Gene redundancy and pharmacological gene therapy: implications for X-linked adrenoleukodystrophy

As more functional redundancy in mammalian cells is discovered, enhanced expression of genes involved in alternative pathways may become an effective form of gene therapy. X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal disorder with impaired very-long-chain fatty acid metabolism. The X-ALD gene encodes a peroxisomal membrane protein (ALDP) that is part of a small family of related peroxisomal membrane proteins. We show that 4-phenylbutyrate treatment of cells from both X-ALD patients and X-ALD knockout mice results in decreased levels of and increased beta-oxidation of very-long-chain fatty acids; increased expression of the peroxisomal protein ALDRP; and induction of peroxisome proliferation. We also demonstrate that ALDP and ALDRP are functionally related, by ALDRP cDNA complementation of X-ALD fibroblasts. Finally, we demonstrate the in vivo efficacy of dietary 4-phenylbutyrate treatment through its production of a substantial reduction of very-long-chain fatty acid levels in the brain and adrenal glands of X-ALD mice.

Medieval theories of mental representation

Throughout most of the Middle ages, it was generally held that stored mental representations of perceived objects or events preserved the forms or species of such objects. This belief was consistent with a metaphor used by Plato. It was also consistent with the medieval belief that a number of cognitive processes took place in the ventricles of the brain and with the phenomenology of afterimages and imagination itself. In the 14th century, William of Ockham challenged this belief by claiming that mental representations are not stored but instead constructed in the basis of past learned experiences.

The force of events: cross-modality matching the recency of news events

Subjects recorded their impressions of the recency of news events by squeezing a dynamometer. This measure of recency was significantly related to the vividness of the memory for the event, when actual date was controlled for, and the relationship was stronger than that obtained when subjects wrote down their estimates of the dates. The results support the existence of distance-based processes such as inference from trace strength in our memory for when events occurred.

A rapid method for simultaneous detection of phenotypic resistance to inhibitors of protease and reverse transcriptase in recombinant human immunodeficiency virus type 1 isolates from patients treated with antiretroviral drugs

Combination therapy with protease (PR) and reverse transcriptase (RT) inhibitors can efficiently suppress human immunodeficiency virus (HIV) replication, but the emergence of drug-resistant variants correlates strongly with therapeutic failure. Here we describe a new method for high-throughput analysis of clinical samples that permits the simultaneous detection of HIV type 1 (HIV-1) phenotypic resistance to both RT and PR inhibitors by means of recombinant virus assay technology. HIV-1 RNA is extracted from plasma samples, and a 2.2-kb fragment containing the entire HIV-1 PR- and RT-coding sequence is amplified by nested reverse transcription-PCR. The pool of PR-RT-coding sequences is then cotransfected into CD4+ T lymphocytes (MT4) with the pGEMT3deltaPRT plasmid from which most of the PR (codons 10 to 99) and RT (codons 1 to 482) sequences are deleted. Homologous recombination leads to the generation of chimeric viruses containing PR- and RT-coding sequences derived from HIV-1 RNA in plasma. The susceptibilities of the chimeric viruses to all currently available RT and/or PR inhibitors is determined by an MT4 cell-3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide-based cell viability assay in an automated system that allows high sample throughput. The profile of resistance to all RT and PR inhibitors is displayed graphically in a single PR-RT-Antivirogram. This assay system facilitates the rapid large-scale phenotypic resistance determinations for all RT and PR inhibitors in one standardized assay.

The 'sports hernia': a common cause of groin pain

Athletes who participate in sports that require repetitive twisting and turning at speed, such as soccer or ice hockey, may be at risk of developing a 'sports hernia'-disruption of the inguinal canal without a clinically detectable hernia. Insidious onset of unilateral groin pain is the most common symptom. Concurrent pathologies, such as osteitis pubis and adductor tenoperiostitis, may complicate diagnosis. Plain radiographs and a bone scan can aid differential diagnosis, but herniography is not recommended. Surgery is the preferred treatment. Structured rehabilitation should enable athletes to return to sports activity 6 to 8 weeks after surgery.

