Extent of Extraskeletal Manifestations of Fibrous Dysplasia/McCune-Albright Syndrome in Patients with Mazabraud's Syndrome.

Mazabraud's syndrome (MZB) is a rare condition in which fibrous dysplasia of bone/the McCune-Albright syndrome (FD/MAS) co-exists with intramuscular myxomas. Both FD and the myxomas harbor the GNAS-mutation. Recent studies have shown that extraskeletal, GNAS-related features are associated with a more severe phenotype of FD/MAS. However, patients with MZB are often only seen by orthopedic surgeons. We therefore evaluated MZB patients seen in tertiary referral centers from the Netherlands (LUMC), USA (National Institutes of Health) and France (INSERM UMR 1033 (Lyos), Hôpital Edouard Herriot). All FD/MAS patients known in these centers with an additional diagnosis of a myxoma were included. Demographic information and data on disease extent and extraskeletal manifestations of FD/MAS such as precocious puberty (PP) or café-au-lait patches (CAL) were retrieved from patient's medical records. Thirty MZB patients were included: 20 women (67%) and 10 men (33%). Patients received a diagnosis of MZB (median 42 years, range 16-19) significantly later than the diagnosis of FD/MAS (median 30 years, range 0-60), p < 0.01. Twenty-six patients were diagnosed with polyostotic disease (87%). In 97% the myxoma was located near the skeletal FD lesion. The combination of MZB and MAS was made in 13 patients in whom PP (n = 7), CAL (n = 7), GH-excess (n = 3) and hyperthyroidism (n = 3) were present. Other extraskeletal features were (multinodular) goiter (n = 2) and thyroid cysts (n = 1). Furthermore, in this cohort of patients with MZB several (pre-)malignant tumors were observed; ductal carcinoma in situ of the breast in 3 patients (10%), breast cancer in 1 patient (3.3%), intra pancreatic mucinous neoplasms in 3 patients (10%) and liver adenomas in 2 patients (6.6%). A total of 47% of patients with MZB had an additional extraskeletal feature such as an endocrinopathy. In MZB, 87% of patients suffer from polyostotic FD, 43% of patients have extraskeletal GNAS-features such as an hyperfunctioning endocrinopathy and 30% (pre-)malignant tumors. We therefore advocate that MZB patients should undergo a complete screening and long-term follow-up for extent of bone disease, but also extraskeletal GNAS features of FD/MAS.

Denosumab for craniofacial fibrous dysplasia: duration of efficacy and post-treatment effects.

Denosumab has been advocated as a potential treatment for the rare skeletal disorder fibrous dysplasia (FD); however, there is limited data to support safety and efficacy, particularly after drug discontinuation. We report a case of successful treatment of aggressive craniofacial FD with denosumab, highlighting novel insights into the duration of efficacy, surrogate treatment markers, and discontinuation effects. A 13-year-old girl presented with persistent pain and expansion of a maxillary FD lesion, which was not responsive to repeated surgical procedures or bisphosphonates. Pre-treatment biopsy showed high RANKL expression and localization with proliferation markers. Denosumab therapy was associated with improved pain, decreased bone turnover markers, and increased lesion density on computed tomography scan. During 3.5 years of treatment, the patient developed increased non-lesional bone density, and after denosumab discontinuation, she developed hypercalcemia managed with bisphosphonates. Pain relief and lesion stability continued for 2 years following treatment, and symptom recurrence coincided with increased bone turnover markers and decreased lesion density back to pre-treatment levels. This case highlights the importance of considering the duration of efficacy when treating patients with FD and other nonresectable skeletal neoplasms that require long-term management.

Resolved External Ophthalmoplegia and Hearing Loss in Wernicke's Encephalopathy With Thiamine Replacement.

