The neurofibromas caused by NF consist of Schwann cells, fibroblasts, perineuronal cells, mast cells and axons embedded in an extracellular matrix. Another function of neurofibromin is to bind to microtubules that play a role in the release of adenylyl cyclase and its activity. Adenylyl cyclase plays an essential role in cognition. Neurofibromins role in the activity of adenylyl cyclase explains why patients with NF experience cognitive impairment.Neurofibromatosis type II is caused by a mutation on chromosome 22. The mutation falls on the NF2 tumor suppressor gene. The gene normally encodes a cytoplasmic protein known as merlin. The normal function of merlin is to regulate the activity of multiple growth factors, the mutated copy of the gene leads to merlins loss of function. The loss of function leads to increased activity of growth factors normally regulated by merlin, leading to the formation of the tumors associated with NF2.Schwannomatosis is caused by a mutation on the SMARCB1 gene. This gene is located near the NF2 tumor suppressor gene leading to the thought that schwannomatosis and NF2 were the same condition. The two conditions show different mutations on two different genes. The normal function of the SMARCB1 gene is to encode a protein called SMARCB1 that is part of a larger protein complex whose function is not completely understood. The complex including SMARCB1 plays a role in tumor suppression. The mutation of the SMARCB1 gene causes a loss of function in the complex leading to the formation of tumors indicative of schwannomatosis.
Schneckenbecken dysplasia is a rare pre-natally fatal hereditary autosomal recessive condition which affects the bones and pre-natal growth. Signs and symptoms
Fetuses with the condition typically have a hypoplastic iliac bone which resembles a snail, short ribs, short neck, shortened and widened (dysplastic) fibula bones, premature ossification of the tarsus, shortened and broadened long bones which resemble a dumbbell, hypoplastia and flattening vertebrae, macrocephaly, dolichocephaly, toenail hypoplasia, flattening of the malar prominence, and micromelic (short-limbed) dwarfism. Complications
Fetuses homozygous for this condition typically die before being born, and because of this they dont usually live to experience the complications of the disease. Genetics
This condition is typically caused by loss-of-function mutations in the SLC35D1 gene, located in chromosome 1. These mutations are inherited in an autosomal recessive manner. Diagnosis
This condition can be diagnosed through the following methods:

Ultrasound (due to its prenatally fatal nature)
Whole genome sequencing
Physical examination
Post-mortem autopsy

Treatment
There is no cure for this disorder, and attempted treatment will always be ineffective due to this conditions lethal nature. Prevalence
According to OrphaNet, less than 20 cases have been reported. History
This condition was first discovered in 1986 by Knowles et al. when they described 5 fetuses born to a consanguineous, first-cousin Asian couple. The couple in question went through 13 pregnancies, these pregnancies consisted of 4 successful pregnancies which resulted in healthy children, 5 pregnancies which resulted in dead dwarf babies, 3 pregnancies which ended in miscarriage, and 1 pregnancy which was clinically aborted after the pre-natal detection of dwarfism.