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D J Halley

Publications and source records attributed to D J Halley.

At least 19 recordsLinked to original sources

Differential localization of hamartin and tuberin and increased S6 phosphorylation in a tuber.

In a tuberous sclerosis patient with a mutation in the TSC1 tumor suppressor gene, no second-hit mutation was found in a resected cortical tuber. Tuber giant cells showed predominantly nuclear hamartin, cytosolic tuberin, and hyperphosphorylation of S6. Differential accumulation of hamartin and tuberin in separate cellular compartments of giant cells may prevent formation of the hamartin-tuberin complex, resulting in increased S6 phosphorylation. These data provide an alternative mechanism for tuberogenesis.

Cerebral Cortex↗

[From gene to disease; Krabbe disease and galactosylceramidase deficiency].

Krabbe disease is a devastating lysosomal storage disease with autosomal recessive inheritance. Early symptoms of leukodystrophy, such as irritability and hypertonicity, appear at 3 to 6 months of age, but progress rapidly to severe mental and motor deterioration and death in the second year. The disease is caused by the deficiency of the lysosomal enzyme galactosylceramidase, which is in turn caused by mutations in the GALC gene. The incidence of the infantile form of the disease in the Netherlands is estimated at 1.3 per 100,000 births; 50% of the patients' alleles show the large 30-kb deletion. Early diagnosis by enzyme assay in leukocytes or skin fibroblasts permits timely genetic counselling and prenatal diagnosis, which is reliably made by enzyme or mutation analysis in the chorionic villi.

Galactosylceramidase↗

TSC2 missense mutations inhibit tuberin phosphorylation and prevent formation of the tuberin-hamartin complex.

Tuberous sclerosis (TSC) is an autosomal dominant disorder characterized by a broad phenotypic spectrum that includes seizures, mental retardation, renal dysfunction and dermatological abnormalities. Inactivating mutations to either of the TSC1 and TSC2 tumour suppressor genes are responsible for the disease. TSC1 and TSC2 encode two large novel proteins called hamartin and tuberin, respectively. Hamartin and tuberin interact directly with each other and it has been reported that tuberin may act as a chaperone, preventing hamartin self-aggregation and maintaining the tuberin-hamartin complex in a soluble form. In this study, the ability of tuberin to act as a chaperone for hamartin was used to investigate the tuberin-hamartin interaction in more detail. A domain within tuberin necessary for the chaperone function was identified, and the effects of TSC2 missense mutations on the tuberin-hamartin interaction were investigated to allow specific residues within the central domain of tuberin that are important for the interaction with hamartin to be pin-pointed. In addition, the results confirm that phosphorylation may play an important role in the formation of the tuberin-hamartin complex. Although mutations that prevent tuberin tyrosine phosphorylation also inhibit tuberin-hamartin binding and the chaperone function, our results indicate that only hamartin is phosphorylated in the tuberin-hamartin complex.

Amino Acid Substitution↗

[From gene to disease; androgen receptor gene, androgen insensitivity syndrome, and spinal and bulbar muscle atrophy].

Androgen insensitivity is an X-linked disorder of male sexual differentiation resulting from a defective androgen receptor. Spinal and bulbar muscular atrophy (Kennedy's disease) is an X-linked disease, resulting from expansion of the polyglutamine stretch in the N-terminal part of the androgen receptor. Mutation analysis confirms the clinical diagnosis of androgen insensitivity and enables carrier detection and prenatal diagnosis. Kennedy's disease, with its diagnostic problem of clinical variability, is diagnosed or excluded when an expanded CAG-repeat is present or absent in exon 1 of the androgen receptor. Molecular testing can be used for carrier detection and genetic counselling.

Androgen-Insensitivity Syndrome↗

[From gene to disease; TSC1 and TSC2 genes and tuberous sclerosis complex].

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterised by the presence of multiple hamartomas in different parts of the body: the skin, central nervous system, retina, heart, and kidneys. The diagnosis is based on clinical criteria. Screening for TSC must include investigation of skin, CT-scan of the brain and retinal examination. Mutations in TSC patients are present in either the TSC1 or the TSC2 gene. Due to the complexity of the genes and the observation that almost each family has a unique mutation, DNA analysis is not suitable for fast diagnosis of the index patient, but may be used for testing relatives at risk.