Exercise induced leg pain

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Connexin32 gene mutations in X-linked dominant Charcot-Marie-Tooth disease (CMTX1)

Single-strand conformational polymorphisms (SSCP) of the connexin32 gene were analyzed in 121 patients possibly affected by Charcot-Marie-Tooth (CMT) disease. The 121 patients were selected from 443 possible CMT/HNPP (hereditary neuropathy with liability to pressure palsies) patients based on genetic linkage to Xq13.1, absence of the 17p12 duplication and deletion, and absence of point mutations in PMP22 and P0. We found five new mutations at nucleotides 105 (C-T), 316 (C-G), 321 (C-T), 328 (T-C), and 657 (G-C), and three mutations at nucleotide 126 (C-T), 249 (G-A), and 477 (G-A) previously described in other unrelated families. The nucleotide changes resulted in seven amino-acid substitutions and one premature stop codon.

Provision of clean injecting equipment

Providing clean needles and syringes to injecting drug users is one established strategy to prevent the spread of HIV and other blood borne infections ( 1 ). Our A&E department had been faced with problems from intravenous (IV) drug users requesting clean injecting equipment, and we wanted to know how other A&Es dealt with such requests, and whether they experienced similar problems.

A medieval controversy about odor

Medieval scholars debated whether odor was transmitted through a medium as suggested by Aristotle or by fumes or vapors from the odoriferous object as suggested by Plato. Key evidence believed to support Aristotle's theory was the behavior of birds in detecting carrion from far away. The medieval approach to this essentially secular controversy was, nevertheless, similar to that used in issues thinkers of that time regarded as of more importance.

Status of antithrombotic therapy for patients with atrial fibrillation in university hospitals

BACKGROUND

The risk of stroke in patients with atrial fibrillation can be significantly reduced with antithrombotic therapy. Despite this, many physicians remain hesitant to prescribe warfarin sodium or aspirin therapy for patients with atrial fibrillation.

OBJECTIVE

To assess the use of antithrombotic therapy in patients with atrial fibrillation at 6 academic hospitals in the United States.

METHODS

Records were reviewed from consecutive hospital admissions of 309 patients with atrial fibrillation at 6 members of the University Health System Consortium, Oak Brook, III, which is a member driven alliance of 70 academic health centers in the United States. Risk factors for stroke, contraindications to anticoagulant therapy, and use of antithrombotic therapy at admission and discharge were recorded.

RESULTS

The mean age of patients was 71.6 years, 54% had chronic, 22% paroxysmal, and 24% new-onset atrial fibrillation. Eighty-two percent of the patients had cardiovascular risk factors that have been associated with increased risk of stroke. At least 1 relative contraindication to anticoagulant therapy was present in 44%. At the time of admission. 32% of the patients with previously diagnosed atrial fibrillation (n = 235) were receiving warfarin (or warfarin plus aspirin), 31% were receiving aspirin alone, and 36% were receiving no antithrombotic therapy. At discharge (n = 230), 41% of these patients were taking warfarin (or warfarin plus aspirin) and 36% were taking aspirin. Forty-four percent of the patients with risk factors for stroke and no contraindications to anticoagulation (n = 134) were discharged on a regimen of warfarin (or warfarin plus aspirin), 34% were discharged on a regimen of aspirin, and 22% received no antithrombotic therapy.

CONCLUSIONS

About half of the patients with atrial fibrillation admitted to these academic hospitals had clinical risk factors that are associated with increased risk of stroke and no contraindications to anticoagulation. Antithrombotic therapy was underused in these patients.

