M. Litt

Detection and characterization of additional DNA polymorphisms in the dopamine D2 receptor gene

The gene encoding the dopamine D2 receptor (DRD2) has been suggested as a candidate gene for several mental disorders. We previously described the cloning and chromosomal mapping (to 11q22-q23) of a human DRD2 gene as well as its use for the detection of a two-allele TaqI RFLP with a minor allele frequency of 0.24, corresponding to a PIC of 0.30. Family linkage utilizing DRD2 would be facilitated if the PIC of the DRD2 locus were increased. To this end, we have used additional phage and cosmid clones in the vicinity of DRD2 to identify a new two-allele TaqI RFLP as well as a TG microsatellite polymorphism with a PIC of 0.62. We report localizations of the three polymorphisms on the restriction map of the DRD2 locus. The TaqI RFLPs are in apparent linkage equilibrium with the microsatellite, yielding a highly informative compound marker locus with a PIC of 0.76.

Lamin A/C mutation analysis in a cohort of 324 unrelated patients with idiopathic or familial dilated cardiomyopathy

BACKGROUND Lamin A/C mutations are a well-established cause of dilated cardiomyopathy (DCM), although their frequency has not been examined in a large cohort of patients. We sought to examine the frequency of mutations in LMNA, the gene encoding lamin A/C, in patients with idiopathic (IDC) or familial dilated cardiomyopathy (FDC). METHODS Clinical cardiovascular data, family histories, and blood samples were collected from 324 unrelated IDC probands, of whom 187 had FDC. DNA samples were sequenced for nucleotide alterations in LMNA. Likely protein-altering mutations were followed up by evaluating additional family members, when possible. RESULTS We identified 18 protein-altering LMNA variants in 19 probands or 5.9% of all cases (7.5% of FDC; 3.6% of IDC). Of the 18 alterations, 11 were missense (one present in 2 kindreds), 3 were nonsense, 3 were insertion/deletions, and 1 was a splice site alteration. Conduction system disease and DCM were common in carriers of LMNA variants. Unexpectedly, in 6 of the 19 kindreds with a protein-altering LMNA variant (32%), at least one affected family member was negative for the LMNA variant. CONCLUSIONS Lamin A/C variants were observed with a frequency of 5.9% in probands with DCM. The novel observation of FDC pedigrees in which not all affected individuals carry the putative disease-causing LMNA mutation suggests that some protein-altering LMNA variants are not causative or that some proportion of FDC may be because of multiple causative factors. These findings warrant increased caution in FDC research and molecular diagnostics.

Coding sequence mutations identified in MYH7, TNNT2, SCN5A, CSRP3, LBD3, and TCAP from 313 patients with familial or idiopathic dilated cardiomyopathy.

Background: More than 20 genes have been reported to cause idiopathic and familial dilated cardiomyopathy (IDC/FDC), but the frequency of genetic causation remains poorly understood.

Autosomal-dominant congenital cataract associated with a deletion mutation in the human beaded filament protein gene BFSP2

Congenital cataracts are a common major abnormality of the eye that frequently cause blindness in infants. At least one-third of all cases are familial; autosomal-dominant congenital cataract appears to be the most-common familial form in the Western world. Elsewhere, in family ADCC-3, we mapped an autosomal-dominant cataract gene to chromosome 3q21-q22, near the gene that encodes a lens-specific beaded filament protein gene, BFSP2. By sequencing the coding regions of BFSP2, we found that a deletion mutation, DeltaE233, is associated with cataracts in this family. This is the first report of an inherited cataract that is caused by a mutation in a cytoskeletal protein.

The CEPH Consortium Linkage Map of Human Chromosome 11

The CEPH consortium framework map of chromosome 11 is presented. The map was generated from CEPH family DNAs with 181 probe/enzyme combinations contributed by 20 laboratories. Seventy-seven of the loci are defined by microsatellite polymorphisms that can be typed by the PCR. A total of 42 loci have been placed on the map with likelihood support of at least 1000:1. The female, male, and sex-average maps extend for 179.6, 110.8, and 145.3 cM, respectively. The largest interval on the sex-average map is less than 11 cM, and the average distance between uniquely placed loci is 4 cM. The genotypic data obtained for map construction have been used to identify the positions of crossovers on the chromosomes of CEPH family children, allowing the localization of new markers without computationally intensive likelihood models and providing a basis for efficient extension of the linkage map to higher resolution.

Paroxysmal kinesigenic dyskinesia and infantile convulsions: Clinical and linkage studies

Objective: To clinically characterize affected individuals in families with paroxysmal kinesigenic dyskinesia (PKD), examine the association with infantile convulsions, and confirm linkage to a pericentromeric chromosome 16 locus. Background: PKD is characterized by frequent, recurrent attacks of involuntary movement or posturing in response to sudden movement, stress, or excitement. Recently, an autosomal dominant PKD locus on chromosome 16 was identified. Methods: The authors studied 11 previously unreported families of diverse ethnic background with PKD with or without infantile convulsions and performed linkage analysis with markers spanning the chromosome 16 locus. Detailed clinical questionnaires and interviews were conducted with affected and unaffected family members. Results: Clinical characterization and sampling of 95 individuals in 11 families revealed 44 individuals with paroxysmal dyskinesia, infantile convulsions, or both. Infantile convulsions were surprisingly common, occurring in 9 of 11 families. In only two individuals did generalized seizures occur in later childhood or adulthood. The authors defined a 26-cM region using linkage data in 11 families (maximum lod score 6.63 at θ = 0). Affected individuals in one family showed no evidence for a shared haplotype in this region, implying locus heterogeneity. Conclusions: Identification and characterization of the PKD/infantile convulsions gene will provide new insight into the pathophysiology of this disorder, which spans the phenotypic spectrum between epilepsy and movement disorder.

