SMARCB1 is mutated in additional tumors including malignant brain & kidney tumors in children. It seems that heterozygotes for mutations in the SMARCB1 gene have an increased risk to develop a malignant kidney tumor in early childhood but if they survive to adulthood, they may be predisposed to the development of schwannomas. One schwannomatosis patient had a mutation in exon 2 of the SMARCB1 gene. Another patient exhibited a novel germline deletion of the SMARCB1, because most SMARCB1 mutations are point or frameshift. In this patient genetic analysis from different schwannomas indicated  inactivation of both the SMARCB1 and NF2 genes. Schwannomatosis is known to be a genetic disorder. However, familial occurrence is inexplicably rare. Diagnosis
Prenatal
Schwannomatosis can be tested prenatally on the NHS. Postnatal
Ferner et al. give the following diagnostic criteria for Schwannomatosis:

Definite
Age >30 years and ≥2 nonintradermal schwannomas, at least one with histologic confirmation and no evidence of vestibular tumor on MRI scan and no known NF mutation, or
One nonvestibular schwannoma plus a first-degree relative with schwannomatosis
Possible
Age <30 and ≥2 nonintradermal schwannomas, at least one with histologic confirmation and no evidence of vestibular tumor on MRI scan and no known NF mutation, or
Age >45 and ≥2 nonintradermal schwannomas, at least one with histologic confirmation and no symptoms of 8th nerve dysfunction and no NF2, or
Nonvestibular schwannoma and first-degree relative with schwannomatosis
Segmental.
Success rates, although limited in data, appear to be in the low to mid ninety percent range. As most schwannomas are benign, many doctors will take the “watch and wait” approach and leave the tumors alone until they start causing harmful side effects. Schwannomatosis patients have multiple tumors and the risks of having so many surgeries outweigh the benefits. Prognosis
Many of the symptoms of schwannomatosis overlap with NF2. Schwannomas occur instead of the neurofibromas that are hallmarks of neurofibromatosis Type 1 (NF1). Multiple schwannomas manifest throughout the body or in isolated regions. The schwannomas develop on cranial, spinal and peripheral nerves. Chronic pain, and sometimes numbness, tingling and weakness. About 1/3 of patients have segmental schwannomatosis, which means that the schwannomas are limited to a single part of the body, such as an arm, a leg or the spine. There are several cases where people with schwannomatosis have developed a vestibular schwannoma (acoustic neuroma). An acoustic neuroma is a schwannoma on the vestibular nerve in the brain. This nerve is involved in hearing and patients with vestibular schwannomas experience hearing loss. However, bilateral vestibular schwannomas (vestibular schwannomas on both sides of the brain) do not occur in schwannomatosis. Juvenile vestibular tumors do not occur either. Patients with schwannomatosis do not have learning disabilities related to the disease. Symptoms are sometimes brought on by hormonal changes such as puberty and pregnancy. == References ==