Protein phosphatase 6 activates NF-κB to confer sensitivity to MAPK pathway inhibitors in KRAS- and BRAF-mutant cancer cells

The Ras-mitogen-activated protein kinase (MAPK) pathway is a major target for cancer treatment. To better understand the genetic pathways that modulate cancer cell sensitivity to MAPK pathway inhibitors, we performed a CRISPR knockout screen with MAPK pathway inhibitors on a colorectal cancer (CRC) cell line carrying mutant KRAS. Genetic deletion of the catalytic subunit of protein phosphatase 6 (PP6), encoded by PPP6C, rendered KRAS- and BRAF-mutant CRC and BRAF-mutant melanoma cells more resistant to these inhibitors. In the absence of MAPK pathway inhibition, PPP6C deletion in CRC cells decreased cell proliferation in two-dimensional (2D) adherent cultures but accelerated the growth of tumor spheroids in 3D culture and tumor xenografts in vivo. PPP6C deletion enhanced the activation of nuclear factor κB (NF-κB) signaling in CRC and melanoma cells and circumvented the cell cycle arrest and decreased cyclin D1 abundance induced by MAPK pathway blockade in CRC cells. Inhibiting NF-κB activity by genetic and pharmacological means restored the sensitivity of PPP6C-deficient cells to MAPK pathway inhibition in CRC and melanoma cells in vitro and in CRC cells in vivo. Furthermore, a R264 point mutation in PPP6C conferred loss of function in CRC cells, phenocopying the enhanced NF-κB activation and resistance to MAPK pathway inhibition observed for PPP6C deletion. These findings demonstrate that PP6 constrains the growth of KRAS- and BRAF-mutant cancer cells, implicates the PP6-NF-κB axis as a modulator of MAPK pathway output, and presents a rationale for cotargeting the NF-κB pathway in PPP6C-mutant cancer cells.

SF3B1 hotspot mutations confer sensitivity to PARP inhibition by eliciting a defective replication stress response

SF3B1 hotspot mutations are associated with a poor prognosis in several tumor types and lead to global disruption of canonical splicing. Through synthetic lethal drug screens, we identify that SF3B1 mutant (SF3B1MUT) cells are selectively sensitive to poly (ADP-ribose) polymerase inhibitors (PARPi), independent of hotspot mutation and tumor site. SF3B1MUT cells display a defective response to PARPi-induced replication stress that occurs via downregulation of the cyclin-dependent kinase 2 interacting protein (CINP), leading to increased replication fork origin firing and loss of phosphorylated CHK1 (pCHK1; S317) induction. This results in subsequent failure to resolve DNA replication intermediates and G2/M cell cycle arrest. These defects are rescued through CINP overexpression, or further targeted by a combination of ataxia-telangiectasia mutated and PARP inhibition. In vivo, PARPi produce profound antitumor effects in multiple SF3B1MUT cancer models and eliminate distant metastases. These data provide the rationale for testing the clinical efficacy of PARPi in a biomarker-driven, homologous recombination proficient, patient population.

Abstract P6-10-05: Mutations in the RNA Splicing Factor SF3B1 drive endocrine therapy resistance and confer a targetable replication stress response defect through PARP inhibition

Background: Heterozygous hotspot mutations in the RNA splicing factor SF3B1, occur in 3% of unselected breast cancers and are associated with oestrogen receptor (ER+) breast cancer (BC) where they are enriched in metastatic disease and are associated with a poor clinical outcome. SF3B1 mutations drive distinct signatures of alternative splicing through cryptic 3’ splice site selection leading to global transcriptomic and proteomic changes. The functional consequences of the mis-splicing events and resultant genetic vulnerabilities are poorly understood and precision medicine approaches that exploit these characteristics are not clinically available (Table 1).

Methods: To understand the role of SF3B1 mutations in ER+ BC, we generated a series of SF3B1 mutant (SF3B1MUT) isogenic cell lines which were characterised using RNA-sequencing and high content mass-spectrometry proteomic profiling. SF3B1 interactome analysis was also performed using immunoprecipitation of SF3B1 followed by mass-spectrometry. The molecular consequences of aberrant splicing were investigated using a targeted screening approach of 280 genes predicted to be alternatively spliced in SF3B1MUT BC, while high-throughput drug screens were used to identify novel therapeutic options for patients with SF3B1MUT breast cancer using isogenic cells. Hits were validated in vitro and in vivo using cell line and patient derived xenografts.

Results: Transcriptomic and proteomic profiling of SF3B1MUT cells identified global alternative 3’ splice site selection and subsequent proteomic changes induced by the mutations. Investigation of the SF3B1K700E interactome identified an enrichment of SF3B1K700E binding with ER, aberrant splicing of ER target genes, global rewiring of ER chromatin binding and resistance to endocrine therapy. Silencing of the aberrantly spliced candidate genes PPIH, TRIM37, HIGD1A, BRD9, and PHKG2 significantly enhanced the growth of the SF3B1 mutant cells, suggestive of a dose dependent tumour suppressive effect.