BACKGROUND: Wernicke encephalopathy (WE) is classically described by a clinical triad consisting of confusion, ataxia, and ophthalmoplegia, but recent reports emphasize a history of malnutrition along with 2 elements of the WE triad (Caine's criteria) to enhance diagnostic sensitivity. The ophthalmoplegia, vestibular, and auditory expeditious improvement with intravenous thiamine usually confirms the diagnosis; serum levels generally provide additional diagnostic certainty. METHODS: Here, we discuss the case of a woman with a distant history of gastric sleeve, poor nutrition and protracted vomiting, who developed acute confusion, imbalance, near-total external ophthalmoplegia (EO), and hearing loss. The baseline thiamine level was 28 πmol/L (Normal: 70-180 πmol/L). We performed serial neurological, vestibular, and audiological examination to document over 5 days, the effect of intravenous (IV) thiamine, and again at 3 months with continued oral supplementation. We provide serial documentation with photographs and video recording of oculomotor abnormalities, audiometric testing, and a video of horizontal head impulse testing, and imaging findings. RESULTS: Over the course of 5 days of IV thiamine supplementation, we demonstrate our patient's resolution of near complete EO. We assessed vestibular paresis with horizontal head impulse testing, after complete resolution of the EO. The initially positive bilateral h-HIT showed decreased gain and overt corrective saccades, it clinically resolved by day 5, but video h-HIT testing demonstrated persistent decreased horizontal vestibulo-ocular reflex (VOR) gain and covert horizontal saccades, which persisted at the 3-month examination. By contrast, the vertical VOR gain was normal without corrective saccades. Bedside audiometry completed during the acute phase demonstrated severely restricted auditory speech comprehension, which normalized 3 months later. Severe truncal ataxia improved as well. CONCLUSIONS: This case is an example of how awareness of the variations in the clinical presentation of WE can be crucial in achieving an early diagnosis and obtaining better outcomes. A history of the poor nutritional status can be an important clue to aid in this early diagnosis.

TREatment of ATopic eczema (TREAT) Registry Taskforce: an international Delphi exercise to identify a core set of domains and domain items for national atopic eczema photo- and systemic therapy registries.

BACKGROUND: Evidence of immunomodulatory therapies to guide clinical management of atopic eczema (AE) is scarce, despite frequent and often off-label use. Patient registries provide valuable evidence for the effects of treatments under real-world conditions that can inform treatment guidelines, give the opportunity for health economic evaluation and the evaluation of quality of care, as well as pharmacogenetic and dynamic research, which cannot be adequately addressed in clinical trials. OBJECTIVES: The TREatment of ATopic eczema (TREAT) Registry Taskforce aims to seek international consensus on a core set of domains and items ('what to measure') for AE research registries, using a Delphi approach. METHODS: Participants from six stakeholder groups were included: doctors, nurses, nonclinical researchers, patients, industry and regulatory body representatives. The eDelphi comprised three sequential online rounds, requesting participants to rate the importance of each proposed domain item. Participants could add domain items to the proposed list in round 1. A final consensus meeting was held to ratify the core set. RESULTS: Participants (n = 479) from 36 countries accessed the eDelphi platform, of whom 86%, 79% and 74% completed rounds 1, 2 and 3, respectively. At the face-to-face consensus meeting attended by 42 participants the final core set was established containing 19 domains with 69 domain items (49 baseline and 20 follow-up items). CONCLUSIONS: This core set of domains and items to be captured by national AE systemic therapy registries will standardize data collection and thereby allow direct comparability across registries and facilitate data pooling between countries. Ultimately, it will provide greater insight into the effectiveness, safety and cost-effectiveness of photo- and systemic immunomodulatory therapies.

Bone marrow failure and extramedullary hematopoiesis in McCune-Albright syndrome.