No evidence for 'skewed' inactivation of the X-chromosome as cause of Leber's hereditary optic neuropathy in female carriers

Leber's hereditary optic neuropathy (LHON) is a maternally inherited disorder of the optic nerves. It has been proposed that the specific mutations in the mitochondrial DNA (mtDNA) that are associated with LHON require and X-chromosomally encoded permissive factor in order to become expressed. This would explain both the preponderance of male patients and the fact that most carriers of specific mtDNA mutations remain unaffected. Although linkage studies have been negative so far, the existence of such a factor has not been ruled out. We investigated the genealogical data of 24 large LHON pedigrees and concluded that the presumed X-linked factor would be recessively inherited and that at least 57% of the affected females would be heterozygous. Therefore, these females must be the victim of nonrandom X-chromosomal inactivation (skewed lyonization). However, analysis of X-chromosomal methylation patterns in 16 LHON-affected females revealed substantial skewing in only 15%-20% of cases, which is not significantly different from the patterns in 49 controls. Moreover, we found the frequency of LHON in daughters of affected heterozygous females to be twice to three times as high as in daughters of unaffected heterozygous females, which cannot be explained by an X-chromosomally inherited factor. We concluded that the results of our investigations do not support the hypothesis that LHON is a digenic disease with an X-linked factor being the main cause of loss of vision in the presence of relevant mtDNA mutations.

Association as a cause of dating bias

Two experiments investigated a dating bias in which people tend to estimate recent dates too remotely and remote dates too recently. Experiment 1 examined and upheld a prediction of the hypothesis that bias arises because events whose time of occurrence is unknown are dated through associated events for which some time information is available. Experiment 2 required some subjects to date prototype events while others dated specific events. Prototype events were dated more recently, and the errors in dating specific events were related to differences in the way the prototype events were dated. Both sets of results were predicted by the association hypothesis, according to which events whose dates are well known are dated with reference either to specific associated events or to prototype events.

ALDP expression in fibroblasts of patients with X-linked adrenoleukodystrophy

The adrenoleukodystrophy gene encodes a peroxisomal integral membrane protein (ALDP) consisting of 745 amino acids with a molecular weight of 75kDa. ALDP expression was studied in fibroblasts from 24 male ALD patients from 17 unrelated ALD kindreds. In four kindreds an identical 2-base-pair deletion was found. We report the absence of ALDP in 12 kindreds carrying nonsense mutations, frame shifts or amino acid substitutions in the carboxy terminus of ALDP, together accounting for 71% of the ALD kindreds. ALDP was present in five kindreds (29%) with amino acid substitutions in the amino terminal half of the protein; in two of these kindreds ALDP was present although at a reduced level. The absence of truncated proteins suggests that the carboxy terminus has a function in the stabilization of ALDP.

Spectrum of mutations in the gene encoding the adrenoleukodystrophy protein

X-linked adrenoleukodystrophy (ALD) has been associated with mutations in a gene encoding an ATP-binding transporter, which is located in the peroxisomal membrane. Deficiency of the gene leads to impaired peroxisomal beta-oxidation. Systematic analysis of the open reading frame of the ALD gene, using reverse transcriptase-PCR, followed by direct sequencing, revealed mutations in all 28 unrelated kindreds analyzed. No entire gene deletions or drastic promoter mutations were detected. In only one kindred did the mutation involve multiple exons. The other mutations were small alterations leading to missense (13 of 28) or nonsense mutations, a single amino acid deletion, frameshifts, or splice acceptor-site defects. Mutations affecting a single amino acid were concentrated in the region between the third and fourth putative transmembrane domains and in the ATP-binding domain. Mutations were detected in all investigated ALD kindreds, suggesting that this gene is the only gene responsible for X-linked ALD. This overview of mutations is useful in the determination of structurally and functionally important regions and provides an efficient screening strategy for identification of mutations in the ALD gene.

The gene for X-linked myotubular myopathy is located in an 8 Mb region at the border of Xq27.3 and Xq28

X-linked recessive myotubular myopathy (XLMTM) is a rare and severe neonatal neuromuscular disease characterized by muscle weakness, hypotonia, and respiratory problems. Here we report an extensive linkage analysis in two families with XLMTM. Using 18 markers in the Xq27-Xqter region we found a maximum two-point lod score of Z = 4.00 at theta = 0.00 for the marker II-10 (DXS466). Three recombinations were detected between markers and the disease locus. At the distal side of Xq27.3 a recombination was present in between RNI (DXS369) and VK23b (DXS297), another in between VK23b (DXS297) and II-10 (DXS466), and at the proximal side of Xq28 a recombination in between U6.2 (DXS304) and Cpx67 (DXS134). Combining the results of both families we conclude that XLMTM is located in the 8 Mb(11 cM) region between VK23b (DXS297) and Cpx67 (DXS134).