Through synthetic-lethal drug screens we found that SF3B1MUT cells are selectively sensitive to PARP inhibitors. SF3B1MUT cells display a defective response to PARPi induced replication stress. Mechanistically, this occurs via defective ATR signalling in SF3B1MUT cells, which upon PARPi exposure leads to increased replication origin firing and loss of pChk1 (S317) induction. The resultant replication stress leads to failure to resolve DNA replication intermediates via the endonuclease MUS81 and cell cycle stalling at the G2/M checkpoint. These defects can be further targeted by ATM, CDK7 or FACT inhibition, when used in combination with PARPi treatment. This SF3B1MUT selective PARPi sensitivity is preserved across multiple cell lines and patient derived tumour models. In vivo, PARPi produce profound anti-tumour effects in multiple SF3B1MUT cancer models and eliminate distant metastases.

Conclusions: Our integrative analysis reveals mechanistic insight into the role of SF3B1 mutations in endocrine therapy response in ER+ breast cancers, where altered SF3B1 induces ER-transcriptional re-programming. We further identified a robust synthetic-lethal relationship of mutant SF3B1 with PARP inhibition that is caused by a defective response to PARPi induced replication stress. Furthermore, we identified several potential selective combination strategies together with PARPi that are selective for SF3B1MUT cells. Together, these data provide the pre-clinical and mechanistic rationale for assessing already-approved PARPi in a biomarker-defined subset of advanced ER+ BC.

Table 1. Identified potential therapies for SF3B1 mutant cancers from this study and the literature

Citation Format: Phil Bland, Harry Saville, Abigail Read, Patty Wai, Gareth Muirhead, Lucinda Curnow, Jadwiga Nieminuszczy, Nivedita Ravindran, Marie John, Somaieh Hedayat, Holly Barker, James Wright, Lu Yu, Ioanna Mavrommati, Barrie Peck, Mark Allen, Patrycja Gazinska, Helen Pemberton, Aditi Gulati, Sarah Nash, Farzana Noor, Naomi Guppy, Ioannis Roxanis, Samantha Barlow, Helen Kalirai, Sarah Coupland, Ronan Broderick, Samar Alsafadi, Alexandre Houy, Marc-Henri Stern, Stephen Pettit, Jyoti Choudhary, Syed Haider, Wojciech Niedzwiedz, Christopher Lord, Rachael Natrajan. Mutations in the RNA Splicing Factor SF3B1 drive endocrine therapy resistance and confer a targetable replication stress response defect through PARP inhibition. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-10-05.

Hotspot SF3B1 mutations induce metabolic reprogramming and vulnerability to serine deprivation

Cancer-associated mutations in the spliceosome gene SF3B1 create a neomorphic protein that produces aberrant mRNA splicing in hundreds of genes, but the ensuing biologic and therapeutic consequences of this missplicing are not well understood. Here we have provided evidence that aberrant splicing by mutant SF3B1 altered the transcriptome, proteome, and metabolome of human cells, leading to missplicing-associated downregulation of metabolic genes, decreased mitochondrial respiration, and suppression of the serine synthesis pathway. We also found that mutant SF3B1 induces vulnerability to deprivation of the nonessential amino acid serine, which was mediated by missplicing-associated downregulation of the serine synthesis pathway enzyme PHGDH. This vulnerability was manifest both in vitro and in vivo, as dietary restriction of serine and glycine in mice was able to inhibit the growth of SF3B1MUT xenografts. These findings describe a role for SF3B1 mutations in altered energy metabolism, and they offer a new therapeutic strategy against SF3B1MUT cancers.

Splicing dysregulation as a driver of breast cancer

Breast cancer is known to be a heterogeneous disease driven by a large repertoire of molecular abnormalities, which contribute to its diverse clinical behaviour. Despite the success of targeted therapy approaches for breast cancer patient management, there is still a lack of the molecular understanding of aggressive forms of the disease and clinical management of these patients remains difficult. The advent of high-throughput sequencing technologies has paved the way for a more complete understanding of the molecular make-up of the breast cancer genome. As such, it is becoming apparent that disruption of canonical splicing within breast cancer governs its clinical progression. In this review, we discuss the role of dysregulation of spliceosomal component genes and associated factors in the progression of breast cancer, their role in therapy resistance and the use of quantitative isoform expression as potential prognostic and predictive biomarkers with a particular focus on oestrogen receptor-positive breast cancer.

