This is a set of images from an MRI of the brain in a patient with TSC.This is an image from a contrast-enhanced CT of the abdomen in another patient with TSC.This computed tomography image shows randomly arranged cysts in both lungs.  The patient had TSC and a renal AML.
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Tuberous Sclerosis

Tuberous sclerosis, (meaning "hard potatoes"), is a rare genetic disorder primarily characterized by a triad of seizures, mental retardation, and skin lesions (called adenoma sebaceum). This "classic" Vogt triad is present in 30-50% of cases; in particular, up to 30% of tuberous sclerosis reportedly have normal mentation. Tuberous sclerosis, along with Neurofibromatosis type I, Neurofibromatosis type II (a.k.a. MISME syndrome), Sturge-Weber, and Von Hippel-Lindau compromise the Phakomatoses or neurocutaneous syndromes, all of which have neurologic and dermatologic lesions. more...

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This grouping is an artifact of an earlier time in medicine, before the distinct genetic basis of each of these diseases was understood.

The neuropathologic findings of the cortical "tubers" (sclerose tubereuse) was first described by Désiré-Magloire Bourneville in 1880.

Individuals with tuberous sclerosis may experience none or all of the symptoms with varying degrees of severity. Tuberous sclerosis is a multi-system disease that can affect the brain, kidneys, heart, eyes, lungs, and other organs. Small benign tumors may grow on the face and eyes, as well as in the brain, kidneys, and other organs. Neuroimaging studies may be able to confirm the diagnosis. Seizures most often begin in the first year of life.

Tuberous sclerosis' acronym is T.S.C. (Tuberous sclerosis complex) so as to avoid confusion with Tourette's Syndrome.

Genetics

Tuberous sclerosis (TSC) is a genetic disorder caused by mutations on either of two genes TSC1 and TSC2. It has an autosomal dominant pattern of inheritance and penetrance is 100%. The incidence is between 1/6,000 and 1/10,000. One third of cases are inherited; the rest are new mutations.

TSC1 is located on chromosome 9q34 and encodes for the protein hamartin. It was discovered in 1997. TSC2 is located on chromosome 16p13.3 and encodes for the protein tuberin. It was discovered in 1993. TSC2 is contiguous with PKD1 (which causes one form of polycystic kidney disease). Gross deletions affecting both genes may account for the 2% of individuals with TSC who develop PKD in childhood.

TSC1 and TSC2 are both tumor suppressor genes that function according to Knudson's "two hit" hypothesis. That is, a second random mutation must occur before a tumor can develop. This explains the wide expressivity of the disease. Of the two, TSC2 has been associated with a more severe form of TSC. However, the difference is subtle and statistical and cannot be used to identify the mutation clinically. Estimates of the proportion of TSC caused by TSC2 ranges from 55% to 80-90%. Current genetic tests have difficulty locating the mutation in approximately 20% of individuals.

Hamartin/tuberin function as a complex, whose biological activity appears to be a Rheb GTPase. They function within the growth factor (insulin) signalling pathway and are involved in suppressing mTOR signalling.

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Micronodular Pneumocyte Hyperplasia In Tuberous Sclerosis - Abstract
From CHEST, 10/1/99 by J. D. Christie

Introduction: Tuberous sclerosis complex (TSC) is a rare, autosomal dominant disorder. We report a patient with multiple signs of TSC, referred for evaluation of a chest radiograph showing small lung nodules.

Case Report: A 45 year-old woman was referred because of an abnormal chest radiograph. The patient reported previous good health, with no known lung diseases. She had no respiratory symptoms. One year ago, during a routine medical evaluation, the patient was noted to have an elevated serum creatinine. An abdominal CT scan revealed bilateral renal masses. Needle biopsy of one of the masses showed a "hamartomatous smooth muscle lesion similar to the elements of an angiomyolipoma." A chest radiograph showed diffuse, subcentimeter pulmonary nodules. Bronchoscopy with transbronchial biopsy was "nondiagnostic." The patient was referred for urologic evaluation and, subsequently, pulmonary consultation.

There was no history of cough, sputum production or dyspnea. The patient was able to walk several miles without shortness of breath. A seizure disorder was diagnosed four years previously and treated with diphenylhydantoin. In addition, there was a history of hypothyroidism, treated with levothyroxine. A vaginal hysterectomy was performed 10 years previously for dysfunctional uterine bleeding. The patient never smoked; there was no history of alcohol or illicit drug use. She was employed as a lien searcher and had no occupational exposures to dusts or fumes. She had not traveled outside the United States and had no pets. There was no family history of pulmonary disease. The patient's son had his first seizure at age 21 years.

On physical examination the patient was a well-appearing, thin woman. Raised red nodules were noted on the nose. The chest was symmetric and the lung fields were clear to auscultation. The heart was regular, with normal first and second heart sounds. Abdominal examination was normal. The extremities were without clubbing, cyanosis or edema. Neurologic examination was normal.

A chest radiograph demonstrated multiple small nodules throughout the upper and lower lung fields bilaterally. A chest CT scan showed multiple, well circumscribed nodules measuring 3 to 5 mm in diameter. No other significant abnormalities were noted. Pulmonary function studies were normal.

Video-assisted thoracoscopic lung biopsy revealed multiple, well-demarcated nodules composed of slightly thickened alveolar septa lined by hyperplastic type II pneumocytes; mild cytologic atypia was noted. HMB-45 stains were negative, and tuberin immunoreactivity in the nodules was positive. The findings are consistent with a diagnosis of multifocal micronodular pneumocyte hyperplasia (MNPH).

Discussion: Tuberous sclerosis (TSC) is a rare disorder characterized by mental retardation, seizures, and hamartomatous proliferations involving the skin, kidneys, and brain. Familial and sporadic cases have been described. Pulmonary involvement, which occurs in fewer than 3% of patients, is usually clinically indistinguishable from lymphangioleiomyomatosis (LAM). MNPH is a newly-recognized, rare pulmonary manifestation of TSC. MNPH may occur in concert with LAM or, as in this case, occur alone. The clinical significance of MNPH is uncertain. However, the prognosis does not appear to be as severe as in LAM based on case series. MNPH may represent a forme frust of TSC or, alternatively, be part of the spectrum of LAM.

Conclusion: MNPH is a newly-recognized pulmonary manifestation of TSC, which appears to have less impact than LAM on patients' clinical course.

J. D. Christie, MD and M. A. Grippi, MD--University of Pennsylvania Health System, Philadelphia, PA

COPYRIGHT 1999 American College of Chest Physicians
COPYRIGHT 2000 Gale Group

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