In fibrous dysplasia/McCune-Albright syndrome (FD/MAS), bone and bone marrow are, to varying degrees, replaced by fibro-osseous tissue typically devoid of hematopoietic marrow. Despite the extensive marrow replacement in severely affected patients, bone marrow failure is not commonly associated with FD/MAS. We present a 14-year-old girl with FD/MAS, who developed pancytopenia and extramedullary hematopoiesis (EMH) with no identified cause, in the setting of iatrogenic thyrotoxicosis and hyperparathyroidism. Pancytopenia, requiring monthly blood transfusions, persisted despite multiple strategies to correct these endocrinopathies. Due to worsening painful splenomegaly, likely as a result of sequestration, splenectomy was performed. Following splenectomy, pancytopenia resolved and patient has since been transfusion-independent. We report the first detailed case of bone marrow failure and EMH in FD/MAS. The etiology of marrow failure is likely multifactorial and related to the loss of marrow reserve due to extensive polyostotic FD, exacerbated by iatrogenic thyrotoxicosis and hyperparathyroidism. Mini Abstract: A patient with fibrous dysplasia developed bone marrow failure and extramedullary hematopoiesis. The etiology likely involved loss of hematopoetic marrow space and uncontrolled endocrinopathies. Splenectomy was therapeutic.

Fibrous dysplasia of bone: craniofacial and dental implications.

Fibrous dysplasia (FD) is a rare bone disease caused by postzygotic somatic activating mutations in the GNAS gene, which lead to constitutive activation of adenylyl cyclase and elevated levels of cyclic AMP, which act on downstream signaling pathways and cause normal bone to be replaced with fibrous tissue and abnormal (woven) bone. The bone disease may occur in one bone (monostotic), multiple bones (polyostotic), or in combination with hyperfunctioning endocrinopathies and hyperpigmented skin lesions (in the setting of McCune-Albright Syndrome). FD is common in the craniofacial skeleton, causing significant dysmorphic features, bone pain, and dental anomalies. This review summarizes the pathophysiology, clinical findings, and treatment of FD, with an emphasis on the craniofacial and oral manifestations of the disease.

Cutaneous skeletal hypophosphatemia syndrome: clinical spectrum, natural history, and treatment.

Cutaneous skeletal hypophosphatemia syndrome (CSHS), caused by somatic RAS mutations, features excess fibroblast growth factor-23 (FGF23) and skeletal dysplasia. Records from 56 individuals were reviewed and demonstrated fractures, scoliosis, and non-congenital hypophosphatemia that in some cases were resolved. Phosphate and calcitriol, but not skin lesion removal, were effective at controlling hypophosphatemia. No skeletal malignancies were found. PURPOSE: CSHS is a disorder defined by the association of epidermal and/or melanocytic nevi, a mosaic skeletal dysplasia, and an FGF23-mediated hypophosphatemia. To date, somatic RAS mutations have been identified in all patients whose affected tissue has undergone DNA sequencing. However, the clinical spectrum and treatment are poorly defined in CSHS. The purpose of this study is to determine the spectrum of the phenotype, natural history of the disease, and response to treatment of hypophosphatemia. METHODS: Five CSHS subjects underwent prospective data collection at clinical research centers. A review of the literature identified 45 reports that included a total of 51 additional patients, in whom the findings were compatible with CSHS. Data on nevi subtypes, bone histology, mineral and skeletal disorders, abnormalities in other tissues, and response to treatment of hypophosphatemia were analyzed. RESULTS: Fractures, limb deformities, and scoliosis affected most CSHS subjects. Hypophosphatemia was not present at birth. Histology revealed severe osteomalacia but no other abnormalities. Skeletal dysplasia was reported in all anatomical compartments, though less frequently in the spine; there was no clear correlation between the location of nevi and the skeletal lesions. Phosphate and calcitriol supplementation was the most effective therapy for rickets. Convincing data that nevi removal improved blood phosphate levels was lacking. An age-dependent improvement in mineral abnormalities was observed. A spectrum of extra-osseous/extra-cutaneous manifestations that included both benign and malignant neoplasms was present in many subjects, though osteosarcoma remains unreported. CONCLUSION: An understanding of the spectrum, natural history, and efficacy of treatment of hypophosphatemia in CSHS may improve the care of these patients.

A phase III randomized trial of adding topical nitroglycerin to first-line chemotherapy for advanced nonsmall-cell lung cancer: the Australasian lung cancer trials group NITRO trial.