Rapid assessment of potential for development of large dams and irrigation across continental areas: application to northern Australia

Water scarcity in southern Australia and an imperative to develop regional economies have combined to renew focus on the potential for irrigated agricultural development in Australia’s largely undeveloped and sparsely populated north. More than 2 billion potential dam sites across northern Australia (an area of ~3 million km2) were assessed in a consistent and objective manner, using the DamSite model, in the largest comprehensive assessment of large dams undertaken globally. Simultaneous consideration was given to large dams and their proximity to land physically suited to the development of irrigated cropping and horticulture. We did not consider regulatory and land-ownership limitations on irrigation and dam development or social, environmental and economic considerations. Although these factors do and will constrain water and agricultural development in northern Australia, each requires a site-specific analysis, and these factors can potentially change with time. Physical resources (soil, surface water, and topography suitable for large, in-stream dams) sufficient to support ~1.84 Mha of irrigated agriculture exist in northern Australia. This would require use of the entire yield from eight existing dams (including the Burdekin Falls and Ord River dams) and the construction of 117 new dams. A more financially attractive option could involve using water from 85 large dams (eight existing and 77 new dams) and a large number of reregulating structures (e.g. weirs) to irrigate 1.34 Mha of land suitable for irrigated agriculture. If realised, this would result in a ~50% increase in Australia’s area under irrigation. Approximately 50% of the potential 1.34 Mha of irrigated land in northern Australia (~670 000 ha) could be irrigated with ~20 of the more promising large dams, highlighting the declining marginal returns to dam construction and the benefits of strategic land and water resource planning. In reality, a range of regulatory, political and socio-economic factors will considerably constrain the upper physical limit to dam and irrigation development stated in this paper. They may also inevitably result in major developments occurring over longer timeframes than dam and irrigation developments of comparable scale in southern Australia during the 20th Century. Alternative sources of water (e.g. groundwater, wetlands, waterholes) and water storage (e.g. gully dams, ringtanks, managed aquifer recharge) are physically capable of supplying smaller volumes of water than large dams, although each may have important roles to play in maximising the cost-effectiveness of water supply in northern Australia.

Flexible CRISPR library construction using parallel oligonucleotide retrieval

CRISPR/Cas9-based gene knockout libraries have emerged as a powerful tool for functional screens. We present here a set of pre-designed human and mouse sgRNA sequences that are optimized for both high on-target potency and low off-target effect. To maximize the chance of target gene inactivation, sgRNAs were curated to target both 5΄ constitutive exons and exons that encode conserved protein domains. We describe here a robust and cost-effective method to construct multiple small sized CRISPR library from a single oligo pool generated by array synthesis using parallel oligonucleotide retrieval. Together, these resources provide a convenient means for individual labs to generate customized CRISPR libraries of variable size and coverage depth for functional genomics application.

Abstract 1042: CLIC4 is incorporated into extracellular vesicles of murine breast cancer cells and may influence metastatic burden

Chloride intracellular channel 4 (CLIC4) is an evolutionarily conserved, 29kD, dimorphic protein that contributes to TGF-β signaling by preventing the de-phosphorylation of phospho-SMAD2/3 upon nuclear translocation. In several cancer types, CLIC4 is excluded from the nucleus and downregulated in the cytoplasm of the tumor cells as the tumor progresses, suggesting that CLIC4 acts as tumor suppressor. In a parallel sequence, CLIC4 becomes upregulated in the stromal compartment, where it enhances tumor growth and invasion. Recent reports have suggested that CLIC4 is detectable in the serum of cancer patients and incorporated into extracellular vesicles, and has potential as a biomarker. We hope to gain a better understanding of the role that CLIC4 plays in the tumor stromal and epithelial compartments as well as their respective release of extracellular vesicles. Using in-vitro and in-vivo assays, we have conducted experiments using the FVB mouse MMTV-c-MYC 6DT1 breast cancer model. By CRISPR/ Cas9 system, CLIC4 was deleted from wild type 6DT1 cells. Following clonal selection, the loss of the CLIC4 protein at both the cellular and released vesicle level was validated. Both functional assays on CLIC4 deleted clones and evaluation of their extra-cellular vesicles were undertaken in order to further understand their tumorigenic and metastatic capabilities. In-vitro, CLIC4 was not necessary for vesicle biogenesis and its deletion did not have a significant effect on cellular proliferation. In vivo, selected clones were orthotopically injected into the 4th mammary fat pad of wild type FVB mice. Compared to wild type 6DT1 clones, CLIC4 deleted clones formed primary tumors that had greater mass but a fewer number of lung metastasis. Future studies are designed to isolate vesicles circulating in tumor bearing hosts to determine their stromal or epithelial origin and to provide a better understanding of the role that CLIC4 may play in tumor growth, creating a metastatic niche and as a potential serological biomarker.

