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W T Brown

Publications and source records attributed to W T Brown.

At least 91 records · Page 5Linked to original sources
PubMed1994

New X-linked mental retardation (XLMR) syndrome with distinct facial appearance and growth retardation.

We report on 2 brothers and their nephew with an apparently new X-linked mental retardation (XLMR) syndrome characterized by a distinct facial appearance, growth retardation, and severe mental retardation. The facial traits included triangular shape; bifrontal narrowness; malar flatness; blepharophimosis; very deeply set eyes; epicanthus inversus; bulbous nose; low hairline; low-set, deeply cupped, and protruding ears; short ill-defined philtrum; and thin tented upper lip. These facial anomalies are particularly striking and recognizable even at birth. The boys were small for gestational age and remained below -2 SD in growth parameters. With age, large joint contractures developed. Pectus excavatum was apparent at birth but became more obvious with age. Global developmental delay was evident in infancy. The brothers were nonverbal while their nephew spoke simple words. Optic atrophy, esotropia, nystagmus, and spastic diplegia were evident. They were self-abusive, hyperactive, and poorly coordinated. CT scans demonstrated atrophic hydrocephalus. No EEG abnormalities were detected. Karyotypes were 46,XY and fragile X negative. Routine chemistries; amino, organic, and uronic acids; oligosaccharides; lysosomal enzymes; and very long chain fatty acids were normal. Remarkable phenotypic similarity between these brothers and their nephew and lack of manifestations in their mothers makes X-linked recessive inheritance likely. This syndrome, which does not appear to have been reported previously, adds to the delineation of XLMR.

Abnormalities, Multiple↗
PubMed1994

Postnatal confirmation of prenatally diagnosed trisomy 16 mosaicism in two phenotypically abnormal liveborns.

Two phenotypically abnormal liveborns in whom trisomy 16 mosaicism was diagnosed prenatally by amniocentesis are described. Analysis of a percutaneous umbilical blood sample in one case revealed a normal chromosomal complement. Ultrasound examinations performed at the time of amniocentesis were normal. Serial sonography during the late second and third trimesters demonstrated progressive intrauterine growth retardation (IUGR) in both fetuses and a cardiac defect in one. At birth, both infants had dysmorphic features and multiple congenital anomalies. Trisomy 16 mosaicism was confirmed postnatally in both infants in skin fibroblasts; however, peripheral blood samples contained only chromosomally normal cells. The two mosaic trisomy 16 cases described in this report, together with the five confirmed cases reported previously, demonstrate the need for caution in the counselling of patients when trisomy 16 mosaicism is diagnosed prenatally in amniotic fluid samples. Such cases potentially can result in the birth of dysmorphic infants with significant birth defects, growth retardation, and possible developmental disabilities.

Abnormalities, Multiple↗
PubMed1993

Rapid fragile X carrier screening and prenatal diagnosis using a nonradioactive PCR test.

OBJECTIVE: To develop a rapid, nonradioactive test using the polymerase chain reaction (PCR) capable of detecting full fragile X mutations, premutations, and resolving normal alleles and to apply this to prenatal diagnosis and carrier screening of pregnant women at risk for fragile X carrier status. DESIGN: Prenatal and blood sample PCR analysis with confirmation by direct Southern blotting and cytogenetic techniques. SETTING: Samples sent to a DNA diagnostic research laboratory at a tertiary referral center. PARTICIPANTS: Pregnant women with a family history of undiagnosed mental retardation or known fragile X syndrome and controls. RESULTS: A rapid, nonradioactive PCR screening protocol for the fragile X mental retardation-1 gene for both normal and mutant alleles was developed. Analysis of 570 control X chromosomes showed a modal number of 30 CGG repeats (range, 12 to 52 repeats) and a calculated heterozygosity of approximately 80%. No excess of homozygosity was found, indicating the test was accurate for normal allele resolution. In addition, 150 unrelated pregnant women were screened. Within known fragile X families, five of 20 pregnant women were diagnosed as carriers. Two new fragile X families were diagnosed among relatives of 130 females with family histories of undiagnosed mental retardation, although no carriers were identified. Prenatal PCR testing of 28 carriers accurately detected nine fetuses with full mutations. CONCLUSIONS: This rapid, nonradioactive PCR protocol allows accurate resolution of normal alleles as well as simultaneous detection of carrier alleles and full mutations. With this approach, efficient screening of pregnant women at risk for fragile X carrier status, subsequent genetic counseling of identified carriers, and reliable prenatal diagnosis can be offered.

Base Sequence↗
PubMed1993

Apolipoprotein E epsilon 4 allele distributions in late-onset Alzheimer's disease and in other amyloid-forming diseases.

The frequency of the allele for apolipoprotein E type 4 (epsilon 4) is increased in late-onset familial and sporadic Alzheimer's disease (AD). We have examined epsilon 4 frequencies in four distinct, normal, elderly control groups and, most importantly, in patients with amyloid-forming diseases whose epsilon 4 distributions were not previously known (Creutzfeldt-Jakob disease, familial amyloidotic polyneuropathy, Down's syndrome). There were no differences between any of these controls and published control series, cementing the relevance of epsilon 4 for late-onset AD. The increase in late-onset AD was confirmed in two new series.