Diagnosis, Differential↗

Large regional differences in the frequency of distinct BRCA1/BRCA2 mutations in 517 Dutch breast and/or ovarian cancer families.

In 517 Dutch families at a family cancer clinic, we screened for BRCA1/2 alterations using the Protein Truncation Test (PTT) covering approximately 60% of the coding sequences of both genes and direct testing for a number of previously identified Dutch recurrent mutations. In 119 (23%) of the 517 families, we detected a mutation in BRCA1 (n=98; 19%) or BRCA2 (n=21; 4%). BRCA1/2 mutations were found in 72 (52%) of 138 families with breast and ovarian cancer (HBOC), in 43 (13%) of the 339 families with breast cancer only (HBC), in 4 (36%) of 11 families with ovarian cancer only (HOC), and in nine of 29 families with one single young case (<40 years) of breast cancer. Between the different subgroups of families (subdivided by the number of patients, cancer phenotype and age of onset) the proportion of BRCA1/2 mutations detected, varied between 6 and 82%. Eight different mutations, each encountered in at least six distinct families, represented as much as 61% (73/119 families) of all mutations found. The original birthplaces of the ancestors of carriers of these eight recurrent mutations were traced. To estimate the relative contribution of two important regional recurrent mutations (BRCA1 founder mutation IVS12-1643del3835 and BRCA2 founder mutation 5579insA) to the overall occurrence of breast cancer, we performed a population-based study in two specific small regions. The two region-specific BRCA1 and BRCA2 founder mutations were detected in 2.8% (3/106) and 3.2% (3/93) of the unselected breast tumours, respectively. Of tumours diagnosed before the age of 50 years, 6.9% (3/43) and 6.6% (2/30) carried the region-specific founder mutation. Thus, large regional differences exist in the prevalence of certain specific BRCA1/BRCA2 founder mutations, even in very small areas concerning populations of approximately 200000 inhabitants.

Adult↗

Analysis of TSC2 stop codon variants found in tuberous sclerosis patients.

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by mutations to the TSC1 and TSC2 tumour suppressor genes. We detected two sequence changes involving the TSC2 stop codon and investigated the effects of these changes on the expression of tuberin, the TSC2 gene product, and on the binding between tuberin and the TSC1 gene product, hamartin. While elongation of the tuberin open reading frame by 17 amino acids did not interfere with tuberin-hamartin binding, a longer extension prevented this interaction. Our data illustrate how functional protein assays can assist in the verification and characterisation of disease-causing mutations.

Animals↗

Chloride conductance and genetic background modulate the cystic fibrosis phenotype of Delta F508 homozygous twins and siblings.

To investigate the impact of chloride (Cl(-)) permeability, mediated by residual activity of the cystic fibrosis transmembrane conductance regulator (CFTR) or by other Cl(-) channels, on the manifestations of cystic fibrosis (CF), we determined Cl(-) transport properties of the respiratory and intestinal tracts in Delta F508 homozygous twins and siblings. In the majority of patients, cAMP and/or Ca(2+)-regulated Cl(-) conductance was detected in the airways and intestine. Our finding of cAMP-mediated Cl(-) conductance suggests that, in vivo, at least some Delta F508 CFTR can reach the plasma membrane and affect Cl(-) permeability. In respiratory tissue, the expression of basal CFTR-mediated Cl(-) conductance, demonstrated by 30% of Delta F508 homozygotes, was identified as a positive predictor of milder CF disease. In intestinal tissue, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid-insensitive (DIDS-insensitive) Cl(-) secretion, which is indicative of functional CFTR channels, correlated with a milder phenotype, whereas DIDS-sensitive Cl(-) secretion was observed mainly in more severely affected patients. The more concordant Cl(-) secretory patterns within monozygous twins compared with dizygous pairs imply that genes other than CFTR significantly influence the manifestation of the basic defect.

Adolescent↗

The tuberous sclerosis-1 (TSC1) gene product hamartin suppresses cell growth and augments the expression of the TSC2 product tuberin by inhibiting its ubiquitination.