Citation Format: Alayna B. Craig-Lucas, Vanesa C. Sanchez, Abigail Read, Ji Lou, Anjali Shukla, Stuart H. Yuspa. CLIC4 is incorporated into extracellular vesicles of murine breast cancer cells and may influence metastatic burden [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1042. doi:10.1158/1538-7445.AM2017-1042

One-step immortalization of primary human airway epithelial cells capable of oncogenic transformation

BACKGROUND

The ability to transform normal human cells into cancer cells with the introduction of defined genetic alterations is a valuable method for understanding the mechanisms of oncogenesis. Easy establishment of immortalized but non-transformed human cells from various tissues would facilitate these genetic analyses.

RESULTS

We report here a simple, one-step immortalization method that involves retroviral vector mediated co-expression of the human telomerase protein and a shRNA targeting the CDKN2A gene locus. We demonstrate that this method could successfully immortalize human small airway epithelial cells while maintaining their chromosomal stability. We further showed that these cells retain p53 activity and can be transformed by the KRAS oncogene.

CONCLUSIONS

Our method simplifies the immortalization process and is broadly applicable for establishing immortalized epithelial cell lines from primary human tissues for cancer research.

Dental admissions in children under two years--a total-population investigation

BACKGROUND

There is a lack of literature describing dental admissions in children particularly very young children. This paper describes dental and oral cavity admissions and associated factors in children under two years of age using total-population databases.

METHODS

The data used for this study were extracted from population-based databases which are linkable with midwives' data collected on all births in Western Australia. Children born from 1980 to 1998 inclusive (n = 459,831) were followed until two years of age including data on deaths, hospital admissions, birth defects and intellectual disability. Dental admissions (by ICD-9 category) and associated factors were investigated.

RESULTS

There were 1513 dental admissions occurring in 1459 of the children up to the age of two years. Children were most frequently admitted under ICD-9 category 521, which includes a hospital admission for dental caries (39% of all oral cavity admissions), followed by ICD-9 category 528 (29%), which includes diseases of the oral soft tissues. Univariate analysis indicated that those with intellectual disability (OR 2.10, 95%CI 1.40-3.16), birth defect (1.74, 1.45-2.09), residing in a region without fluoridated water (2.15, 1.72-2.69) being male (1.14, 1.03-1.26), those from rural areas (2.29, 2.07-2.54) and Indigenous children (4.45, 3.91-5.05) were significantly more likely to have had a dental admission.

CONCLUSION

Using total-population data allowed us to describe the admissions in children under two years and associated factors while able to identify children with intellectual disability or birth defects.

Reduced appetite and body mass index with delayed puberty in a mother and son: association with a rare novel sequence variant in the leptin gene

INTRODUCTION

Leptin deficiency caused by mutations within the leptin gene (LEP) results in severe early onset obesity, hypogonadism, pubertal delay and immune system abnormalities. Constitutional delay in growth and puberty (CDGP) is a common condition seen in paediatric clinics, in which children present with delayed growth and puberty but usually also have a slim body habitus. We hypothesized that LEP variants may play a role in the phenotype seen in CDGP.

AIM

To screen a group of children with CDGP for pathogenic sequence variants in LEP.

PATIENTS AND METHODS

Denaturing HPLC was used to screen for LEP sequence variants in DNA samples from 78 children with CDGP (predominantly white males) and 112 control subjects. DNA fragments with a WAVE pattern deviant from wild type were directly sequenced. A STAT3 luciferase reporter assay in human embryonic kidney (HEK293) cells transiently transfected with the leptin receptor was used to test activity of mutant leptin.

RESULTS

One child with CDGP was identified to be heterozygous for a novel missense variant (c.68C>G), which results in a proline to arginine substitution (p.P23R). This sequence variant was not identified in any of the other control subjects, but was identified in his mother who shared a similar phenotype of slim body habitus, reduced appetite and pubertal delay (menarche aged 15 years). The leptin variant showed similar stability in serum compared with wild type and did not demonstrate increased activity in an in vitro reporter gene assay.

CONCLUSIONS

This is the first report of a sequence variant within the LEP gene associated with reduced body mass index rather than obesity. We hypothesize that this variant has increased bioactivity in vivo.

