Genomewide homozygosity mapping and molecular analysis of a candidate gene located on 22q13 (fibulin-1) in a previously undescribed vitreoretinal dystrophy

OBJECTIVES To localize the gene that causes an autosomal recessively inherited vitreoretinal dystrophy that has not been described, to our knowledge, and to analyze a candidate gene mapped to 22q13 (fibulin-1 [FBLN1]). METHODS Homozygosity mapping with 500 microsatellite markers spread over the whole genome (mean distance, 7.2 centimorgans [cM]) and mutation analysis of the complete coding region of FBLN1. RESULTS Homozygosity for all analyzed markers was found in the 4 affected siblings in a region on chromosome 22 encompassing 12 cM from D22S444 (centromeric) to D22S1170 (telomeric). Lod scores were between 0.017 and 2.36 (theta = 0). A mutation analysis of the complete coding region of FBLN1, which encodes interacting extracellular matrix proteins, revealed 4 previously undescribed single nucleotide polymorphisms. CONCLUSIONS A genomewide homozygosity mapping analysis supported the hypothesis that the gene responsible for a unique vitreoretinal dystrophy is located on chromosome 22q13. No obviously pathogenic mutation was found in the candidate gene, FBLN1

Tissue-specific expression of a FMR1/β-galactosidase fusion gene in transgenic mice

Fragile X syndrome is one of the most common genetic causes of mental retardation, yet the mechanisms controlling expression of the fragile X mental retardation gene FMR1 are poorly understood. To identify sequences regulating FMR1 transcription, transgenic mouse lines were established using a fusion gene consisting of an E.coli β-galactosidase reporter gene (lacZ) linked to a 2.8 kb fragment spanning the 5′-region of FMR1. Five transgenic mouse lines showed lacZ expression in brain, in particular in neurons of the hippocampus and the granular layer of the cerebellum. Expression of the reporter gene was also detected in Leydig cells and spermatogonia in the testis, in many epithelia of adult mice, and in the two other steroidogenic cell types, adrenal cortex cells and ovarian follicle cells. Embryonic tissues which showed strong activity of the reporter gene included the telencephalon, the genital ridge, and the notochord. This expression pattern closely resembles the endogenous one, indicating that the 5′ FMR1 gene promoter region used in this study contains most cis-acting elements regulating FMR1 transcriptio

Uniparental disomy 7 in Silver—Russell syndrome and primordial growth retardation

Maternal uniparental disomy for the entire chromosome 7 has so far been reported in three patients with intrauterine and postnatal growth retardation. Two were detected because they were homozygous for a cystic fibrosis mutation for which only the mother was heterozygous, and one because he was homozygous for a rare COL1A2 mutation. We investigated 35 patients with either the Silver-Russell syndrome or primordial growth retardation and their parents with PCR markers to search for uniparental disomy 7. Four of 35 patients were found to have maternal disomy, including three with isodisomy and one with heterodisomy. The data confirm the hypothetical localization of a maternally imprinted gene (or more than one such gene) on chromosome 7. It is suggested to search for UPD 7 in families with an offspring with sporadic Silver-Russell syndrome or primordial growth retardatio

Das Human-Genom-Projekt: Die Entschlüsselung des menschlichen Erbmaterials

The ambitious plan of the determination of the DNA sequence of the human genome is known as the human genome project (HGP). Since its start in 1991, it has yielded significant results. Until recently, the work has focused on the establishment of high-resolution genetic and physical maps. The genome sequences of many prokaryotes and of several eukaryotes have been completely determined. Approximately 17% of the human genome sequence are already known, and recent technological developments will lead to the determination of the complete human genome sequence by the years 2000-2003. At the moment, the genomic location and at least partial sequence of 30.000 human genes are known, corresponding to approximately 30% of all human genes. These results are relevant for the localisation and isolation of disease genes and disease susceptibility alleles. The knowledge of a large part of all human genes allows the determination of the activity of many thousands of genes in parallel. The information from the HGP makes the search for frequent predisposition alleles for common diseases (cancer, heart disease, psychiatric diseases) possible, in particular through the identification of linkage disequilibria. These studies require the clinical and genetic analysis of large human populations in hitherto unknown detail, thereby raising new questions regarding the ownership and the privacy of genetic data