We report here that overexpression of the tuberous sclerosis-1 (TSC1) gene product hamartin results in the inhibition of growth, as well as changes in cell morphology. Growth inhibition was associated with an increase in the endogenous level of the product of the tuberous sclerosis-2 (TSC2) gene, tuberin. As overexpression of tuberin inhibits cell growth, and hamartin is known to bind tuberin, these results suggested that hamartin stabilizes tuberin and this contributes to the inhibition of cell growth. Indeed, transient transfection of TSC1 increased the endogenous level of tuberin, and transient co-transfection of TSC1 with TSC2 resulted in higher tuberin levels. The stabilization was explained by the finding that tuberin is highly ubiquitinated in cells, while the fraction of tuberin that is bound to hamartin is not ubiquitinated. Co-expression of tuberin stabilized hamartin, which is weakly ubiquitinated, in transiently transfected cells. The amino-terminal two-thirds of tuberin was responsible for its ubiquitination and for stabilization of hamartin. A mutant of tuberin from a patient missense mutation of TSC2 was also highly ubiquitinated, and was unable to stabilize hamartin. We conclude that hamartin is a growth inhibitory protein whose biological effect is likely dependent on its interaction with tuberin.

Animals↗

Residual chloride secretion in intestinal tissue of deltaF508 homozygous twins and siblings with cystic fibrosis. The European CF Twin and Sibling Study Consortium.

BACKGROUND & AIMS: Cholinergic stimulation of chloride secretion is impaired in the intestines of patients with cystic fibrosis (CF). However, intestinal chloride secretion has been observed in patients with mild CF mutations. The aim of this study was to investigate residual Cl(-) secretion in the intestine of DeltaF508 homozygous CF patients, and examine the contribution of cystic fibrosis transmembrane conductance regulator (CFTR) and alternative Cl(-) conductances. Twins and siblings with identical CFTR genotypes were investigated to determine the impact of factors other than CFTR on chloride secretion. METHODS: Chloride secretion in rectal tissue was investigated by applying Ca(2+) and adenosine 3',5'-cyclic monophosphate (cAMP)-linked agonists before and after the inhibition of alternative Cl(-) conductances with 4,4'-diisothiocyanostilbene-2, 2'-disulfonic acid (DIDS). RESULTS: cAMP-mediated Cl(-) secretion was observed in 73% of patients, and 20% showed DIDS-sensitive Ca(2+)-activated Cl(-) secretion. This DIDS-sensitive alternative chloride conductance was seen only in CF patients who also responded to cAMP agonists. Chloride secretion was more concordant within monozygous twins than within dizygous pairs. CONCLUSIONS: These results suggest the presence of CFTR-mediated Cl(-) secretion in a subgroup of patients, implying that a portion of deltaF508 CFTR can be processed in vivo and function as a chloride channel in the apical membrane of intestinal cells. Moreover, a considerable number of deltaF508 homozygous patients express chloride conductances other than CFTR in their intestinal epithelia.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

An unbalanced submicroscopic translocation t(8;16)(q24.3;p13.3)pat associated with tuberous sclerosis complex, adult polycystic kidney disease, and hypomelanosis of Ito.

We report on a familial submicroscopic translocation involving chromosomes 8 and 16. The proband of the family had a clinical picture suggestive of a large deletion in the chromosome 16p13.3 area, as he was affected with tuberous sclerosis complex (TSC) and had alpha thalassaemia trait, and his half brother, who also had TSC, may have suffered additionally from polycystic kidney disease (PKD). FISH studies provided evidence for a familial translocation t(8;16)(q24.3;p13.3) with an unbalanced form in the proband and a balanced form in the father and in a paternal aunt. The unbalanced translocation caused the index patient to be deleted for the chromosome 16p13.3-pter region, with the most proximal breakpoint described to date for terminal 16p deletions. In addition, FISH analysis showed a duplication for the distal 8q region. Since the index patient also had hypomelanosis of Ito (HI), either of the chromosomal areas involved in the translocation may be a candidate region for an HI determining gene. Furthermore, it is noteworthy that both carriers of the balanced translocation showed a nodular goitre, while the proband has hypothyroidism.

Adult↗

Characterization of the cytosolic tuberin-hamartin complex. Tuberin is a cytosolic chaperone for hamartin.

Tuberous sclerosis (TSC) is an autosomal dominant disorder characterized by a broad phenotypic spectrum that includes seizures, mental retardation, renal dysfunction and dermatological abnormalities. Mutations to either the TSC1 or TSC2 gene are responsible for the disease. The TSC1 gene encodes hamartin, a 130-kDa protein without significant homology to other known mammalian proteins. Analysis of the amino acid sequence of tuberin, the 200-kDa product of the TSC2 gene, identified a region with limited homology to GTPase-activating proteins. Previously, we demonstrated direct binding between tuberin and hamartin. Here we investigate this interaction in more detail. We show that the complex is predominantly cytosolic and may contain additional, as yet uncharacterized components alongside tuberin and hamartin. Furthermore, because oligomerization of the hamartin carboxyl-terminal coiled coil domain was inhibited by the presence of tuberin, we propose that tuberin acts as a chaperone, preventing hamartin self-aggregation.