Development of a new quality fair access best value performance indicator (BVPI) for recycling services

Recycling schemes are being used worldwide to reduce the impact of municipal waste. Those using public funds are usually obliged to set performance indicators by which the standards of such schemes can be measured. In the UK, a set of statutory Best Value Performance Indicators (BVPI) must be reported annually, such as the Quality of Fair Access, which monitors the public's access to recycling facilities within 1000 m (known as BVPI 91). This work shows that BVPI 91, and performance indicators like it, quantify only very basic recycling services. A much more sensitive performance indicator is developed in this paper, labelled as the Maximum Practicable Recycling Rate Provision (MPRRP) achievable by a local authority. It indicates the percentage of local waste that could be reasonably recycled using the services provided, calculated on the basis of the average composition of the local waste, the local population coverage for collection of any materials, and nationally provided information stating how much of each material stream is generally suitable (practical) for recycling. Evidence for the usefulness of this new quantity is presented. Although this paper refers a particular performance indicator in the UK, its findings are applicable to all urban areas worldwide needing to monitor recycling service. Furthermore, the MPRRP could be used for planning purposes, and for determining the level of performance of an existing service, by comparing its predicted recycling rate to that actually obtained. Further work is now being carried out on this.

Genital abnormalities mimicking congenital adrenal hyperplasia in premature infants

Unusual genital appearances in premature infants can be easily mistaken for true ambiguous genitalia, with alarming consequences. The results of blood and urine tests carried out for premature infants can be misleading due to persistence of the foetal zone of the adrenal cortex. More importantly, misdiagnosis is devastating for the parents and adds significantly to their distress. Here, we describe two patients with transient genital abnormalities and abnormal biochemical tests.

Thyrotoxic, hypokalaemic periodic paralysis in Australasian men

Abstract The present study describes the clinical and laboratory features of 11 patients with thyrotoxic, hypokalaemic periodic paralysis, presenting to five Melbourne teaching hospitals between 1991 and 2000. All 11 patients were Asian or Polynesian men aged 18-41 years, and most had experienced previous episodes of acute, unexplained paralysis. All cases resolved without significant morbidity. Thyrotoxic, hypokalaemic periodic paralysis is a potentially life-threatening and terrifying condition, which is often under-recognized and will present with increasing frequency in the community. The diagnosis should be considered in any Asian-Australian male presenting with sudden onset paralysis.

Molecular genetic analysis of the NF2 gene in young patients with unilateral vestibular schwannomas

Neurofibromatosis type 2 (NF2) must be suspected in patients presenting with a unilateral vestibular schwannoma at a young age who are therefore at theoretical risk of developing bilateral disease. We identified 45 patients aged 30 years or less at the onset of symptoms of a unilateral vestibular schwannoma. Molecular genetic analysis of the NF2 gene was completed on peripheral blood samples in all 45 and on 28 tumour samples. No pathogenic NF2 mutations were identified in any of the blood samples. NF2 point mutations were identified in 21/28 (75%) tumour samples and loss of heterozygosity (LOH) in 21/28 (75%) tumour samples. Both mutational hits were identified in 18/28 (65%) tumour samples. In one multilobular tumour, one (presumably first hit) mutation was confirmed which was common to different foci of the tumour, while the second mutational event differed between foci. The molecular findings in this patient were consistent with somatic mosaicism for NF2 and the clinical diagnosis was confirmed with the presence of two meningiomas on a follow up MRI scan. A further patient developed a contralateral vestibular schwannoma on a follow up MRI scan in whom neither of the truncating mutations in the vestibular schwannoma were present in blood. It is important when counselling patients with unilateral vestibular schwannomas to identify (1) those at risk of bilateral disease, (2) those at risk of developing other tumours, and (3) other family members at risk of developing NF2. Comparing tumour and blood DNA cannot exclude mosaicism in the index case and cannot, therefore, be used to predict those at risk of developing further tumours. However, identification of both mutations or one mutation plus LOH in the tumour and exclusion of those mutations in the blood samples of the sibs or offspring of the affected case may be sufficient to render further screening unnecessary in these relatives.

The transcription factor onecut-2 controls the microphthalmia-associated transcription factor gene

Microphthalmia-associated transcription factor (MITF) is essential for melanocyte differentiation. MITF mutations are associated with some cases of Waardenburg syndrome (WS) type 2. WS is a dominantly inherited disease characterized by auditory-pigmentary defects that result from the absence of melanocytes. The lack of mutation in MITF coding sequences in some WS2 patients suggests that unidentified factors controlling MITF expression might be involved. We show here that the cut-homeodomain transcription factor Onecut-2 (OC-2) is expressed in melanocytes and binds to the MITF gene promoter. Overexpression of OC-2 in transfected cells stimulates MITF promoter activity. Mutations that prevent OC-2 binding decrease MITF promoter activity by 75%. Based on these results, we searched in 56 WS2 patients for mutations in the OC2 gene or in OC-2 binding sites in the MITF promoter, but none was found. These results show that OC-2 stimulates MITF expression and that OC2 is a candidate gene, but not a common cause, of WS.

