Corinne D. Boehm

Molecular characterization of seven beta-thalassemia mutations in Asian Indians.

To characterize systematically the mutations which produce beta‐thalassemia in Asian Indians, we first determined the DNA polymorphism haplotype in the beta‐globin gene cluster of 44 beta‐thalassemia chromosomes in the ethnic group. Nine different haplotypes were observed. Upon molecular cloning and partial DNA sequencing of one beta‐gene from each of eight haplotypes and two from the ninth, seven different mutations were found. None of these have been identified in Mediterranean patients, even among the five haplotypes which appeared identical in the two groups. Asian Indian mutations included one nonsense and three frameshift mutations, one deletion affecting an acceptor splice site, and two mutations affecting a donor splice site. The correlation of a specific mutation with a specific haplotype was high but not invariant. Two mutations were associated with more than one haplotype but, in each instance, the mutation spread to a new haplotype could be explained most simply by recombination 5′ to the beta‐globin gene. In addition, four mutations, one reported here and three others previously reported, have been observed on two chromosome backgrounds that are identical except for the status of a polymorphic HinfI site 5′ to the beta gene. This HinfI site does not show significant linkage disequilibrium with markers both 5′ and 3′ to it, suggesting that it lies within a region of relative sequence randomization.

Improved detection of the sickle mutation by DNA analysis: application to prenatal diagnosis.

DETECTION of sickle hemoglobin in the human fetus was first accomplished nearly 10 years ago.1 , 2 This marked the beginning of a technology for prenatal diagnosis of the hemoglobinopathies. When m...

New Tools for Mendelian Disease Gene Identification: PhenoDB Variant Analysis Module; and GeneMatcher, a Web-Based Tool for Linking Investigators with an Interest in the Same Gene

Identifying the causative variant from among the thousands identified by whole‐exome sequencing or whole‐genome sequencing is a formidable challenge. To make this process as efficient and flexible as possible, we have developed a Variant Analysis Module coupled to our previously described Web‐based phenotype intake tool, PhenoDB (http://researchphenodb.net and http://phenodb.org). When a small number of candidate‐causative variants have been identified in a study of a particular patient or family, a second, more difficult challenge becomes proof of causality for any given variant. One approach to this problem is to find other cases with a similar phenotype and mutations in the same candidate gene. Alternatively, it may be possible to develop biological evidence for causality, an approach that is assisted by making connections to basic scientists studying the gene of interest, often in the setting of a model organism. Both of these strategies benefit from an open access, online site where individual clinicians and investigators could post genes of interest. To this end, we developed GeneMatcher (http://genematcher.org), a freely accessible Website that enables connections between clinicians and researchers across the world who share an interest in the same gene(s).

Practical guide to the diagnosis of thalassemia

Thalassemias occur in individuals of all ethnic backgrounds and are among the most common genetic diseases worldwide. The diagnosis of thalassemia can easily be part of primary medical practice. Here we outline a practical approach to the detection of thalassemias in three common clinical settings. The first involves any patient with a low mean corpuscular volume (MCV) with or without anemia. The second is a neonatal screening result indicating possible presence of thalassemia. Finally, evaluation for thalassemia should be considered in the context of family planning or pregnancy in patients whose ethnicity indicates origin from high risk geographic areas. We also review the various types of the thalassemia syndromes and provide an overview of general therapeutic considerations.

Gene Defects in β-Thalassemia and Their Prenatal Diagnosis

In contrast to a-thalassemia, P-thalassemia is generally caused by point mutations. These mutations were studied extensively from 1980 to 1986, usually by haplotype analysis of the P-globin gene cluster followed by cloning and sequencing of the mutant P-globin gene. About 40 point mutations producing P-thalassemia were discovered by mid-1987, and many were documented by transient expression studies of the mutant gene. In 1987 it became possible to amplify regions of the P-globin gene starting with genomic DNA from leukocyte^^^^ and to sequence directly the amplified p r o d u ~ t s . ~ , ~ By use of this approach in selected individuals known to lack the common alleles of the ethnic group represented by the patient under study, about 50 more alleles have been characterized in less than 2 years.6 In July 1990, the total number of point mutations which produce P-thalassemia known to the authors is 91 (TABLE 1 and FIG. 1). Since the total number of P-globin alleles known to produce any clinical phenotype is roughly 200, the P-thalassemia alleles now account for over 45% of the clinically significant alleles at the P-globin locus, and the abnormal hemoglobins account for the remainder. The spectrum of P-thalassemia alleles has been determined in a wide variety of population groups, including American blacks,,* Asian Indians,, Italians and Greeks, Spanish, Turks, Kurdish Jews,14 Chine~e , ~ . ~ Japane~e , ~ and Thai, among others. In most affected population groups, such as Mediterranean peoples, Chinese and Southeast Asians, Asian Indians, and blacks of African origin, a handful of ethnic-group-specific alleles accounts for roughly 90-93% of P-thalassemia genes. For example, among Chinese from Kuontung province, 4 alleles account for about 90% of p-thalassemia genes. On the other hand, a large number of rarer alleles have been observed in each ethnic group. For example, to date 11 rare alleles account for the remaining 10% of P-thalassemia genes in Chinese. The total number of mutations obscrvcd in the well-studied groups is, in Chinese, 15; Asian Indians, 10; blacks, 12; Mediterraneans, 31. In the broad group of Mediterranean peoples it is important to note that although many of the 31 alleles have been observed in diverse regions of the Mediterranean basin, allele frequencies vary greatly from one country to another. Because so many alleles are found in each region, most individuals with P-thalassemia major carry two different alleles and are called genetic compounds.