Identification of a two base pair deletion in five unrelated families with adrenoleukodystrophy: a possible hot spot for mutations

The gene for X-linked adrenoleukodystrophy (ALD) was recently identified. Intragenic deletions of several kilobases were found in about 7% of patients. Point mutations, expected to be very heterogeneous, were identified so far in only two patients. We report the identification of a two base pair deletion at position 1801-1802 of the ALD cDNA, located within the fifth exon of the ALD gene, which precedes the two consensus motives for ATP-binding. This microdeletion was found in five out of 40 unrelated ALD kindreds, indicating that this position is a hot spot for mutations. The mutation was observed both in patients with childhood cerebral ALD (CCALD) and in patients with adrenomyeloneuropathy (AMN).

Deletion of the serine 34 codon from the major peripheral myelin protein P0 gene in Charcot-Marie-Tooth disease type 1B

Charcot-Marie-Tooth disease type 1B (CMT1B) is genetically linked to chromosome 1q21-23. The major peripheral myelin protein gene, P0, has been cloned and localized to the same chromosomal region. P0 is a 28 kDa glycoprotein involved in the compaction of the multilamellar myelin sheet and accounts for more than half of the peripheral myelin protein content. We checked whether P0 is altered in CMT1B, and show here that a 3 basepair deletion in exon 2 of the P0 gene is present in all affected individuals of a CMT1B family. The mutation results in the deletion of serine 34 in the extracellular domain of P0, suggesting that alterations of P0 cause CMT1B.

N-glycosylation and deletion mutants of the human MDR1 P-glycoprotein

P-glycoproteins are heavily glycosylated plasma membrane proteins, which confer multidrug resistance by pumping a range of different drugs from the cell. To investigate the significance of the conserved N-glycosylation sites present in the putative first extracellular loop of P-glycoproteins, we mutated one, two, or all three of these sites present in the human MDR1 P-glycoprotein. We also deleted a stretch of 20 amino acids, containing two of the three N-glycosylation sites. The effects of these mutations were studied by transfection into drug-sensitive cells. In vincristine-resistant transfected clones selected for similar steady state levels of membrane-bound P-glycoprotein, the absence of N-glycosylation did not alter the level or pattern of (cross-)resistance. However, the absence of N-glycosylation sites drastically reduced the efficiency with which drug-resistant clones could be generated. These findings suggest that N-glycosylation contributes to proper routing or stability of P-glycoprotein but not to drug transport per se. The deletion mutants demonstrated a clearly decreased and altered drug resistance pattern, even with a high level of P-glycoprotein in the plasma membrane. This, and possibly the observed lack of glycosylation of the remaining intact glycosylation sequence, suggests a constrained P-glycoprotein structure. Our findings support the current model for P-glycoprotein structure.

Recognition and recall of visual area

When visual areas are recalled the ratio of two areas is compressed relative to both the actual and perceived values (e.g. Kemp, 1988). Experiment 1 replicated this effect with a simple two-region figure, and Expt 2 showed a significant increase in area compression to occur between 2 min and 1 week when subjects were asked to recognize the two-region figure from a set of nine figures with different area ratios. Area compression was also found in Expt 3 where a different figure was used. Experiment 4 found that varying the texture of the smaller region of a two-region figure had no significant effect on area compression, and in Expt 5 subjects choose a figure in which the area was expanded but the texture was unchanged over one in which the texture was expanded with the area. Experiment 6 showed that compression of remembered areas seen in a photograph did not depend on recalled distance. In conclusion, area compression appears to arise from a gradual transformation of remembered area that does not resemble a zooming process.