BACKGROUND: We sought to determine whether the substantial benefits of topical nitroglycerin with first-line, platinum-based, doublet chemotherapy in advanced nonsmall-cell lung cancer (NSCLC) seen in a phase II trial could be corroborated in a rigorous, multicenter, phase III trial. PATIENTS AND METHODS: Patients starting one of five, prespecified, platinum-based doublets as first-line chemotherapy for advanced NSCLC were randomly allocated treatment with or without nitroglycerin 25 mg patches for 2 days before, the day of, and 2 days after, each chemotherapy infusion. Progression-free survival (PFS) was the primary end point. RESULTS: Accrual was stopped after the first interim analysis of 270 events. Chemotherapy was predominantly with carboplatin and gemcitabine (79%) or carboplatin and paclitaxel (18%). The final analysis included 345 events in 372 participants with a median follow-up of 33 months. Topical nitroglycerin had no demonstrable effect on PFS [median 5.0 versus 4.8 months, hazard ratio (HR) = 1.07, 95% confidence interval (CI) 0.86-1.32, P = 0.55], overall survival (median 11.0 versus 10.3 months, HR = 0.99, 95% CI 0.79-1.24, P = 0.94), or objective tumor response (31% versus 30%, relative risk = 1.03, 95% CI 0.82-1.29, P = 0.81). Headache, hypotension, syncope, diarrhea, dizziness, and anorexia were more frequent in those allocated nitroglycerin. CONCLUSION: The addition of topical nitroglycerin to carboplatin-based, doublet chemotherapy in NSCLC had no demonstrable benefit and should not be used or pursued further. CLINICAL TRIALS NUMBER: Australian New Zealand Clinical Trials Registry Number ACTRN12608000588392.

Discovery of a 25-cm asteroid clast in the giant Morokweng impact crater, South Africa.

Meteorites provide a sample of Solar System bodies and so constrain the types of objects that have collided with Earth over time. Meteorites analysed to date, however, are unlikely to be representative of the entire population and it is also possible that changes in their nature have occurred with time. Large objects are widely believed to be completely melted or vaporized during high-angle impact with the Earth. Consequently, identification of large impactors relies on indirect chemical tracers, notably the platinum-group elements. Here we report the discovery of a large (25-cm), unaltered, fossil meteorite, and several smaller fragments within the impact melt of the giant (> 70 km diameter), 145-Myr-old Morokweng crater, South Africa. The large fragment (clast) resembles an LL6 chondrite breccia, but contains anomalously iron-rich silicates, Fe-Ni sulphides, and no troilite or metal. It has chondritic chromium isotope ratios and identical platinum-group element ratios to the bulk impact melt. These features allow the unambiguous characterization of an impactor at a large crater. Furthermore, the unusual composition of the meteorite suggests that the Morokweng asteroid incorporated part of the LL chondrite parent body not represented by objects at present reaching the Earth.

Hydrochemical characterization, spatial distribution, and geochemical controls on arsenic and boron in waters from arid Arica and Parinacota, northern Chile.

The livelihood of inhabitants from rural agricultural valleys in the arid Arica and Parinacota Region, northernmost Chile, strongly depends on water from high altitude rainfall and runoff to lower elevation areas. However, elevated arsenic, boron, and other potentially harmful elements compromise water quality, especially in rural areas. Samples (n = 90) of surface, underground, cold, geothermal springs, and treated and raw tap water were studied to assess water quality and to determine the main geochemical controls on water composition, origin, and geochemical evolution along dominant flowpaths. Water from major river basins across the region (Lluta, San Jose, Codpa-Chaca, Camarones and Altiplanicas) were collected for hydrogeochemical analysis of a suite of major and trace elements, δD and δ18O. Our new dataset was supplemented by hydrochemical data (n > 1500 data points) from secondary sources. Results show that 72% of the collected samples had As >10 µg/L (WHO drinking water provisional guideline) and affected 44% of the studied waters used for drinking (n = 32). Based on Chilean irrigation guidelines, elevated salinity (EC > 0.75 mS/cm) affected 80% of sampled waters, which were also impacted by high B (89% > 0.75 mg/L), and As (31% > 50 µg/L). Water composition was strongly controlled by geothermal water and freshwater mixing in high altitude areas. Magnitude and fate of As and B concentration was determined by the geothermal input type. Highest As (~21 mg/L) was associated with circum-neutral Na-Cl waters in Camarones basin, while lower As (~5 mg/L) with acid SO4 waters in Lluta basin. Additionally, evaporative concentration and sediment-water interactions were shown to control the level of As in surface and groundwaters downstream. This works provides a comprehensive analysis and a conceptual model of geochemical controls on regional water compositions, contributing to better understanding the geochemical processes underpinning the water quality challenges in northern Chile.

