Description of a dinucleotide repeat polymorphism in the human elastin gene and its use to confirm assignment of the gene to chromosome 7

Simple, rapid and inexpensive quantitative fluorescent PCR method for detection of microdeletion and microduplication syndromes

Because of economic limitations, the cost-effective diagnosis of patients affected with rare microdeletion or microduplication syndromes is a challenge in developing countries. Here we report a sensitive, rapid, and affordable detection method that we have called Microdeletion/Microduplication Quantitative Fluorescent PCR (MQF-PCR). Our procedure is based on the finding of genomic regions with high homology to segments of the critical microdeletion/microduplication region. PCR amplification of both using the same primer pair, establishes competitive kinetics and relative quantification of amplicons, as happens in microsatellite-based Quantitative Fluorescence PCR. We used patients with two common microdeletion syndromes, the Williams-Beuren syndrome (7q11.23 microdeletion) and the 22q11.2 microdeletion syndromes and discovered that MQF-PCR could detect both with 100% sensitivity and 100% specificity. Additionally, we demonstrated that the same principle could be reliably used for detection of microduplication syndromes, by using patients with the Lubs (MECP2 duplication) syndrome and the 17q11.2 microduplication involving the NF1 gene. We propose that MQF-PCR is a useful procedure for laboratory confirmation of the clinical diagnosis of microdeletion/microduplication syndromes, ideally suited for use in developing countries, but having general applicability as well.

William's syndrome: gene expression is related to parental origin and regional coordinate control

William's syndrome (WS) features a spectrum of neurocognitive and behavioral abnormalities due to a rare 1.5 MB deletion that includes about 24-28 genes on chromosome band 7q11.23. Study of the expression of these genes from the single normal copy provides an opportunity to elucidate the genetic and epigenetic controls on these genes as well as their roles in both WS and normal brain development and function. We used quantitative RT-PCR to determine the transcriptional level of 14 WS gene markers in a cohort of 77 persons with WS and 48 normal controls. Results reported here: (1) show that the expression of the genes deleted in WS is decreased in some but not all cases, (2) demonstrate that the parental origin of the deletion contributes to the level of expression of GTF2I independently of age and gender and (3) indicate that the correlation of expression between GTF2I and some other genes in the WS region differs in WS subjects and normal controls, which in turn points toward a regulatory role for this gene. Interspecies comparisons suggest GTF2I may play a key role in normal brain development.

Echocardiographic findings in patients with Williams-Beuren syndrome

BACKGROUND

Williams-Beuren syndrome is a multisystem developmental disorder caused by a microdeletion at chromosome 7q11.23. In its classic form it includes dysmorphic facial features, joint contractures, retardation of growth and mental development, gregarious personality, visuospatial cognitive deficits, hypercalcemia, primary or secondary hypertension and cardiovascular disorders.

AIM

Clinical diagnosis of Williams-Beuren syndrome can be a challenge in young patients if none of the characteristic cardiovascular features, i.e. supravalvular aortic stenosis or pulmonary artery stenosis, are present. Our aim was to demonstrate the changes in cardiovascular lesions during the postnatal development of Williams-Beuren patients and to follow all cardiovascular findings beyond the most common ones.

METHODS

The cardiovascular status of 29 patients with Williams-Beuren syndrome (mean age 12.8 years) was recorded in correlation with age.

RESULTS

Cardiovascular diagnoses changed in the majority (72.4%) of patients. Interestingly, 44.8% of the patients had periods with no reported cardiovascular disease. Furthermore, 65.5% of the patients experienced periods when none of the typical cardiovascular lesions, i.e. diffuse or localized supravalvular aortic stenosis and/or pulmonary artery stenosis, were detected. Spontaneous regression and progression of both supravalvular aortic stenosis and pulmonary artery stenosis were observed. An unexpectedly high frequency (41%) of mitral valve disorders was found.

CONCLUSIONS

Our study showed that temporary absence of and changes in cardiovascular findings are frequent in Williams-Beuren syndrome. These results could contribute to the refinement of diagnostic criteria and recommendations for cardiovascular follow-up of patients with this syndrome.

Discriminating power of localized three-dimensional facial morphology

Many genetic syndromes involve a facial gestalt that suggests a preliminary diagnosis to an experienced clinical geneticist even before a clinical examination and genotyping are undertaken. Previously, using visualization and pattern recognition, we showed that dense surface models (DSMs) of full face shape characterize facial dysmorphology in Noonan and in 22q11 deletion syndromes. In this much larger study of 696 individuals, we extend the use of DSMs of the full face to establish accurate discrimination between controls and individuals with Williams, Smith-Magenis, 22q11 deletion, or Noonan syndromes and between individuals with different syndromes in these groups. However, the full power of the DSM approach is demonstrated by the comparable discriminating abilities of localized facial features, such as periorbital, perinasal, and perioral patches, and the correlation of DSM-based predictions and molecular findings. This study demonstrates the potential of face shape models to assist clinical training through visualization, to support clinical diagnosis of affected individuals through pattern recognition, and to enable the objective comparison of individuals sharing other phenotypic or genotypic properties.

