Isolation and chromosomal localization of unique DNA sequences from a human genomic library.

Recombinant bacteriophage lambda from a human genomic library were screened to indentify human DNA inserts having only unique sequences. Unique human inserts were found in about 1% of the phage screened. One recombinant phage, P3-2, was studied in detail. It contains a human insert of 14.7 kilobases with four internal EcoRI cleavage sites. A restriction map was constructed for EcoRI and BamHI sites. Hybridization of the 32P-labeled P3-2 probe to a Southern blot of EcoRI-digested total human DNA yielded distinct bands at positions corresponding to the human insert fragments contained in P3-2. By using a series of human-Chinese hamster somatic cell hybrids containing unique combinations of human chromosomes, the human DNA segment in phage P3-2 was assigned to human chromosome 22 by blot hybridization and synteny analysis. In addition, another human DNA segment, 11.4 kilobases, in phage P3-10 was assigned to human chromosome 10 by similar procedures. With this approach, more unique DNA sequences can be isolated, assigned to specific human chromosomes, and used as genetic markers for gene mapping and linkage, polymorphism, and other genetic studies in the human genome.     

Specific cloning of DNA fragments absent from the DNA of a male patient with an X chromosome deletion.

A method that allows the specific cloning of DNA fragments absent from patients homozygous or hemizygous for chromosomal deletions is described. The method involves phenol-accelerated competitive DNA reassociation and subsequent molecular cloning of appropriately reassociated molecules. The deletion DNA sample utilized in the competition was isolated from a patient with a minute interstitial deletion in the short arm of the X chromosome. Sheared DNA isolated from a male child, who was diagnosed as having Duchenne muscular dystrophy, chronic granulomatous disease, and retinitis pigmentosa, was combined in a 200-fold excess with Mbo I-cleaved DNA isolated from a 49, XXXXY human lymphoid cell line, and the mixture was subjected to a phenol-enhanced reassociation technique. Analysis of 81 unique segments derived from cloned reassociated DNA molecules has led to the identification of 4 (5%) human DNA fragments that are absent from the male patient's DNA. The 4 clones were localized, on the basis of hybridization with restriction nuclease-digested genomic DNA from a panel of human and human-rodent hybrid cell lines, into three regions surrounding band 21 of the short arm of the normal human X chromosome. These clones are potential linkage markers for the diseases affecting this boy. Each clone, as well as others obtainable by this approach, may also serve as a starting point in the eventual cloning of these three X-linked-disease loci. Extension of this approach to other loci, including human tumors potentially homozygous for small deletions, should also be possible.     

A heteroplasmic mitochondrial DNA 3310 mutation in the ND1 gene in a patient with type 2 diabetes, hypertrophic cardiomyopathy, and mental retardation.

A mentally retarded 57-year-old Japanese man with maternally-inherited type 2 diabetes was found to have hypertrophic cardiomyopathy (HCM) that was associated with pathological changes in the myocardial mitochondria. The mitochondrial DNA (mtDNA) of this patient was examined and a C3310 T mutation was found in the ND1 gene, which resulted in the substitution of serine for proline. The normal 3310 mtDNA band could not be detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in mtDNA from his myocardium, pancreas, cerebral tissue, skeletal muscle, and lymphocytes. However two clones sequenced from his pancreatic tissue did not show this C3310 T mutation while forty-eight did. Mitochondria isolated from the lymphocytes of his two sisters also had this mutation. mtDNA point mutations in the ND1 gene region reported thus far have been mostly homoplasmic. However, the C3310 T point mutation that was found in this patient was heteroplasmic, which is a high level of mutation and may represent the pathogenic gene that was responsible for causing mitochondrial disease.     

Biochemical investigations on a patient with a defect in cytosolic acetoacetyl-CoA thiolase,associated with mental retardation

A severely mentally retarded boy with two normal siblings was persistently found to excrete elevated amounts of 3-hydroxybutyrate and acetoacetate. Enzyme analysis in cultured fibroblasts revealed a probable deficiency in cytosolic acetoacetyl-CoA thiolase which was about half the control activity with normal mitochondrial thiolase activities. Treatment with reduced dietary fat was initiated and a rapid reduction of the ketosis to biochemical normality was demonstrated. Shortly after initiating dietary treatment he presented with severe gastrointestinal problems and the histological features of colitis cystica superficialis. This appeared to respond to intravenous hydrocortisone therapy with an apparent complete recovery.     