Inhibitory effects during object name retrieval: the effect of interval between prime and target on picture naming responses

Three picture naming experiments are reported which examine the relationship between the apparent inhibition of a response on one trial, and naming latency on the subsequent trial. The design of each experiment involves the presentation of prime and target pairs, either presented in succession (Lag 1 condition), or separated by two intervening unrelated trials (Lag 3 condition). A control condition is also included. In Experiment 1, a speeded picture naming task is used, and naming errors are analysed. Target pictures are misnamed at above chance rates with the name of the semantically related prime picture in the Lag 3 condition. In contrast, these prime-related errors do not occur in the Lag 1 condition, suggesting a brief inhibitory effect. If primes are briefly inhibited, then target naming latencies immediately following a related prime should be quicker than target latencies in the Lag 3 condition. Experiment 2 confirms this pattern of results, using exactly the same stimuli and design, but standard naming instructions. Experiment 3 examines whether the inferred inhibition is the result of a self-inhibitory mechanism, using a repetition priming paradigm. If Lag 1 prime representations are self-inhibited, then facilitatory effects from prime/target repetition should be stronger in the Lag 3 condition, than in the Lag 1 condition. The data from Expt 3 were not consistent with this prediction. Taken together, the results of the three experiments suggest that a brief inhibitory effect occurs after retrieval of an object name, and that the inhibition may be accomplished by mechanisms other than self-inhibition.

Plasmodium chabaudi: effect of antimalarial drugs on gametocytogenesis

The proportion of asexual blood-stage malaria parasites that develop into transmission stages (gametocytes) can increase in response to stress. We investigated whether stress imposed by a variety of antimalarial drugs administered before or during infection increased gametocyte production (gametocytogenesis) in vivo in the rodent malaria parasite, Plasmodium chabaudi. All methods of drug treatment greatly reduced the numbers of asexual parasites produced during an infection but resulted in either no reduction in numbers of gametocytes or a smaller reduction than that experienced by asexuals. We used a simple model to estimate temporal variation in gametocyte production. Temporal patterns of gametocytogenesis did not greatly differ between untreated and prophylaxis infections, with rates of gametocytogenesis always increasing as the infection progressed. In contrast, administration of drugs 5 days after infection stimulated increased rates of gametocytogenesis early in the infection, resulting in earlier peak gametocyte densities relative to untreated infections. Given the correlation between gametocyte densities and infectivity to mosquito vectors, and the high frequency of subcurative drug therapy and prophylaxis in human populations, these data suggest that antimalarial drugs may frequently have only a small effect on reducing malaria transmission and may help to explain the rapid spread of drug-resistant geno-types.

X-inactivation and marker studies in three families with incontinentia pigmenti: implications for counselling and gene localisation

Familial incontinentia pigmenti (IP) is an X-linked dominant disorder with an extremely variable clinical presentation. Ambiguous diagnosis can complicate genetic counselling and attempts to refine the gene location in Xq28. Marked skewing of X-inactivation patterns is a hallmark of IP and provides a means for investigating uncertain cases. We have conducted X-inactivation studies in three families where Xq28 marker studies were at odds with the original clinical assessment. The results indicate that no recombination between the disease locus and Xq28 loci has occurred and suggest that mosaicism is responsible for the discrepancy in one family.

Linkage analysis in 16 families with incontinentia pigmenti

A locus for the X-linked dominant genodermatosis incontinentia pigmenti (IP) has been linked to markers in Xq28. Here we report high lod scores for markers spanning the interval DXS52-DXYS154 using 16 families, providing further evidence for a single major X-linked IP locus.

Reducing naltrexone-resistant hyperphagia using laser acupuncture to increase endogenous opiates

A 28-year-old woman with acquired brain damage suffered subsequent profound mental disability and an intense hyperphagic syndrome complete with life-threatening pica. She was the single subject of two consecutive experiments. In the first, Naltrexone, an orally administered opiate blocker, was given to reduce hyperphagia and distress, but was associated with even greater urgency when eating meals and a manifest increase in distress. While distress reduced to premedication levels on withdrawal of treatment, urgency of eating did not reduce so quickly. In the second experiment a laser acupuncture procedure was used at 2.5 Hz and 10 Hz for 10 days each with an intervening 10-day placebo condition to increase the availability of the subject's endogenous opiates, and thus hopefully produce opposite effects to the first experiment and effect a positive treatment. The 10 Hz condition produced a significant but transient reduction in pica measured by attempts at pica on a supervised walk shortly after each treatment. The subject was also easier to manage on walks, and appeared happier. Further studies using physical exercise or acupressure to achieve similar or better results are discussed.

Helminth immunogenetics: Why bother?

The importance of host genotype as a determinant of protective responses against helminth infection is well established. In contrast, there have been relatively few investigations of the role of helminth genotype, despite the importance accorded to the genetics of other disease-causing organisms. Here, Andrew Read and Mark Viney discuss the reasons for this oversight. They argue that it is not for any compelling empirical reason: there is at least as much evidence that worm genetics affects host protective responsiveness as there is that it does not.