The association of Buschke-Ollendorf syndrome and nail-patella syndrome

Buschke-Ollendorf syndrome and nail-patella syndrome are both rare connective tissue disorders inherited in an autosomal dominant pattern and characterized by cutaneous and bone lesions. We describe a 3-year-old boy and his family who showed clinical features of both Buschke-Ollendorf syndrome and nail-patella syndrome. To our knowledge, this association has not been reported previously, suggesting that these two connective tissue disorders may share the same gene location with different mutations or involve different mutated genes that share downstream segments of their signaling pathways. Furthermore, this young patient is also affected by a chronic idiopathic neutropenia usually not observed in Buschke-Ollendorf syndrome or nail-patella syndrome.

Genomewide-linkage and haplotype-association studies map intracranial aneurysm to chromosome 7q11

Rupture of intracranial aneurysms (IAs) causes subarachnoid hemorrhage, a devastating condition with high morbidity and mortality. Angiographic and autopsy studies show that IA is a common disorder, with a prevalence of 3%-6%. Although IA has a substantial genetic component, little attention has been given to the genetic determinants. We report here a genomewide linkage study of IA in 104 Japanese affected sib pairs in which positive evidence of linkage on chromosomes 5q22-31 (maximum LOD score [MLS] 2.24), 7q11 (MLS 3.22), and 14q22 (MLS 2.31) were found. The best evidence of linkage is detected at D7S2472, in the vicinity of the elastin gene (ELN), a candidate gene for IA. Fourteen distinct single-nucleotide polymorphisms (SNPs) were identified in ELN, and no obvious allelic association between IA and each SNP was observed. The haplotype between the intron-20/intron-23 polymorphism of ELN is strongly associated with IA (P=3.81x10-6), and homozygous patients are at high risk (P=.002), with an odds ratio of 4.39. These findings suggest that a genetic locus for IA lies within or close to the ELN locus on chromosome 7.

Severe tortuosity and stenosis of the systemic, pulmonary and coronary vessels in 12 patients with similar phenotypic features: a new syndrome?

We describe what is, to the best of our knowledge, a previously unreported association in patients with similar facial features, skin and joint laxity, of lengthening and tortuosity of systemic, pulmonary and coronary vessels. We evaluated 12 patients with similar phenotypes, from eight different families. Detailed echocardiographic and angiographic evaluations were performed in all, and biopsies of the skin in seven. All patients have elongated facies, prominent ears, micrognathia and laxity of their joints. Angiographic pictures showed a varying degree of lengthening and tortuosity of systemic, pulmonary, and coronary arteries. Pulsatile carotid arteries formed cervical masses in 2 patients, and three had severe renal arterial stenoses. All showed varying degrees of branch and peripheral pulmonary arterial stenosis, necessitating placement of stents in six. Biopsy of the skin proved normal in all seven patients studied, thus excluding cutis laxa, Ehlers-Danlos and Marfan syndromes. The constellation of abnormalities suggests a genetic syndrome of connective tissue etiology. Further genetic studies, and gene mapping, are underway.

Elastin region deletions in Williams syndrome

Williams syndrome (WS) is considered a contiguous gene syndrome, with most patients having a 1.5-Mb deletion of chromosome 7q11.23 containing the elastin gene and flanking genes. Studies of the frequency, extent, and origin of these deletions are ongoing in many labs to discover ultimately the molecular and pathogenetic basis for WS. An analysis of 9 sporadic WS families with typical phenotypes was performed by genotyping polymorphisms in the region. This study revealed deletions in all 9 patients, with one showing a novel deletion extending much further centromeric than any other WS deletions yet reported.

Elastin gene deletions in Williams syndrome patients result in altered deposition of elastic fibers in skin and a subclinical dermal phenotype

Williams syndrome (WS) is a complex developmental disorder with multisystem involvement known to be the result of a microdeletion in the q11.23 region of chromosome 7. This deletion involves several genes, including the elastin gene. Although elastic fibers are important constituents of skin, little is known about the skin phenotype in WS patients. We have therefore studied the skin of four WS patients in which we've shown the deletion of one copy of the elastin gene. Physical examination and indirect immunofluorescent microscopy of elastin did not detect any major phenotypic or morphologic changes in the skin. We were able, however, to show subtle textural changes in skin and, by electron microscopy, that the amorphous component of elastic fibers in WS patients was consistently reduced when compared to normal controls. These findings indicate that deletion of one copy of the elastin gene results in reduced deposition of elastin in dermal elastic fibers, an altered elastic fiber ultrastructure, and a subclinical dermal phenotype in the children and young adult patients analyzed in this study.

