The value of investigation for genetic counselling in tuberous sclerosis

Tuberous sclerosis--a multi system disease

Tuberous sclerosis is a genetic disease with autosomal dominant inheritance, associated with hamartomas in several organs and various skin findings. A case of a ten year old boy is presented here to highlight the multisystem involvement in tuberous sclerosis. The child had seizures, facial papular naevi and peri-ungual fibromas. MRI revealed cortical tubers, white matter lesions and subependymal nodules. Orbital ultrasound showed retinal hamartoma on the left side. Ultrasound of the abdomen revealed a soft tissue mass at the upper pole of left kidney with a small cyst in right kidney.

Tuberous sclerosis

Tuberous sclerosis is a serious inherited disease which poses major challenges for affected families and those caring for them. Identification of the genes causing the condition and study of their protein products has shed light on the pathogenesis of the disease and provided valuable new information about signalling pathways regulating protein synthesis and cell growth. There is now the exciting possibility of drug therapy for some of the manifestations of the disease.

Specific Genetic Disorders and Autism: Clinical Contribution Towards their Identification

Autism is a heterogeneous disorder that can reveal a specific genetic disease. This paper describes several genetic diseases consistently associated with autism (fragile X, tuberous sclerosis, Angelman syndrome, duplication of 15q11-q13, Down syndrome, San Filippo syndrome, MECP2 related disorders, phenylketonuria, Smith-Magenis syndrome, 22q13 deletion, adenylosuccinate lyase deficiency, Cohen syndrome, and Smith-Lemli-Opitz syndrome) and proposes a consensual and economic diagnostic strategy to help practitioners to identify them. A rigorous initial clinical screening is presented to avoid unnecessary laboratory and imaging studies. Regarding psychiatric nosography, the concept of "syndromal autism"--autism associated with other clinical signs should be promoted because it may help to distinguish patients who warrant a multidisciplinary approach and further investigation.

[Post mortem brain MRI: an alternative for pathology examination in Bourneville tuberous sclerosis of the fetus?]

Antenatal discovery of cardiac rhabdomyomes evokes the diagnosis of Bourneville's disease. Antenatal brain exploration with ultrasonography and magnetic resonance imaging (MRI) can highlight cerebral localizations. In the event of termination of pregnancy, confirmation of the cerebral lesions can be achieved with post mortem MRI as well as pathology examination. MRI can be usefully employed in the event pathology examination is not feasible.

Fetal cardiac anomalies and genetic syndromes

Cardiac anomalies may occur in isolation or can be part of a genetic syndrome. In this article, we describe some of the genetic syndromes commonly associated with cardiac anomalies where there are other sonographic features that may aid accurate prenatal diagnosis.

Prevalence of hypopigmented macules in a healthy population

OBJECTIVE

Although hypopigmented macules are an important manifestation of tuberous sclerosis (TS), the probability of TS in healthy individuals who have hypopigmented macules is unknown. The purpose of this study was to establish the prevalence of hypopigmented macules among a cross section of the general white population.

STUDY DESIGN

The skin of 423 white individuals younger than 45 years of age was screened for hypopigmented macules with ambient incandescent and fluorescent light and a Wood lamp. Indirect ophthalmoscopy was performed in patients with unexplained hypopigmentation to screen for retinal manifestations of TS.

RESULTS

Twenty individuals (4.7%) had at least one hypopigmented macule. Of these, four had more than one macule. None had more than three. Two (8%) of the 25 hypopigmented macules were identified only with a Wood lamp. Indirect ophthalmoscopy was performed in 13 (65%) of these 20 individuals. None showed the retinal findings of TS.

CONCLUSIONS

The prevalence of hypopigmented macules in the general population has been underestimated. The presence of a few hypopigmented macules on the skin of an otherwise healthy individual without a family history of TS need not prompt an evaluation to rule out this disorder.

Hypopigmented skin alterations resembling tuberous sclerosis in normal skin

The significance of hypopigmented skin findings as manifestations of the gene for tuberous sclerosis (TS) in near relatives of TS patients is a difficult problem. We therefore studied the number and kind of whitish skin alterations found in 100 medical students and 100 school children. Ninety three percent of the former and 79% of the latter had some whitish lesions, many of them scars. Twenty percent of the adults and 12% of the children had roundish or oval macules larger than 10 mm in diameter, not known to be scars. In clinical practice with TS patients, our attention has been drawn to whitish raised masses or streaks in their first degree relatives. These were also found in study subjects so the significance of such lesions remains unclear. The role of Wood's light turned out to be questionable, far from pathognomonic for TS; 25% of all the whitish findings and 53% of the hypopigmented macules larger than 10 mm in diameter showed distinct or brilliant fluorescence under Wood's light.

Neurocutaneous syndromes associated with pigmentary skin lesions

Tremendous strides have been made in our understanding of genetic disorders, including those that involve both the skin and the nervous system. The list of well-established neurocutaneous syndromes has increased during a few decades from a few classical phakomatoses to more than 30 entities. The dermatologist has the opportunity to facilitate precise diagnosis and optimal care for these patients by recognition of the cutaneous markers for these diseases. We have attempted to provide an overview of some recent advances in those syndromes manifested by pigmentary skin changes, emphasizing the clinical spectrum of each disorder and providing guidelines for an approach to management.

Renal involvement in tuberous sclerosis complex: a retrospective survey

In a retrospective survey performed in Germany and Switzerland, 207 patients (ranging in age from newborn to 70 years) were evaluated in order to establish the frequency, prognosis and diagnostic awareness of kidney involvement in the tuberous sclerosis complex. Renal manifestations were observed in 48% of patients: renal cysts (33 patients), renal angiomyolipoma (AML) (30 patients), a combination of both (8 patients), renal cell carcinoma (3 patients), life-threatening events such as haemorrhage (4 patients), hypertensive crisis (2 patients) and chronic renal failure (10 patients) were also documented. The diagnostic imaging techniques of ultrasonography, intravenous urography, computed tomography and magnetic resonance imaging (MRI) are important but do not always yield definitive information. Differentiation between AML and cysts can be achieved using special MRI techniques (RARE). The potential for renal involvement should be monitored in all patients with the tuberous sclerosis complex.

Identification and characterization of the tuberous sclerosis gene on chromosome 16

Tuberous sclerosis (TSC) is an autosomal dominant multisystem disorder with loci assigned to chromosomes 9 and 16. Using pulsed-field gel electrophoresis (PFGE), we identified five TSC-associated deletions at 16p13.3. These were mapped to a 120 kb region that was cloned in cosmids and from which four genes were isolated. One gene, designated TSC2, was interrupted by all five PFGE deletions, and closer examination revealed several intragenic mutations, including one de novo deletion. In this case, Northern blot analysis identified a shortened transcript, while reduced expression was observed in another TSC family, confirming TSC2 as the chromosome 16 TSC gene. The 5.5 kb TSC2 transcript is widely expressed, and its protein product, tuberin, has a region of homology to the GTPase-activating protein GAP3.

Variability of expression in tuberous sclerosis

We present three families in whom a diagnosis of tuberous sclerosis is difficult to secure and we review published reports about similar cases. Tuberous sclerosis has been reported to affect as many as 1 in 9400 subjects in the population. The manifestations of this disease vary not only between but also within families. Currently no reliable method of prenatal diagnosis is available. For these reasons, subjects known to be at 50% risk should be assessed scrupulously to clarify their status. These cases illustrate the difficulties in the clinical diagnosis of tuberous sclerosis and further reinforce the need for a molecular method of determining whether an at risk subject has the disease.