Age Factors↗
PubMed1993

A complex mutable polymorphism located within the fragile X gene.

While studying founder chromosomes in the fragile X syndrome, we have unexpectedly found linkage equilibrium to FRAXAC2, an Alu-associated microsatellite within the defective gene, FMR-1. DNA sequencing of 265 chromosomes revealed 39 alleles and a complex microsatellite of form (GT)x-C-(TA)y-(T)z. A mutation rate of 3.3% was observed but only among fragile X maternally derived meioses. Finding a second mutable locus within FMR-1 suggests that the target for tandem repeat instability may not be confined to the (CGG)n repeat alone and raises the possibility of an FMR-1 mutation mechanism involving microsatellites.

Base Sequence↗
PubMed1993

Guidelines for the diagnosis of fragile X syndrome. National Fragile X Foundation.

Direct DNA analysis of the fragile X mutation has become available with the isolation of DNA probes that detect the unstable DNA sequence containing the CGG repeat. We present the various alternatives of combinations of probes and enzymes that can be used for the diagnosis of fragile X syndrome. An overview is given of all the different available probes. A different protocol is presented for postnatal and prenatal diagnosis of fragile X syndrome. This includes Southern blot analysis as well as direct analysis of the CGG repeat by PCR amplification. We discuss the role of constitutional cytogenetic analysis in the diagnosis of mentally retarded subjects and cytogenetic analysis for the diagnosis of fragile X syndrome.

Adult↗
PubMed1993

Evidence that methylation of the FMR-I locus is responsible for variable phenotypic expression of the fragile X syndrome.

DNA at the FMR-1 locus was analyzed by Southern blot using probe StB12.3 in an unusual fragile X family with six brothers, three of whom are affected with fragile X to varying degrees, two of whom are nonpenetrant carriers, and one of whom is unaffected. Fragile X chromosome studies, detailed physical examinations, and psychological testing were completed on all six. Two of the affected brothers and the two nonpenetrant brothers were found to be methylation mosaics. The three affected males spanned the phenotypic and cognitive spectrum of the fragile X syndrome. A correlation was seen between the degree of methylation and the phenotypic expression identified in the three affected males. The two males initially classified as nonpenetrant were found to have mild phenotypic expression which consisted of minor cognitive deficits and a partial physical phenotype. These two, who were negative on fragile X chromosome studies, were found on DNA analysis to have large broad smears, with approximately 97% of the DNA unmethylated. The results described here indicate that some "nonpenetrant" carrier males may have varying amounts of methylation of the FMR-1 region, which can result in mild expression of the fragile X syndrome. The apparently mild phenotypic and cognitive expression of the fragile X syndrome in the two males, initially classified as nonpenetrant, who are mosaic for hypermethylation of an expansion of the CGG repeat in the premutation range, indicates that expression of the syndrome is not confined to males with large, hypermethylated expansions (full mutation) but has instead a gradient effect with a threshold for the full expression of the phenotype.

Adult↗
PubMed1992

Detection of full fragile X mutation.

In fragile X syndrome, the most common inherited cause of mental deficiency, the underlying mutation is a large increase in the number of CGG repeats in a gene on chromosome X. We have developed a polymerase chain reaction (PCR) method to amplify across the full mutation in affected individuals. In this report, a fragile X family including a positive prenatally diagnosed fetus was analysed by PCR, and the results are consistent with direct genomic Southern blot analysis. Genetic screening of at-risk populations for fragile X can now be achieved by PCR rapidly, inexpensively, and on small samples.

Amino Acid Sequence↗
PubMed1992

Isolation and characterization of a highly polymorphic human locus (DXS455) in proximal Xq28.

Human Xq28 is highly gene dense with over 27 loci. Because most of these genes have been mapped by linkage to polymorphic loci, only one of which (DXS52) is informative in most families, a search was conducted for new, highly polymorphic Xq28 markers. From a cosmid library constructed using a somatic cell hybrid containing human Xq27.3----qter as the sole human DNA, a human-insert cosmid (c346) was identified and found to reveal variation on Southern blot analyses with female DNA digested with any of several different restriction endonucleases. Two subclones of c346, p346.8 and p346.T, that respectively identify a multiallelic VNTR locus and a frequent two-allele TaqI polymorphism were isolated. Examination of 21 unrelated females showed heterozygosity of 76 and 57%, respectively. These two markers appeared to be in linkage equilibrium, and a combined analysis revealed heterozygosity in 91% of unrelated females. Families segregating the fragile X syndrome with key Xq28 crossovers position this locus (designated DXS455) between the proximal Xq28 locus DXS296 (VK21) and the more distal locus DXS374 (1A1), which is proximal to DXS52. DXS455 is therefore the most polymorphic locus identified in Xq28 and will be useful in the genetic analysis of this gene dense region, including the diagnosis of nearby genetic disease loci by linkage.

Alleles↗
PubMed1992

Evidence of founder chromosomes in fragile X syndrome.