Multicentre phase I/II study of PI-88, a heparanase inhibitor in combination with docetaxel in patients with metastatic castrate-resistant prostate cancer.

BACKGROUND: Docetaxel (Taxotere) improve survival and prostate-specific antigen (PSA) response rates in patients with metastatic castrate-resistant prostate cancer (CRPC). We studied the combination of PI-88, an inhibitor of angiogenesis and heparanase activity, and docetaxel in chemotherapy-naive CRPC. PATIENTS AND METHODS: We conducted a multicentre open-label phase I/II trial of PI-88 in combination with docetaxel. The primary end point was PSA response. Secondary end points included toxicity, radiologic response and overall survival. Doses of PI-88 were escalated to the maximum tolerated dose; whereas docetaxel was given at a fixed 75 mg/m(2) dose every three weeks RESULTS: Twenty-one patients were enrolled in the dose-escalation component. A further 35 patients were randomly allocated to the study to evaluate the two schedules in phase II trial. The trial was stopped early by the Safety Data Review Board due to a higher-than-expected febrile neutropenia of 27%. In the pooled population, the PSA response (50% reduction) was 70%, median survival was 61 weeks (6-99 weeks) and 1-year survival was 71%. CONCLUSIONS: The regimen of docetaxel and PI-88 is active in CRPC but associated with significant haematologic toxicity. Further evaluation of different scheduling and dosing of PI-88 and docetaxel may be warranted to optimise efficacy with a more manageable safety profile.

Mineral separation protocol for accurate and precise rhenium-osmium (Re-Os) geochronology and sulphur isotope composition of individual sulphide species.

A temporal framework for mineral deposits is essential when addressing the history of their formation and conceptualizing genetic models of their origin. This knowledge is critical to understand how crust-forming processes are related to metal accumulations at specific time and conditions of Earth evolution. To this end, high-precision absolute geochronology utilising the rhenium-osmium (Re-Os) radiometric system in specific sulphide minerals is becoming a method of choice. Here, we present a procedure to obtain mineral separates of individual sulphide species that may coexist within specific mineralized horizons in ore deposits. This protocol is based on preliminary petrographic and paragenetic investigations of sulphide and gangue minerals using reflected and transmitted light microscopy. Our approach emphasizes the key role of a stepwise use of a Frantz isodynamic separator to produce mineral separates of individual sulphide species that are subsequently processed for Re-Os and sulphur isotope geochemistry.•Detailed method and its graphical illustration modified from an original procedure introduced by [1], [2].•Quality control and validation of monophasic mineral separates made by microscopic investigations and qualitative analysis of aliquots embedded in epoxy mounts.•The present method, which contributed to the successful results presented in the co-publication by Saintilan et al. (2020), demonstrates why other studies reporting Re-Os isotope data for mixtures of sulphide minerals should be considered with caution.

Maternal renal dysfunction in sheep is associated with salt insensitivity in female offspring.

To examine the programming effects of maternal renal dysfunction (created by subtotal nephrectomy in ewes prior to mating; STNx), renal and cardiovascular function were studied in 6-month-old male and female offspring of STNx and control pregnancies. After studies were conducted on a low salt diet (LSD) some female offspring underwent salt loading (0.17 M NaCl in the drinking water for 5-7 days; HSD). On LSD both male and female offspring of STNx had similar mean arterial pressures (MAP), heart rates, cardiac outputs and renal function to those measured in offspring of control ewes. In female STNx offspring on a HSD, plasma sodium levels increased and haematocrits fell, indicating volume expansion (P < 0.05). Plasma renin levels were not suppressed despite the increases in plasma sodium concentrations, but aldosterone levels were reduced. In control animals plasma renin levels fell (P < 0.05) but there was no change in plasma aldosterone concentrations. There was a positive relationship between GFR and MAP which was present only in female STNx offspring. In conclusion, in STNx offspring there was an impaired ability to regulate glomerular filtration independent of arterial pressure, renin release was insensitive to a high salt intake and control of aldosterone secretion was abnormal. This study provides evidence of abnormal programming of the renin-angiotensin system and glomerular function in offspring of pregnancies in which there is impaired maternal renal function.