Altered synaptic plasticity in a mouse model of fragile X mental retardation

Fragile X syndrome, the most common inherited form of human mental retardation, is caused by mutations of the Fmr1 gene that encodes the fragile X mental retardation protein (FMRP). Biochemical evidence indicates that FMRP binds a subset of mRNAs and acts as a regulator of translation. However, the consequences of FMRP loss on neuronal function in mammals remain unknown. Here we show that a form of protein synthesis-dependent synaptic plasticity, long-term depression triggered by activation of metabotropic glutamate receptors, is selectively enhanced in the hippocampus of mutant mice lacking FMRP. This finding indicates that FMRP plays an important functional role in regulating activity-dependent synaptic plasticity in the brain and suggests new therapeutic approaches for fragile X syndrome.     

A new familial syndrome characterized by pigmentary retinopathy, hypogonadism, mental retardation, nerve deafness and glucose intolerance.

Torulopsis glabrata, an opportunistic pathogen, was found to be the etiologic agent of infections in patients with cancer. This observation prompted a retrospective review to determine the incidence and underlying factors of infection with this organism. This study showed that T. glabrata had been cultured frequently and that the incidence of infection has been progressively increasing. During a 48-month period (9/70-8/74), T. glabrata was cultured from routine surveillance and diagnostic cultures in 167 patients, 27 of whom had either presumed or documented infection. Review of clinical and necropsy records implicated T. glabrata infections as a contributory factor in the death of 14 of the 27 patients. Etiologic diagnosis of infection was established antemortem in only three patients. Pulmonary isolation in pure growth occurred in 24 of the 27 patients. Seventeen of 19 infected patients who had prior routine surveillance cultures were colonized prior to infection. Infection occurred in the setting of far advanced malignancy or leukopenia and followed the use of systemic, broad spectrum antibiotics. T. glabrata is a frequently overlooked opportunistic pathogen which, in the proper setting, appears to be producing increasing numbers of infections.     

Isolation of the human chromosomal band Xq28 within somatic cell hybrids by fragile X site breakage.

The chromosomal fragile-site mapping to Xq27.3 is associated with a frequent form of mental retardation and is prone to breakage after induced deoxyribonucleotide pool perturbation. The human hypoxanthine phosphoribosyltransferase (HPRT) and glucose-6-phosphate dehydrogenase (G6PD) genes flank the fragile X chromosome site and can be used to monitor integrity of the site in human-hamster somatic cell hybrids deficient in the rodent forms of these activities. After induction of the fragile X site, negative selection for HPRT and positive enrichment for G6PD resulted in 31 independent colonies of HPRT-,G6PD+ phenotype. Southern blot analysis demonstrated the loss of all tested markers proximal to the fragile X site with retention of all tested human Xq28 loci in a majority of the hybrids. In situ hybridization with a human-specific probe demonstrated the translocation of a small amount of human DNA to rodent chromosomes in these hybrids, suggesting chromosome breakage at the fragile X site and the subsequent translocation of Xq28. Southern blot hybridization of hybrid-cell DNA, resolved by pulsed-field gel electrophoresis, for human-specific repetitive sequences revealed abundant CpG-islands within Xq28, consistent with its known gene density. The electrophoretic banding patterns of human DNA among the hybrids were remarkably consistent, suggesting that fragile X site breakage is limited to a relatively small region in Xq27-28. These somatic cell hybrids, containing Xq27.3-qter as the sole human DNA, will aid the search for DNA associated with the fragile X site and will augment the high resolution genomic analysis of Xq28, including the identification of candidate genes for genetic-disease loci mapping to this region.     

Linkage of the Wiskott-Aldrich syndrome with polymorphic DNA sequences from the human X chromosome.

The Wiskott-Aldrich syndrome (WAS) is one of several human immunodeficiency diseases inherited as an X-linked trait. The location of WAS on the X chromosome is unknown. We have studied 10 kindreds segregating for WAS for linkage with cloned, polymorphic DNA markers and have demonstrated significant linkage between WAS and two loci, DXS14 and DXS7, that map to the proximal short arm of the X chromosome. Maximal logarithm of odds (lod scores) for WAS-DXS14 and WAS-DXS7 were 4.29 (at theta = 0.03) and 4.12 (at theta = 0.00), respectively. Linkage data between WAS and six marker loci indicate the order of the loci to be (DXYS1-DXS1)-WAS-DXS14-DXS7-(DXS84-OTC). These results suggest that the WAS locus lies within the pericentric region of the X chromosome and provide an initial step toward identifying the WAS gene and improving the genetic counseling of WAS families.     

Isolation of a herpesvirus-specific DNA polymerase from tissues of an American patient with Burkitt lymphoma.

