinemia type II.Hyperprolinemia is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered.