Genetic heterogeneity in tuberous sclerosis: phenotypic correlations.

There is increasing evidence for genetic heterogeneity in tuberous sclerosis (TSC) on the basis of linkage analysis in affected kindreds. We have performed a detailed assessment of an affected South African family in which there is no evidence of linkage to chromosome 9 markers. The affected persons have atypical clinical features, namely prominent nuchal skin tags, a confetti pattern of hypopigmentation of the skin of the lower legs, and absence of ungual fibromata. Further investigation of these unusual phenotypic features is warranted in order to determine whether these lesions are consistently present in families in whom the gene for TSC is not on 9q34. We conclude that confetti depigmentation and nuchal skin tags may be clinical pointers to an alternative locus for TSC.     

Evidence for genetic heterogeneity in tuberous sclerosis.

The question of genetic heterogeneity in tuberous sclerosis (TSC) was addressed by genetic linkage studies in eight affected families using nine polymorphic markers (EFD126.3, MCT136, ABO, ABL, AK1, and MCOA12 from distal 9q, and PBGD, MCT128.1, and 1CJ52.208M from distal 11q). The data as a whole supported a TSC locus on distal 9q, the peak lod score on multipoint analysis being 3.77 at 6 cM proximal to the Abelson oncogene locus (ABL). However, analysis of two point lod scores using the HOMOG programs showed significant evidence for genetic heterogeneity (p = 0.01), linkage to ABL being unlikely in one family. After exclusion of the unlinked family, multipoint analysis gave a peak lod score of 6.1 in the vicinity of ABL. The family unlinked to ABL showed no recombinants with two chromosome 11 probes, but was too small to provide significant evidence for linkage. Genetic heterogeneity in TSC will complicate efforts to clone the causative genes and severely limit the use of linked probes for carrier detection and prenatal diagnosis.     

Three independent mutations in the TSC2 gene in a family with tuberous sclerosis

Tuberous sclerosis complex (TSC) is a rare autosomal dominant disorder characterized by hamartomas and hamartias in multiple organs. TSC is caused by a wide spectrum of mutations within the TSC1 and TSC2 genes. Here, we report a unique family with three independent pathological mutations in TSC2. A c.1322G>A mutation in exon 12 created a stop codon, whereas a second mutation in exon 23 (c.2713C>T) was a missense change. The third mutation was a 4 base pair deletion in intron 20 of TSC2. We showed that this mutation was responsible for abnormal splicing. The three mutations were most likely de novo, as parents of affected patients did not present any features of TSC. In addition, we showed gonadal mosaicism in a branch of the family. To our knowledge, several independent mutations in TSC2 have never been observed in a single family. The probability of finding a family with three different pathological TSC2 mutations is extremely low. We discuss two main hypotheses that may be raised to explain this recurrence: (i) the TSC2 mutation rate is underestimated. In such a case, the likelihood of finding a family with three independent mutations in TSC2 may not be dramatically low; (ii) a heritable defect in a DNA repair gene (eg, mismatch repair gene) segregating in the family that is unlinked to the TSC2 gene might predispose to the occurrence of multiple TSC2 gene mutations, used as a specific target during embryogenesis.     

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.     

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.     

Leiomyomatosis-like lymphangioleiomyomatosis of the colon in a female with tuberous sclerosis.

Smooth muscle lesions of the large bowel, excluding the rectum, are generally rare, and diffuse smooth muscle lesions, termed leiomyomatosis, are even rarer. In this report, we document, for the first time, leiomyomatosis-like lymphangioleiomyomatosis (LAM) of the ascending, transverse, and descending colon in association with bilateral renal angiomyolipoma (AML) in a 30-year-old Chinese female with tuberous sclerosis complex (TSC). She presented with protracted constipation for which a colectomy was performed. Histology disclosed multiple confluent nodular CD34 and CD117 negative smooth muscle proliferation within the large bowel wall, whereas the renal biopsy revealed typical features of AML. Interestingly, the epithelioid smooth muscle cells of both the colonic and renal lesions were HMB45 positive, suggesting that leiomyomatosis-like LAM of the colon, pulmonary LAM and AML are closely related entities. The patient remained free of complications for the last five years after surgery. Leiomyomatosis-like LAM of the large bowel probably represents another manifestation of the tendency of TSC to be associated with proliferative lesions.     

Cloning and evaluation of RALGDS as a candidate for the tuberous sclerosis gene TSC1

RALGDS is a 115 kDa protein which was identified by its ability to enhance guanine nucleotide exchange for the ras family member ral . It also binds to activated ras and rap1 , and appears to function as part of a signalling complex in downstream events following rap1 activation. Here we report the identification of full-length cDNA clones for human RALGDS, isolated from a brain cDNA library. The predicted protein has strong sequence homology to rat and murine isoforms of RALGDS in the N- and C-terminal regions, but an internal region (aa 250–380) shows relatively high divergence with only 42% identical amino acid residues. The human RALGDS gene is contained within a 30 kb region of 9q34, approximately 200 kb proximal to the ABO gene, within the current critical region for the tuberous sclerosis gene TSC1. Partial genomic structure was determined; it consists of at least 11 exons. Based upon analysis of Southern blots from 110 TSC patients, genomic DNA SSCP analysis, and RT-PCR analysis which demonstrated RNA expression of both alleles in patients from 9q34-linked TSC families using intragenic polymorphisms, we conclude that RALGDS is not likely to be TSC1.     

Nail-patella syndrome in an Indian family: clinical and linkage data

Of 11 persons found to have the nail-patella syndrome in an Indian family, two show malposition of teeth of a marked but unspecific nature. It will be difficult to determine whether this feature is one more effect of the nail-patella allele. The linkage estimate for the nail-patella and ABO loci (1 recombinant in 16 meiotic products) is consistent with estimates in families of European origin. The author is grateful to the members in the pedigree who so willingly offered themselves for the investigation. Thanks are also due to Mi D. Roy Choudhry, Deputy Keeper (Anthropology), National Museum, New Delhi, for his help during the study.     

Familial cylindromatosis mimicking tuberous sclerosis complex and confirmation of the cylindromatosis locus, CYLD1, in a large family.

A large Dutch family had been known for many years to be affected with skin tumours labelled as adenoma sebaceum, which were inherited in an autosomal dominant fashion. Since this skin sign is considered pathognomonic for tuberous sclerosis complex, the condition in the family was labelled accordingly, in the absence of further clinical features of tuberous sclerosis complex-like mental retardation or epilepsy. The skin changes started at early puberty with small eruptions around the nose and progressed to larger tumours, with considerable variation in severity. Some affected members had required plastic surgical reconstruction following excision. Linkage analysis in this family was performed for the two chromosomal regions involved in tuberous sclerosis complex on chromosomes 9q34 and 16p13, but no positive linkage was found. On critical re-evaluation of the clinical and pathological data and renewed assessment, the working diagnosis was changed to autosomal dominant cylindromatosis. The recently published candidate region for cylindromatosis on chromosome 16q12-13 was subsequently proven to be positively linked with a lod score of 3.02 with marker D16S308. Review of pathological specimens confirmed the diagnosis of cylindromatosis. DNA analysis of tumour tissue showed loss of heterozygosity for the cylindromatosis CYLD1 locus. These results confirm the candidate locus for cylindromatosis on chromosome 16q12-13.     

Dissociate expression of tuberous sclerosis complex 1 product hamartin in a skin and pulmonary lesion of a tuberous sclerosis complex

Tuberous sclerosis complex is a multisystemic disorder characterized by systemic hamartomas. Tuberous sclerosis complex is caused by the mutation of tumor suppressor genes tuberous sclerosis complex 1 or tuberous sclerosis complex 2. Tuberous sclerosis complex tumorigenesis is not always accompanied by loss of heterozygosity. The incidence of loss of heterozygosity is varied among the organs in which hamartomas occur. We report a 25-year-old woman diagnosed with tuberous sclerosis complex with lymphangiomyomatosis. Expression of tuberin and hamartin was examined in lung and skin specimens. Her skin lesion (angiofibroma) expressed both hamartin and tuberin, but her pulmonary lesion did not express hamartin. This suggests that different mechanisms of tumorigenesis may occur in pulmonary and skin lesions.     

Loss of heterozygosity in tuberous sclerosis hamartomas.

We have previously described in tuberous sclerosis (TSC) hamartomas the phenomenon of loss of heterozygosity (LOH) for DNA markers in the region of both the TSC2 gene on chromosome 16p13.3 and the TSC1 gene on 9q34. We now describe the spectrum of LOH in 51 TSC hamartomas from 34 cases of TSC. DNA was extracted from leucocytes or normal paraffin embedded tissue, and from frozen paraffin embedded hamartoma tissue from the same patient. The samples were analysed for 11 markers spanning the TSC1 locus and nine markers spanning the TSC2 locus. Twenty-one of 51 hamartomas showed LOH (41%). There was significantly more LOH on 16p13.3, with 16 hamartomas showing LOH around TSC2, and five in the vicinity of TSC1. No hamartoma showed LOH for markers around both loci. All the areas of LOH on chromosome 9 were large, but the smallest region of overlap lay between the markers D9S149 and D9S114, providing independent evidence for the localisation of the TSC1 gene. These data show that LOH is a common finding in a wide range of hamartomas, affecting the same TSC locus in different lesions from the same patient but not affecting both loci. These data support the hypothesis that both the TSC genes act as tumour suppressors and that the manifestations of TSC in patients with germline TSC mutations rise from "second hit" somatic mutations inactivating the remaining normal copy of the TSC gene.     

HLA class II-associated genetic susceptibility in multiple sclerosis: a critical evaluation

Multiple sclerosis (MS) has, since the 1970s, been known to be associated with the HLA-Dw2 and -DR2 specificities in Caucasian Europeans and North Americans. By the use of genomic typing techniques, the association has been specified to be with the DRw15,DQw6,Dw2, i.e. the DRB1*1501-DQA1*0102-DQB1*0602 haplotype. A significant DPw4 association in Scandinavian MS patients has been described in one report. However, this association has not been confirmed in several subsequent studies with patients from the same and other ethnic groups. During the last few years several reports, based on serological, RFLP and PCR-SSO data, have suggested that the HLA class II-associated MS susceptibility gene(s) may be more closely associated with the DQ than with the DR subregion. The observations that the HLA-DQB1 genes of MS patients share long stretches of sequence motifs and also carry DQA1 alleles encoding glutamine at position 34 of the DQ alpha chain have received considerable attention. It has been suggested that the susceptibility to develop MS might be determined by the corresponding DQ alpha-beta heterodimers either encoded in cis or in trans. We have investigated these issues in a large group of Swedish MS patients (n = 179). We found that the associations with the suggested DQB1 sequences and position 34 of the DQ alpha chain were due to linkage disequilibrium and secondary to the association with the DRw15,DQw6,Dw2 haplotype (p less than 10(-9) and p less than 10(-8), respectively). No overrepresentation of the implicated DQ alpha-beta heterodimers was observed in DRw15,DQw6,Dw2-negative patients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phenotypic variation of tuberous sclerosis in a single extended kindred.

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder with a great degree of phenotypic variability. Given the presence of two gene loci underlying this disorder, locus heterogeneity may account for some of the variability. However, significant within family variation suggests that different genes do not explain the majority of this variation. The purpose of this research is to identify physical and behavioural variation in expression of TSC in a single large extended kindred. TSC in this kindred is cosegregating with markers localised to chromosome 16p13.3. The expression of TSC in this kindred is quite variable with a substantial proportion of persons showing very mild physical expression of TSC. In contrast to very mild physical expression of TSC in some family members, there is a significant clustering of psychiatric disorders among persons affected with TSC compared to their unaffected relatives. This finding, coupled with the mild physical expression of TSC in some family members, supports a hypothesis that the TSC2 gene may present phenotypically as mild skin signs and significant behavioural problems.     

X-linkage and genetic heterogeneity in bipolar-related major affective illness: reanalysis of linkage data

It has been suggested that an X-linked dominant allele operates in the genetic transmission of bipolar (manic-depressive) illness. Linkage studies with X-chromosome markers have remained inconclusive, showing both positive and negative results. Some of the ambiguity may be attributed to imprecise analytic methods and genetic heterogeneity. In this report, recently published pedigree series are reanalysed for linkage using a systematic method of pedigree analysis (Liped 3) with an accurate age-of-onset correction. Linkage heterogeneity is assessed through a two-recombination fraction heterogeneity test suggested by Smith (1963). The results are as follows: (1) Close linkage of bipolar illness to colourblindness (deutan and protan) and glucose-6-phosphate dehydrogenase deficiency appears to be present in some pedigrees, with estimated recombination fractions of θ= 0.05 and 0.00, respectively; (2) Linkage with the Xg blood group cannot be supported. These results are consistent with known linkages on the X chromosome.     

Glioblastoma multiforme with tuberous sclerosis. Report of a case

Gliomas of the CNS associated with tuberous sclerosis have been well documented; malignant degeneration to glioblastoma multiforme, however, is rare. We studied a 17-year-old boy with stigmata of tuberous sclerosis and a cerebral glioblastoma multiforme. The rarity of this occurrence suggests that neoplasms arising from hamartomas may behave differently than those CNS tumors that arise apparently de novo.     

Autosomal dominant Polycystic Kidney Disease: A linkage evaluation of heterogeneity in Italy

A survey of 29 families with Adult Polycystic Kidney Disease (ADPKD) was performed to evaluate the genetic heterogeneity of the disease in Italy. The approach was through the linkage between the disease and 2 polymorphic DNA fragments as detected by the probes 3′HVR and 24.1. Linkage between the polymorphic markers and the disease was confirmed, with the following lod scores: between 3′HVR and ADPKD1 = 12.974 at θ = 0.02; between 24.1 and ADPKD = 1.716 at θ = 0.07; between 3′HVR and 24.1 = 2.738 at θ = 0.09. No evidence of significant genetic heterogeneity in the examined Italian regions was detected.     

Multifocal renal cell carcinoma in sibs from a chromosome 9 linked (TSC1) tuberous sclerosis family.

Multifocal renal cell carcinomas (RCCs), together with angiomyolipomas (AMLs) and renal cysts, were identified in early adult life in two sisters with tuberous sclerosis (TSC). They were members of a multigenerational tuberous sclerosis family showing strong evidence for a mutant TSC causing gene on chromosome 9 (TSC1). Previous reports of multifocal RCC in young patients with TSC suggest that constitutional mutations at the TSC loci may predispose to RCC. In the rat a germline mutation affecting the TSC2 gene is associated with transmission of multifocal RCC as an autosomal dominant trait. However, the cases reported here are the first to suggest a similar role for the TSC1 gene in renal cell carcinogenesis.