Allelic imbalance on chromosome 3p in oral dysplastic lesions: an early event in oral carcinogenesis

We have demonstrated previously a loss of constitutional heterozygosity on the short arm of chromosome 3 in approximately 50% of oral squamous cell carcinomas. In the present study, we have investigated 30 oral dysplastic lesions (DLs), presenting clinically as either erythroplakias or leukoplakias with histopathological features of either severe epithelial dysplasia or carcinoma in situ, for LOH on chromosome 3p using 15 microsatellite markers. Thirteen of the 30 LDs (approximately 43%) showed allelic imbalance at one or more loci. The pattern of loss in these lesions defined three noncontiguous regions of interstitial deletions that overlap with those defined for oral squamous cell carcinomas. These data indicate that the alteration of tumor suppressor genes on chromosome 3p is probably an early event in oral carcinogenesis. Additionally, 7 of the 30 DLs showed microsatellite instability. However, the frequency of loci showing microsatellite instability per lesion was low.

Hearing loss and pigmentary disturbances in Waardenburg syndrome with reference to WS type II

Thirty families in which there were 149 individuals affected by the Waardenburg syndrome (WS) were investigated for penetrance of hearing loss and pigmentary abnormalities. Twenty two families contained 89 individuals affected by WS Type II and eight families with 60 individuals affected by Type I. A bilateral symmetrical sensorineural hearing loss was found to be the most common type of hearing loss. The most frequent degree of hearing loss category was a hearing loss of > 100dB HL with no difference between syndrome types. Although there was no significant difference in the frequency of pigmentation disorders between Type I and II, considering these abnormalities as a whole, heterochromia irides was more common in Type II than Type I and other pigmentation disorders were more frequent in Type I: 62 per cent of Type I patients had more than one pigmentary defect, but only 28 per cent of Type II. Pigmentary disturbances were not significantly more frequent in the hearing impaired group than in the normally hearing group in either Type I or II when taking into account the occurrence of only one pigmentation disorder. There was a significantly higher proportion of pigmentary defects in the hearing impaired group with Type I when only those having more than one pigmentary abnormality were compared: 93.3 per cent of Type I patients and 88.5 per cent of Type II patients with a profound hearing loss had pigmentary defects. The frequency of pigmentation disorders was not greater when the hearing loss was more severe in either type. Penetrance for hearing loss and pigmentary abnormalities showed marked intrafamilial and interfamilial variation.

Fine structure mapping of the human X-linked hypophosphatemic rickets gene locus

X-linked hypophosphatemic rickets (HYP) is an X-linked dominant disorder characterized by decreased renal tubular phosphate reabsorption and consequent hypophosphatemia. Renal cross-transplantation studies in Hyp mice indicate that the disorder is secondary to the elaboration of an as yet unidentified humoral factor. A full understanding of the pathophysiology of the disease and the nature of this factor will be facilitated by identification of the HYP gene. Efforts to isolate the HYP gene have been deterred by limited precision in the map of the Xp22.1 region and the consequent distance between DXS365 and DXS274, the previously discovered flanking markers for the HYP gene. To map the HYP region precisely, HYP family resources from two groups of investigators were combined, and several newly available microsatellite repeat probes were tested for linkage to HYP. Our data indicate that DXS365, DXS3424, DXS443, DXS1052, DXS274, and DXS1683 are tightly linked to the HYP gene and suggest a locus order of: Xtel-DXS315-(GLR/DXS43)-DXS257-(DXS443+ ++-DXS3424)-DXS365-HYP-DXS1683-DXS1052-DXS 274-(DXS41/DXS92)-DXS451-Xcen. The HYP gene is located in the 350- to 650-kilobase region between DXS365 and DXS1683. These results will provide a basis for the isolation of candidate genes from the region.

Molecular basis of splotch and Waardenburg Pax-3 mutations

Pax genes control certain aspects of development, as mutations result in (semi)dominant defects apparent during embryogenesis. Pax-3 has been associated with the mouse mutant splotch (Sp) and the human Waardenburg syndrome type 1 (WS1). We have examined the molecular basis of splotch and WS1 by studying the effect of mutations on DNA binding, using a defined target sequence. Pax-3 contains two different types of functional DNA-binding domains, a paired domain and a homeodomain. Mutational analysis of Pax-3 reveals different modes of DNA binding depending on the presence of these domains. A segment of Pax-3 located between the two DNA-binding domains, including a conserved octapeptide, participates in protein homodimerization. Pax-3 mutations found in splotch alleles and WS1 individuals change DNA binding and, in the case of a protein product of the Sp allele, dimerization. These findings were taken as a basis to define the molecular nature of the mutants.