A hypervariable repeated sequence on human chromosome 1p36

SummaryWhen used to probe Southern blots of TaqI-digested DNAs from unrelated individuals, p1–79, a 900 bp subclone of a random human cosmid, revealed at least 50 fragments, many of which were polymorphic. Each of 27 unrelated individuals tested with p1–79 displayed a distinct band pattern. Similar variation was seen with several other enzymes, including HaeIII, MspI, PstI and PvuII, whereas other enzymes yielded primarily large fragments of greater than 40 kb. In situ hybridization of p1–79 showed that the loci of hybridization are clustered on human chromosome band 1p36; localization of all TaqI fragments to chromosome 1 was confirmed with a human-rodent somatic cell hybrid panel. DNA sequencing of p1–79 revealed several copies of a 39 bp repeat whose variation in copy number might be the basis of the observed length polymorphisms. Studies of 3-generation Utah families suggest that the numerous restriction fragments homologous to p1–79 are inherited as haplotypes, implying that recombination within this cluster of loci is rare and allowing the cluster to serve as a useful marker for human gene mapping.

Mutations of Presenilin Genes in Dilated Cardiomyopathy and Heart Failure

Two common disorders of the elderly are heart failure and Alzheimer disease (AD). Heart failure usually results from dilated cardiomyopathy (DCM). DCM of unknown cause in families has recently been shown to result from genetic disease, highlighting newly discovered disease mechanisms. AD is the most frequent neurodegenerative disease of older Americans. Familial AD is caused most commonly by presenilin 1 (PSEN1) or presenilin 2 (PSEN2) mutations, a discovery that has greatly advanced the field. The presenilins are also expressed in the heart and are critical to cardiac development. We hypothesized that mutations in presenilins may also be associated with DCM and that their discovery could provide new insight into the pathogenesis of DCM and heart failure. A total of 315 index patients with DCM were evaluated for sequence variation in PSEN1 and PSEN2. Families positive for mutations underwent additional clinical, genetic, and functional studies. A novel PSEN1 missense mutation (Asp333Gly) was identified in one family, and a single PSEN2 missense mutation (Ser130Leu) was found in two other families. Both mutations segregated with DCM and heart failure. The PSEN1 mutation was associated with complete penetrance and progressive disease that resulted in the necessity of cardiac transplantation or in death. The PSEN2 mutation showed partial penetrance, milder disease, and a more favorable prognosis. Calcium signaling was altered in cultured skin fibroblasts from PSEN1 and PSEN2 mutation carriers. These data indicate that PSEN1 and PSEN2 mutations are associated with DCM and heart failure and implicate novel mechanisms of myocardial disease.

A detailed genetic map of the long arm of chromosome 11

We describe 14 new restriction fragment length polymorphisms, corresponding to 13 loci on the long arm of chromosome 11. A detailed genetic map of chromosome 11q has been constructed from these and other loci (a total of 31 loci) typed in 59 reference families. The 23 most informative markers were selected to establish a map with a strongly supported order; regional localizations are provided for eight other markers. The loci span 88 cM in males and 148 cM in females and form a dense continuum on 11q. These ordered polymorphic markers will be of help in studying the genes responsible for several diseases that have been localized to this region, including genes responsible for multiple endocrine neoplasia type I (MEN1), ataxia telangiectasia (AT), tuberous sclerosis (TSC), and some forms of asthma and rhinitis.

Analysis of the α-synuclein G209A mutation in familial Parkinson's disease

THE LANCET • Vol 351 • January 3, 1998 37 described by Celermajer and colleagues. We collected blood at 0, 2, and 4 h during the study to measure total plasma homocysteine by high-performance liquid chromatography. Mean flow-mediated dilatation fell after methionine (4·6 [SE 0·8]%, at baseline to 0·7 [1·4]% and –1·3 [0·8]%, at 2 h and 4 h, respectively) but not after placebo (5·2 [1·4]% at baseline, 6·6 [1·5]% and 4·8 [1·3]%, at 2 h and 4 h, respectively; p<0·001). By contrast, there was no significant difference in glyceryltrinitrate-induced brachial-artery dilatation after methionine (22·4 [1·7]%, 19·8 [1·6]% at baseline and 4 h, respectively) or placebo (20·9 [1·6]% and 20·8 [1·8]% at baseline and 4 h, respectively). There was a linear increase in mean plasma homocysteine concentration after oral methionine (from 9·3 [1·0]% at baseline to 24·1 [3·6] and 30·5 [3·0] mol/L at 2 and 4 h, respectively; p<0·0001). Flow-mediated dilatation was strongly related to plasma homocysteine (p<0·001, figure), with no independent effect of time. Our main findings are that an acute increase in plasma homocysteine is associated with substantial impairment of endothelial function in healthy human volunteers and that this relation is inverse and linear. Brachial artery flow-mediated dilatation is endothelium dependent and largely mediated by nitric oxide. Our findings, therefore, suggest impaired endothelial nitric-oxide activity in healthy individuals during acute hyperhomocysteinaemia. Endothelial dysfunction occurred at concentrations of homocysteine that were only two-fold higher than the fasting state, and similar to those associated with an increased risk of acute myocardial infarction, stroke, and venous thrombosis. These findings may help to explain the incremental risk of vascular events with increasing homocysteine concentrations, and accord with previous reports of dose-dependent and time-dependent effects of homocysteine on endothelial cellular function. Invitro studies show that exposure of endothelial cells to homocysteine results in oxidative effects, including generation of superoxide anion radicals and hydrogen peroxide, which lead to inactivation of nitric oxide and endothelial-cell damage. The resultant endothelial dysfunction may then contribute to vasospasm, thrombosis, and progression of atherosclerosis.