Familial neurofibromatosis type 1: Clinical experience with DNA testing

To determine how DNA testing for familial neurofibromatosis type 1 (NF-1) would be used in a clinical setting by patients and physicians, we performed confirmatory DNA testing on 24 individuals with a family history of NF-1 and on nine couples who requested DNA testing for current or future prenatal diagnosis. A further eight families were unsuitable for DNA linkage testing because of their pedigree structure. For the majority of persons the certainty of the test result was 95% to 99%. In five individuals, only one of whom was less than 6 years of age, the DNA-based diagnosis was discrepant with the clinical diagnosis at the time of referral. In all five cases, results of subsequent clinical re-examinations were consistent with the DNA diagnosis. We conclude that DNA testing by linkage analysis may be most useful as an adjunct to the clinical diagnosis of familial NF-1 (1) in children less than 6 years of age in whom the full manifestations may not yet be apparent, (2) in NF-1 families interested in prenatal testing, and (3) when the resources available for a complete clinical examination are limited.

Prenatal detection of an unstable ring 21 chromosome

SummaryAn unstable ring chromosome 21 detected through prenatal studies was associated at birth with an apparently normal male phenotype. At 14 months of age, examination indicated only minor developmental delay. The majority of cells examined from amniocyte, fibroblast, and lymphocyte cultures contained an asymmetrical dicentric ring 21 chromosome which was larger than a normal chromosome 21. This ring is presumed to be a duplication for most of chromosome 21 and a deletion of part of the terminal regions. The karyotype is described as mos45, XY,-21/46,XY,r(21)(p13q22.3). The child is monosomic for part of the sub-band 21q22.3 in every cell and trisomic for the remainder of the chromosome in most of his cells. The terminal deletion does not appear to have been severely detrimental to the phenotype and the effective trisomy present in many cells studies was insufficient to cause the Down syndrome.

Neurobehavioral Effects of the Fragile X Premutation in Adult Women: A Controlled Study

Although previous studies have suggested that the fragile X premutation (fra [X] pM) does not cause deleterious effects, methodological constraints have prevented more definitive conclusions from being reached. In this report, we describe the neuropsychiatric and cognitive-neuropsychological status of 34 adult women with the fra (X) pM, as compared with a well-matched control group of 41 mothers of fra (X)-negative children with developmental disability. The results indicate that there are no meaningful differences between adult women with the fra (X) pM and control subjects with respect to cognitive abilities or profile, neuropsychological function, psychiatric diagnoses or symptoms, and self-rated personality profile. No measure for either group showed evidence of functioning outside the normal range except for a high lifetime prevalence of major depression in both groups. Additional exploratory analyses within the fra (X) group showed no significant effect of either the size of the fra (X) insert or X chromosome inactivation pattern in leukocytes, on any measure of neurobehavioral function. These findings provide additional information to professionals providing genetic counseling to, and assessment of, fra (X) families.

Clinical consequences of an increasing trend of preferential use of cultured villi for molecular diagnosis by CVS

To compare the use of uncultured versus cultured villus cells for DNA‐based prenatal diagnosis.

Prenatal diagnosis of sickle cell anemia--1988.

In 1975 the first prenatal diagnoses of sickle cell anemia were accomplished by study of the @-globin chains produced in fetal red blood cells obtained by fetoscopy.’*’ Subsequently, about 50 prenatal diagnoses of sickle cell anemia were performed following fetoscopy between 1975 and 1979. In late 1978 Kan and Dozy made the seminal observation of a DNA polymorphism adjacent to the @-globin gene which tracked frequently with the