A DNA polymerase (DNA nucleotidyltransferase) has been partially purified from a neck mass of an American patient with Burkitt lymphoma and separated from the cellular DNA polymerases. The molecular weight of the enzyme was approximately 90,000. The enzyme differs from the cellular DNA polymerases, but resembles herpes-virus-induced DNA polymerase in its primer template preference, high monovalent cation requirement for activity, and sensitivity to phosphonoacetate. Enzyme activity was inhibited specifically by an antibody directed against herpes-simplex-virus-induced DNA polymerase but not by antibodies directed against DNA polymerase alpha of HeLa cells and DNA polymerase gamma of a normal human lymphoblast cell line, NC37. Although serum of the patient with Burkitt lymphoma contained high Epstein-Barr virus titer, addition of the serum to the assay mixture did not have any effect on the activity of Burkitt lymphoma DNA polymerase. Tissues from spleen and liver of the patient with Burkitt lymphoma did not contain the herpes-virus-induced DNA polymerase. Detection of the herpes virus polymerase in the Burkitt lymphoma tissue provides additional evidence for the association of Epstein-Barr virus with this malignancy.     

Recovery from deafness in a patient with Muckle-Wells syndrome treated with anakinra

Muckle-Wells syndrome (MWS) is a dominantly inherited autoinflammatory disease characterized by rashes, fever, arthralgia, sensorineural deafness, and the possible development of systemic AA amyloidosis. We used anakinra to treat a 22-year-old patient with MWS who had deafness and a high serum level of C-reactive protein (CRP). Following treatment with anakinra, the patient's CRP level normalized, and she recovered from deafness. The fact that this occurrence has never been previously reported strengthens the role of anakinra in MWS but also raises new questions about the physiopathology of such deafness.     

Native valve endocarditis due to Pseudomonas mendocina in a patient with mental retardation and a review of literature

Pseudomonas mendocina, a Gram-negative non-fermentative rod, occurs in water and soil but is rarely recovered as a human pathogen. We report a native valve endocarditis due to Pseudomonas mendocina in a patient with mental retardation.     

A novel 7301-bp deletion in mitochondrial DNA in a patient with Kearns-Sayre syndrome, diabetes mellitus, and primary amenorrhoea.

We report a 27-year-old woman with a form of mitochondrial myopathy including chronic progressive external opthalmoplegia, retinal pigmentary dystrophy, cerebellar ataxia, and cardiac conduction block (Kearns-Sayre syndrome). At age 13 years a cardiac pacemaker was implanted. She also had sensineural hearing loss, delayed puberty, and primary amenorrhoea. She was weelchair-bound since the age of 20 years. At age 27, insulin-dependent diabetes mellitus and osteoporosis were diagnosed. Insulin treatment was started and associated endocrinopathies were investigated. DNA analysis identified a novel 7301-bp deletion in mitochondrial DNA, ranging from position 6530 to 13 831 corroborating the diagnosis of Kearns-Sayre syndrome.     

Altered mRNA transport,docking, and protein translation in neurons lacking fragile X mental retardation protein

Fragile X syndrome is caused by the absence of functional fragile X mental retardation protein (FMRP), an RNA binding protein. The molecular mechanism of aberrant protein synthesis in fmr1 KO mice is closely associated with the role of FMRP in mRNA transport, delivery, and local protein synthesis. We show that GFP-labeled Fmr1 and CaMKIIα mRNAs undergo decelerated motion at 0–40 min after group I mGluR stimulation, and later recover at 40–60 min. Then we investigate targeting of mRNAs associated with FMRP after neuronal stimulation. We find that FMRP is synthesized closely adjacent to stimulated mGluR5 receptors. Moreover, in WT neurons, CaMKIIα mRNA can be delivered and translated in dendritic spines within 10 min in response to group I mGluR stimulation, whereas KO neurons fail to show this response. These data suggest that FMRP can mediate spatial mRNA delivery for local protein synthesis in response to synaptic stimulation.     

Increased rates of cerebral glucose metabolism in a mouse model of fragile X mental retardation

In humans, failure to express the fragile X mental retardation protein (FMRP) gives rise to fragile X syndrome, the most common form of inherited mental retardation. A fragile X knockout (fmr1 KO) mouse has been described that has some of the characteristics of patients with fragile X syndrome, including immature dendritic spines and subtle behavioral deficits. In our behavioral studies, fmr1 KO mice exhibited hyperactivity and a higher rate of entrance into the center of an open field compared with controls, suggesting decreased levels of anxiety. Our finding of impaired performance of fmr1 KO mice on a passive avoidance task is suggestive of a deficit in learning and memory. In an effort to understand what brain regions are involved in the behavioral abnormalities, we applied the [(14)C]deoxyglucose method for the determination of cerebral metabolic rates for glucose (CMR(glc)). We measured CMR(glc) in 38 regions in adult male fmr1 KO and WT littermates. We found CMR(glc) was higher in all 38 regions in fmr1 KO mice, and in 26 of the regions, differences were statistically significant. Differences in CMR(glc) ranged from 12% to 46%, and the greatest differences occurred in regions of the limbic system and primary sensory and posterior parietal cortical areas. Regions most affected are consistent with behavioral deficiencies and regions in which FMRP expression is highest. Higher CMR(glc) in fragile X mice may be a function of abnormalities found in dendritic spines.     

