D. J. J. Halley

Common C-to-T Substitution at Position −480 of the Hepatic Lipase Promoter Associated With a Lowered Lipase Activity in Coronary Artery Disease Patients

We studied the molecular basis of low hepatic lipase (HL) activity in normolipidemic male patients with angiographically documented coronary artery disease (CAD). In 18 subjects with a lowered HL activity (< 225 mU/mL), all nine exons of the HL gene and part of the promoter region (nucleotides -524 to +7) were sequenced. No structural mutations in the coding part of the HL gene were found, but 50% of the subjects showed a C-to-T substitution at nucleotide -480. Screening for the base substitution in 782 patients yielded an allele frequency of 0.213 (297 heterozygotes, 18 homozygotes). In a group of 316 nonsymptomatic control subjects, the allele frequency was 0.189, which is significantly less than in the CAD patients (P = .035). In the CAD patients, the C-to-T substitution was associated with a lowered lipase activity (heterozygotes -15%, homozygotes -20%). The patients were divided into quartiles on the basis of HL activity. Sixty percent (allele frequency 0.32) of the patients in the lowest quartile (HL activity < 306 mU/mL) had the gene variant against 27% (allele frequency 0.14) in the highest quartile (HL activity > 466 mU/mL). In the noncarriers, but not in the carriers, HL activity was related with plasma insulin, being increased at higher insulin concentration. Homozygous carriers had a significantly higher HDL cholesterol level-than noncarriers (1.13 +/- 0.28 mmol/L versus 0.92 +/- 0.22 mmol/L, P < .02). Our results show that a C-to-T substitution at -480 of the HL promoter is associated with a lowered HL activity. The base substitution, or a closely linked gene variation, may contribute to the variation in HL activity and affect plasma lipoprotein metabolism.

Sporadic Imprinting Defects in Prader-Willi Syndrome and Angelman Syndrome: Implications for Imprint-Switch Models, Genetic Counseling, and Prenatal Diagnosis

The Prader-Willi syndrome (PWS) and the Angelman syndrome (AS) are caused by the loss of function of imprinted genes in proximal 15q. In approximately 2%-4% of patients, this loss of function is due to an imprinting defect. In some cases, the imprinting defect is the result of a parental imprint-switch failure caused by a microdeletion of the imprinting center (IC). Here we describe the molecular analysis of 13 PWS patients and 17 AS patients who have an imprinting defect but no IC deletion. Heteroduplex and partial sequence analysis did not reveal any point mutations of the known IC elements, either. Interestingly, all of these patients represent sporadic cases, and some share the paternal (PWS) or the maternal (AS) 15q11-q13 haplotype with an unaffected sib. In each of five PWS patients informative for the grandparental origin of the incorrectly imprinted chromosome region and four cases described elsewhere, the maternally imprinted paternal chromosome region was inherited from the paternal grandmother. This suggests that the grandmaternal imprint was not erased in the fathers germ line. In seven informative AS patients reported here and in three previously reported patients, the paternally imprinted maternal chromosome region was inherited from either the maternal grandfather or the maternal grandmother. The latter finding is not compatible with an imprint-switch failure, but it suggests that a paternal imprint developed either in the maternal germ line or postzygotically. We conclude (1) that the incorrect imprint in non-IC-deletion cases is the result of a spontaneous prezygotic or postzygotic error, (2) that these cases have a low recurrence risk, and (3) that the paternal imprint may be the default imprint.

Cognitive impairment in tuberous sclerosis complex is a multifactorial condition

Objective: In patients with tuberous sclerosis complex (TSC), associations between tuber number, infantile spasms, and cognitive impairment have been proposed. We hypothesized that the tuber/brain proportion (TBP), the proportion of the total brain volume occupied by tubers, would be a better determinant of seizures and cognitive function than the number of tubers. We investigated tuber load, seizures, and cognitive function and their relationships. Methods: Tuber number and TBP were characterized on three-dimensional fluid-attenuated inversion recovery MRI with an automated tuber segmentation program. Seizure histories and EEG recordings were obtained. Intelligence equivalents were determined and an individual cognition index (a marker of cognition that incorporated multiple cognitive domains) was calculated. Results: In our sample of 61 patients with TSC, TBP was inversely related to the age at seizure onset and to the intelligence equivalent and tended to be inversely related to the cognition index. Further, a younger age at seizure onset or a history of infantile spasms was related to lower intelligence and lower cognition index. In a multivariable analysis, only age at seizure onset and cognition index were related. Conclusions: Our systematic analysis confirms proposed relationships between tuber load, epilepsy and cognitive function in tuberous sclerosis complex (TSC), but also indicates that tuber/brain proportion is a better predictor of cognitive function than tuber number and that age at seizure onset is the only independent determinant of cognitive function. Seizure control should be the principal neurointervention in patients with TSC.

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

Abstract 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.