The "how" and "whys" of research: life scientists' views of accountability.

OBJECTIVES: To investigate life scientists' views of accountability and the ethical and societal implications of research. DESIGN: Qualitative focus group and one-on-one interviews. PARTICIPANTS: 45 Stanford University life scientists, including graduate students, postdoctoral fellows and faculty. RESULTS: Two main themes were identified in participants' discussions of accountability: (1) the "how" of science and (2) the "why" of science. The "how" encompassed the internal conduct of research including attributes such as honesty and independence. The "why," or the motivation for conducting research, was two-tiered: first was the desire to positively impact the research community and science itself, and second was an interest in positively impacting the external community, broadly referred to as society. Participants noted that these motivations were influenced by the current systems of publications, grants and funding, thereby supporting a complex notion of boundary-setting between science and non-science. In addition, while all participants recognised the "how" of science and the two tiers of "why," scientists expressed the need to prioritise these domains of accountability. This prioritisation was related to a researcher's position in the academic career trajectory and to the researcher's subsequent "perceived proximity" to scientific or societal concerns. Our findings therefore suggest the need for institutional change to inculcate early-stage researchers with a broader awareness of the implications of their research. The peer review processes for funding and publication could be effective avenues for encouraging scientists to broaden their views of accountability to society.

Neoproterozoic copper cycling, and the rise of metazoans.

The rise of animal life is temporally related to the increased availability of oxygen in the hydrosphere and atmosphere during the Neoproterozoic. However, the earliest metazoans probably needed relatively low oxygen concentrations, suggesting additional environmental and/or biochemical developments were involved. Copper was required in the exploitation of oxygen by the evolving animals, through the development of respiratory proteins and the extracellular matrix required for structural support. We synthesize global data demonstrating a marked enrichment of copper in the Earth's crust that coincided with the biological use of oxygen, and this new biological use of copper. The copper enrichment was likely recycled into the surface environment by weathering of basalt and other magmatic rocks, at copper liberation rates up to 300 times that of typical granitic terrain. The weathering of basalts also triggered the Sturtian glaciation, which accelerated erosion. We postulate that the coincidence of a high availability of copper, along with increased oxygen levels, for the first time during the Neoproterozoic supported the critical advances of respiration and structural support in evolving animals.

Purification and characterisation of an acid phosphatase with phytase activity from Mucor hiemalis Wehmer.

An acid phosphatase with phytase activity, produced by Mucor hiemalis Wehmer, was purified to homogeneity by a combination of anion exchange, gel filtration and hydrophobic interaction chromatography. The monomeric, glycosylated enzyme displayed maximum activity at 55 degrees C and pH 5.0-5.5. When compared to commercialised products, the enzyme is more thermostable (80 degrees C, 5min), displays a broader pH versus activity profile and greater stability under simulated digestive tract conditions. Unlike commercial phytases, the Mucor enzyme should retain some activity in the small intestine as well as in the stomach, facilitating a longer duration of action and hence more extensive substrate hydrolysis. Substrate specificity studies and protein database similarity searching using mass spectrometry-derived sequence data indicate that the enzyme is an acid phosphatase with activity on phytate. Cocktails containing acid phosphatases in combination with true phytases have been shown to promote more extensive phytate degradation than do true phytases alone. This, coupled to the enzyme's functionally relevant physicochemical characteristics, suggests its likely suitability for inclusion in second generation phytase cocktails for application in animal feed.

Improving patient outcomes in fibrous dysplasia/McCune-Albright syndrome: an international multidisciplinary workshop to inform an international partnership.