Isolation and characterization of DNA sequences amplified in multidrug-resistant hamster cells.

The mechanism by which mammalian cells acquire resistance to chemotherapeutic agents has been investigated by using molecular genetic techniques. LZ and C5, two independently derived multidrug-resistant Chinese hamster cell lines, share specific amplified DNA sequences. We demonstrate that commonly amplified DNA sequences reside in a contiguous domain of approximately equal to 120 kilobases (kb). We report the isolation of this DNA domain in cosmid clones and show that the level of amplification of the domain is correlated with the level of resistance in multidrug-resistant cell lines. The organization of the amplified domain was deduced by a unique approach utilizing in-gel hybridization of cloned DNA with amplified genomic DNA. We show that the entire cloned region is amplified in adriamycin-resistant LZ cells and independently derived, colchicine-resistant C5 cells. A mRNA species of approximately equal to 5 kb is encoded by a gene located within the boundaries of this region. Genomic sequences homologous to the 5-kb mRNA span over 75 kb of the amplified DNA segment. The level of expression of this mRNA in multidrug-resistant cells is correlated with the degree of gene amplification and the degree of drug resistance. Our results strongly suggest that the 5-kb mRNA species plays a role in the mechanism of multidrug resistance common to the LZ and C5 cell lines.     

Genetic analysis of the fragile-X mental retardation syndrome with two flanking polymorphic DNA markers.

The fragile-X mental retardation syndrome, one of the most prevalent chromosome X-linked diseases (approximately equal to 1 of 2000 newborn males), is characterized by the presence in affected males and in a portion of carrier females of a fragile site at chromosomes band Xq27. We have performed a linkage analysis in 16 families between the locus for the fragile-X syndrome, FRAXQ27, and two polymorphic DNA markers that correspond to the anonymous probe St14 and to the coagulation factor IX gene F9. Our results indicate that the order of loci is centromere-F9-FRAXQ27-St14-Xqter. The estimate of the recombination fraction for the linkage F9-FRAXQ27 is 0.12 (90% confidence limits: 0.044-0.225) and 0.10 for FRAXQ27-St14 (90% confidence limits: 0.040-0.185). Recombination between St14 and F9 does not appear to be significantly different in normal and fragile-X families. The two flanking probes were used for diagnosis of the carrier state and for detection of transmission of the disease through phenotypically normal males. They should also allow first-trimester diagnosis with a reliability of about 98% in 40% of the families. Used in conjunction with the cytogenetic analysis, the segregation studies with both probes should improve the genetic counseling for the fragile-X syndrome and should be useful for the formal genetic analysis of this unique disease.     

Diabetes mellitus, deafness, muscle weakness and hypocalcemia in a patient with an A3243G mutation of the mitochondrial DNA

In a 54-year-old woman with diabetes mellitus, hearing loss, muscle weakness and hypocalcemia, caused by idiopathic hypoparathyroidism, an A to G transition at the nucleotide position of 3243 (A3243G mutation) was found in the mitochondrial DNA from her leukocytes. Clinical features of diabetes mellitus and hearing loss in association with the A3243G mutation are compatible with a diagnosis of maternally inherited diabetes and deafness (MIDD). Although hypoparathyroidism is rarely seen in MIDD, we consider that hypoparathyroidism in this patient is a possible phenotype caused by the A3243G mutation of mitochondrial DNA.     

Mitochondrial DNA deletion diagnosed by analysis of an endomyocardial biopsy specimen from a patient with Kearns-Sayre syndrome and complete heart block.

Defects of mitochondrial DNA have been found at necropsy in the myocardium of patients with Kearns-Sayre syndrome. A patient with characteristics typical of Kearns-Sayre syndrome and a complete heart block is described. Southern blot analysis showed a deletion of 3.3 kb in the mitochondrial DNA in an endomyocardial biopsy specimen and in skeletal muscle. The deletion led to the disappearance of the genes for four transfer RNAs and four subunits of complex I (NADH:ubiquinone oxidoreductase) in the mitochondrial respiratory chain. The defect could not be demonstrated in whole blood despite amplification of the mitochondrial DNA region of interest by the polymerase chain reaction technique. There can be heteroplasmy--that is, normal and abnormal mitochondrial DNA populations in one cell--in different tissues, and the degree of heteroplasmy may be crucial in the development of organ-specific symptoms. This patient raises the possibility that some tissues can be specifically enriched with mitochondria with DNA defects and emphasises the need for elective sampling of the target tissue and polymerase chain reaction technique to exclude these defects. The role of mitochondrial DNA defects in idiopathic cardiomyopathies could perhaps be studied by analysis of mitochondrial DNA from endomyocardial biopsy specimens.