Animals↗

Prenatal detection of trisomy 18 caused by isochromosome 18p and 18q formation.

We report on the prenatal detection and further genetic studies in a case of trisomy 18 caused by isochromosome 18p [i(18p)] and 18q [i(18q)] formation. The diagnosis was made by standard cytogenetic techniques in amniotic fluid cells and confirmed by fluorescence in situ hybridization. The formation of the isochromosomes cannot be explained by a single model; centromere misdivision and meiosis II nondisjunction without recombination or mitotic misdivision are the most likely mechanisms of formation as indicated by DNA analysis.

Adult↗

Novel mutations in the LKB1/STK11 gene in Dutch Peutz-Jeghers families.

The Peutz-Jeghers syndrome (PJS) is a rare hereditary disorder in which gastrointestinal hamartomatous polyposis, mucocutaneous pigmentation, and a predisposition for developing cancer are transmitted in an autosomal dominant fashion. The recently identified LKB1/STK11 gene located at chromosome 19p13.3 is mutated in a number of PJS pedigrees. We performed mutation analysis in 19, predominantly Dutch, PJS families. In 12 of these families, we identified LKB1/STK11 mutations, none of which has been described before. These 12 novel LKB1/STK11 mutations consist of one nonsense mutation, three frameshift deletions, three frameshift insertions, two acceptor splice site mutations, and three missense mutations. In addition, we detected four polymorphisms in LKB1/STK11. In the remaining seven PJS families, we found no apparent abnormalities of the LKB1/STK1I gene, which could reflect the existence of locus heterogeneity in PJS. None of the mutations occurred in more than one family, and a number were demonstrated to have arisen de novo. The diverse array of mutations found, the apparent high mutation rate, as well as the existence of a possible second PJS locus, renders diagnostic or predictive genetic testing in individual patients difficult, although future identification of additional mutations or even gene(s) will help in increasing the yield of direct mutation analysis.

AMP-Activated Protein Kinase Kinases↗

Malignant pancreatic tumour within the spectrum of tuberous sclerosis complex in childhood.

UNLABELLED: A 12-year-old boy with tuberous sclerosis complex (TSC) presented with a large retroperitoneal tumour. Exploratory surgery revealed an infiltrative tumour originating from the pancreas, with local metastases to the lymph nodes. The histologal diagnosis was a malignant islet cell tumour. Retrospectively measured pancreatic hormone levels, however, were normal. A connection between the malignancy and TSC was demonstrated by loss of heterozygosity of the TSC2 gene in the tumour. The primary mutation Q478X in this patient was identified in exon 13 of the TSC2 gene on chromosome 16. CONCLUSION: Pancreatic islet cell tumours have been mainly associated with multiple endocrine neoplasia syndrome type 1. In our case we demonstrate a direct relationship of this tumour to tuberous sclerosis complex, in the absence of further signs of multiple endocrine neoplasia syndrome type 1.

Carcinoma, Islet Cell↗

High rate of mosaicism in tuberous sclerosis complex.

Six families with mosaicism are identified in a series of 62 unrelated families with a mutation in one of the two tuberous sclerosis complex (TSC) genes, TSC1 or TSC2. In five families, somatic mosaicism was present in a mildly affected parent of an index patient. In one family with clinically unaffected parents, gonadal mosaicism was detected after TSC was found in three children. The detection of mosaicism has consequences for genetic counseling of the families involved, as changed risks apply to individuals with mosaicism, both siblings and parents. Clinical investigation of parents of patients with seemingly sporadic mutations is essential to determine their residual chance of gonadal and/or somatic mosaicism, unless a mosaic pattern is detected in the index patient, proving a de novo event. In our data set, the exclusion of signs of TSC in the parents of a patient with TSC reduced the chance of one of the parents to be a (mosaic) mutation carrier from 10% to 2%. In the five families with somatic mosaicism, the parent was given the diagnosis after the diagnosis was made in the child.

Base Sequence↗