Williams syndrome: use of chromosomal microdeletions as a tool to dissect cognitive and physical phenotypes

In Williams syndrome (WS), a deletion of approximately 1.5 Mb on one copy of chromosome 7 causes specific physical, cognitive, and behavioral abnormalities. Molecular dissection of the phenotype may be a route to identification of genes important in human cognition and behavior. Among the genes known to be deleted in WS are ELN (which encodes elastin), LIMK1 (which encodes a protein tyrosine kinase expressed in the developing brain), STX1A (which encodes a component of the synaptic apparatus), and FZD3. Study of patients with deletions or mutations confined to ELN showed that hemizygosity for elastin is responsible for the cardiological features of WS. LIMK1 and STX1A are good candidates for cognitive or behavioral aspects of WS. Here we describe genetic and psychometric testing of patients who have small deletions within the WS critical region. Our results suggest that neither LIMK1 hemizygosity (contrary to a previous report) nor STX1A hemizygosity is likely to contribute to any part of the WS phenotype, and they emphasize the importance of such patients for dissecting subtle but highly penetrant phenotypes.

Genetic analysis of structural elastic fiber and collagen genes in familial adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis is a genetic disorder of unknown etiology. Scoliosis is a clinical feature of inherited connective-tissue disorders including Marfan syndrome. Mutations within the gene of FBN1 (fibrillin 15), a component of the extracellular matrix, are now linked to Marfan syndrome and similar clinical phenotypes. This study investigated the potential association of structural genes encoding for extracellular matrix components of FBN1, elastin, and one of the polypeptides of type-I collagen (COL1A2) with familial adolescent idiopathic scoliosis. Eleven pedigrees, including 96 individuals, were identified in which adolescent idiopathic scoliosis segregated in an apparent autosomal dominant pattern. Fifty-two individuals were determined to be affected with scoliosis. Genomic DNA was analyzed by genetic linkage utilizing four intragenic markers for the structural genes of FBN1, elastin, and COL1A2. Collectively, our results exclude the structural genes of FBN1, elastin, and COL1A2 as candidate genes within these families. However, when viewed individually, specific markers cannot be excluded within all of the families. This information complements previously reported data that fibrillin production and matrix incorporation from scoliotic fibroblasts in vitro are normal in more than 80% of patients studied.

LIM-kinase1 hemizygosity implicated in impaired visuospatial constructive cognition

To identify genes important for human cognitive development, we studied Williams syndrome (WS), a developmental disorder that includes poor visuospatial constructive cognition. Here we describe two families with a partial WS phenotype; affected members have the specific WS cognitive profile and vascular disease, but lack other WS features. Submicroscopic chromosome 7q11.23 deletions cosegregate with this phenotype in both families. DNA sequence analyses of the region affected by the smallest deletion (83.6 kb) revealed two genes, elastin (ELN) and LIM-kinase1 (LIMK1). The latter encodes a novel protein kinase with LIM domains and is strongly expressed in the brain. Because ELN mutations cause vascular disease but not cognitive abnormalities, these data implicate LIMK1 hemizygosity in imparied visuospatial constructive cognition.

Identification of a case of maternal uniparental disomy of chromosome 10 associated with confined placental mosaicism

We report a case of maternal uniparental disomy of chromosome 10 discovered after chorionic villus sampling (CVS). Direct preparations revealed mosaic trisomy 10, while cultured CVS cells, as well as amniotic fluid cells, showed only a normal 46,XY complement. DNA analysis using microsatellite markers showed both chromosomes 10 to have been inherited from the mother. The pregnancy was complicated by polyhydramnios. A phenotypically normal male infant of appropriate size was delivered by Caesarean section at 41 weeks' gestation. Since only the direct preparations showed trisomy 10, this case illustrates the importance of CVS direct preparations in the detection of pregnancies at risk of uniparental disomy (UPD). Although the increased frequency of confined placental mosaicism (CPM) diagnosed when direct preparations are performed has been viewed negatively, identification of both CPM and UPD may have biological and clinical significance for a pregnancy. Even though only a single case of maternal disomy 10 is reported here, the apparently normal phenotype provides evidence that there are no major imprinted loci on chromosome 10 that affect in utero growth and development. However, other potential effects such as mental retardation will require long-term follow-up of this as well as additional cases.