Erbliche Schwerhörigkeit: neue Möglichkeiten der Diagnostik

Mutations in many different genes can result in hearing loss. Using different molecular genetic methods, the disease-causing gene mutations can often be identified or at least localised to defined regions of the genome. These new diagnostic possibilities result from the localisation and identification of a number of hearing-loss genes in the last five years. Diagnostic investigations should always be accompanied by a genetic counselling of the family. In addition, the isolation thus far of 11 genes mutated in autosomal dominant inherited hearing loss, as well as of 6 genes mutated in autosomal recessive inherited hearing loss, has contributed to a better understanding of the molecular pathology of hearing loss in general. However, we are only beginning to see the whole picture, as an estimated 50 to 80 hearing loss genes remain to be discovered

Angeborene Innenohrschwerhörigkeit durch Mutationen im Connexin-26-Gen

Hearing loss is a frequent disease with an estimated incidence of 1:1000 in children. Hereditary hearing loss is characterised by enormous genetic heterogeneity, which makes diagnosis difficult. Approximately 50% of the Caucasian patients with autosomal recessive inherited hearing loss carry mutations in the connexin- 26 gene on chromosome 13. Standard screening procedures such as SSCP (single strand conformation polymorphism) analysis, DHPLC (denaturing high performance liquid chromatography) and subsequent sequencing are used to investigate this gene. A genetic test is thus available which can be offered to probands in genetic counselling. We investigated 11 patients with hearing loss and found sequence aberrations in 7 patients, which is causative for the hearing loss in at least 5 patients. The first application of DHPLC in Switzerland is also documented

Direct genetic diagnosis in Huntington's chorea

Huntington's disease is a late manifesting autosomal dominant neurodegenerative disorder. It is characterized by motor disturbance, loss of cognitive functions and psychiatric manifestations. Recently, the disease causing mutation, an unstable DNA sequence in the coding region of the Huntington gene on chromosome 4p, has been identified. A trinucleotide (CAG) repeat is expanded over the normal range and can easily be detected by standard laboratory methods. Accurate genetic testing can now be offered in clinically questionable cases and to subjects at risk for Huntington's disease. Furthermore, there seems to be a correlation between the size of the expanded CAG repeat and the age of onset in affected individuals. We have investigated more than 130 individuals from different affected families and illustrate the advantages and the clinical application of the new method

A novel MSP/DHPLC method for the investigation of the methylation status of imprinted genes enables the molecular detection of low cell mosaicisms

We describe a new procedure for the analysis of the methlyation status of imprinted genes based on methylation-specific PCR followed by denaturing high performance liquid chromatography (MSP/DHPLC). The method offers a rapid and very reliable alternative to conventional methods used for such purposes such as Southern blots and methylation specific PCR (allele-specific MSP). The efficient resolution of the differentially methylated alleles is demonstrated for two human imprinted genes, namely the SNRPN gene and the LIT1 gene (KCNQ1OT1). Abnormal imprinting of the two genes is associated with the Angelman/Prader-Willi syndromes and the Beckwith-Wiedemann syndrome, respectively. The MSP/DHPLC method is based on PCR amplification of gene segments which show parent-of-origin specific methylation. Genomic DNA is subjected to an in vitro bisulfite treatment prior to PCR amplifications using primers specific for modified DNA. Both alleles are theoretically amplified with equal efficiency and are represented by identically sized PCR products; they differ, however, at a number of positions within the amplified DNA segment. The DHPLC analysis allows a very efficient resolution of the two populations of PCR products. The high sensitivity and quantitative properties of the MSP/DHPLC method are illustrated based on its ability to reveal a low cell mosaicism in an infant with a maternal uniparental disomy 15 (i.e., Prader-Willi syndrome patient). The minor cell line (approximately 8% in blood) was not detectable with conventional molecular analysis. While the detection of low cell mosaicisms of structurally abnormal chromosomes usually relies on cytogenetic studies, the MSP/DHPLC method described here not only offers an alternative at the molecular level, but may also reveal mosaicisms concerning structurally intact chromosomes

A new stable alpha chain variant : Hb Basel [alpha14(A12)Trp--<Leu (alpha1)]

We describe a heterozygosity for a new missense mutation on the alpha1-globin gene of an 18-year-old woman of Portuguese ancestry with severe hypochromic anemia and iron deficiency. Hemoglobin (Hb) analysis by high performance liquid chromatography (HPLC) found a prominent peak constituting about 12% of total Hb. Sequencing of the globin genes of the index patient found the mutation alpha14(A12)Trp--T. We identified the same mutation in blood and DNA of the mother, which provides evidence that the variant is stable and does not have direct pathophysiological or hematological consequences