To develop consensus on improving the management of patients, we convened an international workshop involving patients, clinicians, and researchers. Key findings included the diagnostic delay and variability in subsequent management with agreement to develop an international natural history study. We now invite other stakeholders to join the partnership. PURPOSE: The aim of this study was develop a consensus on how to improve the management of patients with fibrous dysplasia and prioritize areas for research METHODS: An international workshop was held over 3 days involving patients, clinicians, and researchers. Each day had a combination of formal presentations and facilitated discussions that focused on clinical pathways and research. RESULTS: The patient workshop day highlighted the variability of patients' experience in getting a diagnosis, the knowledge of general clinical staff, and understanding long-term outcomes. The research workshop prioritized collaborations that improved understanding of the contemporary natural history of fibrous dysplasia/McCune-Albright syndrome (FD/MAS). The clinical workshop outlined the key issues around diagnostics, assessment of severity, treatment and monitoring of patients. CONCLUSIONS: In spite of advances in understanding the genetic and molecular underpinnings of fibrous dysplasia/McCune-Albright syndrome, clinical management remains a challenge. From the workshop, a consensus was reached to create an international, multi-stakeholder partnership to advance research and clinical care in FD/MAS. We invite other stakeholders to join the partnership.

The evolution of tandemly repetitive DNA: recombination rules.

Variable numbers of tandem repeats (VNTRs), which include hypervariable regions, minisatellites and microsatellites, can be assigned together with satellite DNAs to define a class of noncoding tandemly repetitive DNA (TR-DNA). The evolution of TR-DNA is assumed to be driven by an unbiased recombinational process. A simulation model of unequal exchange is presented and used to investigate the evolutionary persistence of single TR-DNA lineages. Three different recombination rules are specified to govern the expansion and contraction of a TR-DNA lineage from an initial array of two repeats to, finally, a single repeat allele, which cannot participate in a misalignment and exchange process. In the absence of amplification or selection acting to bias array evolution toward expansion, the probability of attaining a target array size is a function only of the initial number of repeats. We show that the proportions of lineages attaining a targeted array size are the same irrespective of recombination rule and rate, demonstrating that our simulation model is well behaved. The time taken to attain a target array size, the persistence of the target array, and the total persistence time of repetitive array structure, are functions of the initial number of repeats, the rate of recombination, and the rules of misalignment preceding recombinational exchange. These relationships are investigated using our simulation model. While misalignment constraint is probably greatest for satellite DNA it also seems important in accounting for the evolution of VNTR loci including minisatellites. This conclusion is consistent with the observed nonrandom distributions of VNTRs and other TR-DNAs in the human genome.

A computer simulation study of VNTR population genetics: constrained recombination rules out the infinite alleles model.

Extensive allelic diversity in variable numbers of tandem repeats (VNTRs) has been discovered in the human genome. For population genetic studies of VNTRs, such as forensic applications, it is important to know whether a neutral mutation-drift balance of VNTR polymorphism can be represented by the infinite alleles model. The assumption of the infinite alleles model that each new mutant is unique is very likely to be violated by unequal sister chromatid exchange (USCE), the primary process believed to generate VNTR mutants. We show that increasing both mutation rates and misalignment constraint for intrachromosomal recombination in a computer simulation model reduces simulated VNTR diversity below the expectations of the infinite alleles model. Maximal constraint, represented as slippage of single repeats, reduces simulated VNTR diversity to levels expected from the stepwise mutation model. Although misalignment rule is the more important variable, mutation rate also has an effect. At moderate rates of USCE, simulated VNTR diversity fluctuates around infinite alleles expectation. However, if rates of USCE are high, as for hypervariable VNTRs, simulated VNTR diversity is consistently lower than predicted by the infinite alleles model. This has been observed for many VNTRs and accounted for by technical problems in distinguishing alleles of neighboring size classes. We use sampling theory to confirm the intrinsically poor fit to the infinite alleles model of both simulated VNTR diversity and observed VNTR polymorphisms sampled from two Papua New Guinean populations.