A prospective 10 year follow up study of patients with neurofibromatosis type 1

OBJECTIVE To establish the prevalence and incidence of symptoms and complications in children with neurofibromatosis type 1 (NF1) and to assess possible risk factors for the development of complications. DESIGN A 10 year prospective multidisciplinary follow up study. PATIENTS One hundred and fifty children diagnosed with NF1 according to criteria set by the National Institutes of Health. RESULTS In 62 of 150 children (41.3%) complications were present, including 42 (28.0%) children with one complication, 18 (12.0%) with two complications, and two (1.3%) with three complications (mean (SD) duration of follow up 4.9 (3.8) years). Ninety five of the 150 children presented without complications (follow up, 340.8 person-years). The incidence of complications was 2.4/100 person-years in this group. An association was found between behavioural problems and the presence of complications. CONCLUSION This is the largest single centre case series of NF1 affected children followed until 18 years of age. Children with NF1, including those initially presenting without complications, should have regular clinical examinations.

Overlapping neurologic and cognitive phenotypes in patients with TSC1 or TSC2 mutations

Objective: The purpose of this study was to systematically analyze the associations between different TSC1 and TSC2 mutations and the neurologic and cognitive phenotype in patients with tuberous sclerosis complex (TSC). Methods: Mutation analysis was performed in 58 patients with TSC. Epilepsy variables, including EEG, were classified. A cognition index was determined based on a comprehensive neuropsychological assessment. On three-dimensional fluid-attenuated inversion recovery MR images, an automated tuber segmentation program detected and calculated the number of tubers and the proportion of total brain volume occupied by tubers (tuber/brain proportion [TBP]). Results: As a group, patients with a TSC2 mutation had earlier age at seizure onset, lower cognition index, more tubers, and a greater TBP than those with a TSC1 mutation, but the ranges overlapped considerably. Familial cases were older at seizure onset and had a higher cognition index than nonfamilial cases. Patients with a mutation deleting or directly inactivating the tuberin GTPase activating protein (GAP) domain had more tubers and a greater TBP than those with an intact GAP domain. Patients with a truncating TSC1 or TSC2 mutation differed from those with nontruncating mutations in seizure types only. Conclusions: Although patients with a TSC1 mutation are more likely to have a less severe neurologic and cognitive phenotype than those with a TSC2 mutation, the considerable overlap between both aspects of the phenotype implies that prediction of the neurologic and cognitive phenotypes in individuals with tuberous sclerosis complex should not be based on their particular TSC1 or TSC2 mutation.

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.

Screening for the fragile X syndrome among the mentally retarded: a clinical study

The fragile X syndrome is characterised by mental retardation with other features such as a long face with large, protruding ears, macro-orchidism, and eye gaze avoidance. This X linked disorder is caused by an expanded CGG repeat in the first exon of the fragile X mental retardation (FMR1) gene which is associated with shut down of transcription and absence of the fragile X mental retardation protein (FMRP). Molecular testing is used for detection of patients and carriers of the fragile X syndrome. In a screening programme for the fragile X syndrome in the south west of The Netherlands, 896 males and 685 females with an unknown cause for their mental retardation were scored on seven fragile X features. All were tested by DNA analysis and 11 new cases were diagnosed. The seven item checklist allowed exclusion from further testing in 86% of the retarded males (95% CI 0.83-0.88) without missing either any of the newly diagnosed cases or, in retrospect, any of the 50 previously diagnosed cases known to our department. These results showed that clinical preselection for DNA testing in mentally retarded males is feasible using a simple scoring list, which will increase the efficiency of further testing eightfold.

New Polymorphic DNA Marker Close to the Fragile Site FRAXA

DNA from a human-hamster hybrid cell line, 908-K1B17, containing a small terminal portion of the long arm of the human X chromosome as well as the pericentric region of 19q was used as starting material for the isolation of an X-chromosome-specific DNA segment, RN1 (DXS369), which identifies a XmnI RFLP. Linkage analysis in fragile X families resulted in a maximum lod score of 15.3 at a recombination fraction of 0.05 between RN1 and fra(X). Analysis of recombinations around the fra(X) and distal to DXS105. Analysis of the marker content of hybrid cell line 908K1B17 suggests the localization of RN1 between DXS98 and fra(X). Heterozygosity of DXS369 is approximately 50%, which extends the diagnostic potential of RFLP analysis in fragile X families significantly.

Frequency of Von Hippel-Lindau germline mutations in classic and non-classic Von Hippel-Lindau disease identified by DNA sequencing, Southern blot analysis and multiplex ligation-dependent probe amplification

The current clinical diagnosis of Von Hippel‐Lindau (VHL) disease demands at least one specific a sporadic VHL manifestation in a patient with familial VHL disease, or, in asporadic patient, at least two or more hemangioblastomas or a single hemangioblastoma in combination with a typical visceral lesion. To evaluate this definition, we studied the frequency of germline VHL mutation in three patients groups: (i) multi‐organ involvement (classic VHL), (ii) limited VHL manifestations meeting criteria (non‐classic VHL) and (iii) patients with VHL‐associated tumors not meeting current diagnostic VHL criteria. In addition, we validated multiplex ligation‐dependent probe amplification (MLPA) as a rapid and reliable quantitative method for the identification of germline VHL deletions. The frequency of germline VHL mutations was very high in classic VHL cases with multi‐organ involvement (95%), lower in non‐classic cases that meet current diagnostic criteria but have limited VHL manifestations or single‐organ involvement (24%) and low (3.3%), but tangible in cases not meeting current diagnostic VHL criteria. The detection of germline VHL mutations in patients or families with limited VHL manifestations, or single‐organ involvement is relevant for follow‐up of probands and early identification of at‐risk relatives.