The mutation responsible for fragile X syndrome and myotonic dystrophy involves the amplification of a simple trinucleotide repeat sequence, which increases in successive generations of affected pedigrees accounting for increasing penetrance of both disorders. This common molecular basis suggests that the two diseases may share other genetic features, but whereas myotonic dystrophy exhibits a significant founder chromosome effect, fragile X syndrome apparently has a very high mutation frequency. By haplotype analysis of microsatellite markers which flank the fragile X unstable element, we have uncovered evidence of founder chromosomes of the fragile X 'mutation'. Disorders caused by heritable unstable elements may therefore exhibit common genetic properties including anticipation and founder chromosomes.

Base Sequence↗
PubMed1992

Progeria: a human-disease model of accelerated aging.

Progeria is a rare genetic disease with striking features that resemble accelerated aging. The inheritance pattern, paternal age effect, and lack of consanguinity argue that it is due to a sporadic dominant mutation. We have observed elevated levels of hyaluronic acid (HA) excretion in progeria patients. In several progeria patients we observed normal levels of growth hormone (GH) but very low levels of insulin-like growth factor I along with very high basal metabolic rates (BMRs). A trial of GH treatment was begun, which resulted in a marked increase in linear growth and a paradoxical drop in BMRs in these two patients. We hypothesize that the failure of patients with progeria to thrive may be due to a bioinactive form of GH and a lack of vasculogenesis caused by excess HA. An understanding of the progeria genetic mutation may define a key gene with a major effect on normal aging.

Basal Metabolism↗
PubMed1991

Analysis of neocortex in three males with the fragile X syndrome.

Fragile X [fraX] syndrome is a common hereditary disorder associated with a fragile site marker at Xq27.3 which clinically presents as a form of mental retardation (MR). Postmortem investigation of 3 fraX positive males with mild to moderate MR did not document any gross neuropathological changes. Golgi analysis of neocortical dendritic spine morphology extended our previous observations of immature, long, tortuous spines in one adult case of fraX (Rudelli, et al., Acta Neuropathologica 67:289-295, 1985) to 2 new cases. Evidence for similar dendritic spine abnormalities was found, although Golgi analysis was less than optimal because of incomplete dendritic stain impregnation. Neocortical intra-layer cell density was also investigated in all 3 cases. Cresyl violet stained neurons were counted in 10 randomly selected fields in neocortical layers II-VI of cingulate and temporal association areas (Brodmann's areas 23 and 38). Neuron counts in fraX and control neocortex showed no significant differences. Thus, abnormal dendritic spine morphology with preservation of neuronal density appears to characterize the neocortex in individuals with this common form of mental retardation.

Adolescent↗
PubMed1991

Simultaneous expression of the rare and common fragile sites on the X chromosome.

The fragile X [fra(X)] syndrome is the most common inherited form of X-linked mental retardation and is associated with a rare folate sensitive fragile site on the X chromosome at band Xq27.3. Recently, a common fragile site located at chromosome band Xq27.2 was delineated (Sutherland & Baker 1990). In order to confirm the previous findings and to further investigate the conditions required for induction of both types of fragile sites, we studied the use of four experimental protocols. Samples from a control male, two fra(X) males and a fra(X) carrier female were studied. Both common and rare fragile sites were seen in the samples from the fra(X) subjects. Up to 4% of cells showed both common and rare fragile sites on the same X chromosome at the 500 band level. The rare and common fragile sites on the X chromosome could be clearly distinguished. From 1 to 3% of the control cells exhibited the common fragile site, while none exhibited the rare fragile site. These protocols should be useful in resolving questionable fra(X) syndrome diagnoses.

Aphidicolin↗
PubMed1991

Clinical and molecular genetic study of a large German kindred with Gerstmann-Sträussler-Scheinker syndrome.

We have verified, by full open reading frame sequencing, the presence of an amino-acid-altering mutation in codon 102 of the scrapie amyloid protein gene in three affected members of a large and well-documented German family with experimentally transmitted Gerstmann-Sträussler-Scheinker syndrome. In addition, we identified the mutation by partial sequencing or DNA restriction enzyme analysis in three of 12 presently healthy family members with an affected parent, and none of 12 members without an affected parent. Thus, a total of six of 15 family members at risk for the disease (including the three established cases) had the same codon 102 mutation, a proportion consistent with the autosomal dominant inheritance pattern of disease expression. It is undetermined whether the mutation influences susceptibility to infection by an exogenous agent or is itself a proximate cause of disease.

Adult↗
PubMed1991

Molecular markers of fragile X: recent research developments.

Linkage studies are a powerful method for studying the inheritance of a genetic locus such as the fra(X) mutation where variable penetrance is present. These studies are dependent on the informativeness and availability of flanking DNA probes. Until 1989, no probes had been identified which detected loci closer than about 5 recom- bination units away from the fra(X) mutation. However, now at least four loci are known and the methods that have been employed to identify these probes will certainly lead to the identification of many more new probes that are in the immediate neighborhood of the fra(X) mutation. Progress in the characterization of such closely flanking probes should rapidly lead to a molecular understanding of the nature of the fra(X) mutation.

Chromosome Mapping↗