Tuberous sclerosis complex: genetic aspects

Much has been learned about tuberous sclerosis complex (TSC) since it was described at the end of the nineteenth century. TSC was recognized to be a genetic disease with autosomal dominant inheritance in the early twentieth century. The prevalence in the general population is at least 1 in 10,000 with two-thirds of cases occurring sporadically and one-third of cases being familial. The disease exhibits variable expression which may cause mildly affected individuals to be undiagnosed. Because the aberrant or missing proteins which result in TSC have eluded investigators, a positional cloning approach has been pursued to find the mutated genes. Genetic linkages have been reported to chromosomes 9, 11, and 12. There is definite evidence for a TSC-causing locus on chromosome 9 which is thought to account for between one-third and one-half of all familial cases. Investigators have narrowed the location on chromosome 9 to approximately two megabases of physical distance. There is some evidence for a locus on chromosome 11 which probably accounts only for a small percentage of familial cases. The locus proposed on chromosome 12 was reported by a single group and has not been confirmed by other research groups. Evidence for genetic heterogeneity is abundant. There is definitely a TSC-causing locus on chromosome 9q (TSC-1) and there is at least one additional locus, maybe more than one. As the molecular basis of TSC unfolds, new insight will be gained about the protean nature of the disorder and the genetic heterogeneity.

Neurocutaneous syndromes

Many of the neurocutaneous disorders are more common than once suspected, in part because patients with milder forms of the disorders are now more likely to be recognized. Improved diagnostic studies and increasingly specific medical and surgical therapy allow some previously untreatable complications to be successfully managed. Genetic linkage analysis has localized the abnormal gene for some of the hereditary neurocutaneous disorders onto specific chromosomes, and newly developed clinical diagnostic criteria have improved our ability to establish a definite diagnosis in less obvious patients. Thus, the outlook for these patients is no longer uniformly pessimistic.

Echocardiography and genetic counselling in tuberous sclerosis

OBJECTIVE

To assess echocardiography as an investigation for the detection of occult gene carriers in tuberous sclerosis.

PATIENTS

Sixty parents of children with tuberous sclerosis who had been extensively investigated for signs of the disease and 60 age and sex matched controls.

PROCEDURE

Blind study by two experienced echocardiographers and blind interpretation of video recordings by an adult cardiologist.

SETTING

Cardiology department of a district general hospital.

RESULTS

Two parents and three controls had bright echodense areas interpreted as possible rhabdomyomas.

CONCLUSIONS

In our hands echocardiography of adults is not an investigation with a high specificity for gene detection in tuberous sclerosis.

Non-penetrance in tuberous sclerosis

Non-penetrance has not been reported in tuberous sclerosis when modern non-invasive investigations have been performed. We report a four generation family in which there was a subject with minimal expression and another with non-penetrance between a great grandfather and his great grandson. This situation highlights the need for full investigation of children of tuberous sclerosis patients before counselling a low recurrence risk for the disease.

Two unusual tumours of the gastrointestinal tract in a patient with tuberous sclerosis

A 16 year old girl with an established diagnosis of tuberous sclerosis presented with a 1 year history of swelling of the left cheek. A 2 cm diameter tumour was excised which showed histological features of a solid variant of a minor salivary gland basal cell adenoma. One year later during laparotomy and excision of multiple renal angiomyolipomas, a 5 cm diameter subserosal tumour was found at the hepatic flexure of the colon. Examination of biopsy material revealed a leiomyoma. This case is presented to demonstrate two tumours that have not to the authors' knowledge been previously described in a young patient with tuberous sclerosis. Although the association may be coincidental, these tumours could represent two rare associations of tuberous sclerosis.

Tuberous sclerosis in two sibs of normal parents

We report on a family with two sibs suffering from tuberous sclerosis. The parents were normal in all clinical tests including Wood's light examination of the skin, ophthalmoscopy, X-ray computerized tomography of brain, liver, and kidneys, cardiac echography and MR imaging of the brain. The most likely explanation is a germinal cell mosaic in one of the parents. A recurrence risk of 20 to 37% seems appropriate. The implications for risk assessment of sporadic cases are emphasized.