Refining the genetic map for the region flanking the X-linked hypophosphataemic rickets locus (Xp22.1-22.2)

We have screened fourteen kindreds with X-linked hypophosphataemic rickets with four microsatellite markers, viz AFM163yh2, DXS999 (AFM234yf12), DXS443 and DXS365, in order to refine the genetic map flanking the gene, and to define a close flanking interval for the construction of a yeast artificial chromosome (YAC) and cosmid contig. The genetic data were enhanced after the isolation of a large 1.2-megabase YAC derived from AFM163yh2, in which marker DXS274 was present but not DXS365 or DXS443. Against HYP, DXS365, AFM163yh2 and DXS443 showed no recombinants (Zmax = 18.1, Zmax = 9.9, and Zmax = 16.0 respectively). DXS999 gave Zmax = 9.6 at 4% recombination and lies distal to HYP but proximal to DXS197 and DXS43. The disease gene and markers AFM163yh2 and DXS365 are flanked by DXS443 and DXS274. Combining the genetic and physical data, we are able to propose the following gene marker order: Xptel-DXS43-DXS197-DXS999-DXS443-[(DXS3 65-AFM163yh2), HYP]-DXS274-DXS41-Xcen.

Immunogenicity of two recombinant hepatitis B vaccines in older individuals

PURPOSE

Currently available hepatitis B vaccines are recombinant, yeast-derived preparations given in 10-micrograms or 20-micrograms doses. The optimum dose remains controversial. We sought to assess the relative immunogenicity of two hepatitis B vaccines, given in different doses, in older individuals.

PATIENTS AND METHODS

In a multicenter, double-blind, randomized clinical trial, a total of 460 healthy subjects between 39 and 70 years of age were screened and immunized with either Engerix-B 20 micrograms or Recombivax HB 10 micrograms in standard, intramuscular, 3-dose regimens. Of these, 397 subjects were eligible to continue vaccination. Immunogenicity was measured by determination of antibody to hepatitis B surface antigen (anti-HBs). Seroconversion and seroprotection rates, and geometric mean titers of anti-HBs were calculated at 1, 3, 6, and 8 months after the initial dose of vaccine.

RESULTS

Seroprotection rates for subjects receiving the 20-micrograms dose of vaccine were slightly, but not significantly, greater than for subjects receiving the 10-micrograms dose, at each time point. However, at 3 months, males receiving the higher dose had significantly higher seroprotection rates than males receiving the lower dose: 63% versus 37% (p < 0.001). At 8 months, geometric mean titers for the group receiving Engerix-B 20 micrograms were significantly greater than that for the group receiving Recombivax HB 10 micrograms: 840 mIU/mL versus 340 mIU/mL (p = 0.001).

CONCLUSIONS

Immunization with the 20-micrograms dose of recombinant hepatitis B virus vaccine appeared to result in more rapid development of seroprotective anti-HBs titers in older men and in higher titers of anti-HBs at the completion of vaccination when compared to the 10-micrograms dose. The latter data suggest that the 20-micrograms dose may result in a longer duration of seroprotective anti-HBs titers.

True telomeric translocation in a baby with the Prader-Willi phenotype

We report on a baby with a nonreciprocal de novo unbalanced translocation between chromosomes 12 and 15. Her karyotype was 45,XX, -12, -15, +der(12)t(12;15)(pter-->qter::q13-->qter). The paternal origin of the 15q11-13 region was shown by DNA marker studies and, consistent with this, the baby had the Prader-Willi (PWS) phenotype. The breakpoint on 12q was distal to D12S11 (lambda MS43) which maps to 12q24.3-qter. Fluorescent in situ hybridization using the oligonucleotides (TTAGGG)7 and (AATCCC)7 showed that the 12q telomere was still present within the translocated chromosome. Thus, the translocation was within or onto the end of the telomere of 12q. This unusual translocation is further evidence of an unexplained instability of the 15q11-13 region.

Percutaneous endoscopic gastrostomy: the Heidelberg Repatriation Hospital experience

Percutaneous endoscopic gastrostomy (PEG) was performed on 32 patients (mean age 75 years) who were dysphagic but enteral alimentation was possible. Seventeen patients were recovering from a stroke; the interval between the onset of stroke and PEG averaged 44 days. The procedure was successful and well tolerated by 16 of these 17 patients. Ten patients (31%) still had a functioning PEG, a median of 30 weeks after placement. Seven patients whose swallowing recovered had their tubes removed an average of 3 months after their insertion. Fifteen patients (47%) subsequently died from their underlying disease, a mean of 126 days following PEG. There were no deaths directly related to catheter placement. Percutaneous endoscopic gastrostomy is a useful alternative to surgical gastrostomy in elderly patients with long-term oral feeding problems.