POS1229 THE IMPACT OF COVID-19 ON MEDICATION NON-ADHERENCE IN A RHEUMATOID AND PSORIATIC ARTHRITIS UK COHORT

Background

In March 2020, as part of the UK’s COVID-19 prevention strategy, those identified as ‘clinically extremely vulnerable’, were advised to shield. This included a number of patients prescribed anti-rheumatic drugs, who were asked to continue their current treatment unless they developed symptoms of infection. Suboptimal treatment adherence (16.0%-81.0%) has been reported in patients with arthritic diseases, and is associated with psychological factors, including anxiety (1). Previous literature in non-UK cohorts has highlighted suboptimal adherence levels in immunosuppressed patients during the pandemic, although many were single centre studies (2,3).

Objectives

The aim of this multi-centre study is to investigate the impact of the COVID-19 pandemic on adherence to anti-rheumatic medications in patients with established rheumatoid (RA) and psoriatic (PsA) arthritis in the UK who had recently commenced a biologic or targeted synthetic DMARD.

Methods

Between September 2020 and May 2021, RA and PsA patients prescribed biologic or targeted synthetic anti-rheumatic drugs from two multi-centre observational studies (BRAGGSS and OUTPASS) were sent a questionnaire on medication usage, adherence, and perceptions to establish the impact of COVID-19 on these parameters. Patients were asked about compliance during the COVID-19 pandemic using a 5-point Likert scale (always, often, sometimes, rarely, and never) and the reason for non-adherence. Adherence was defined as never missing or delaying a dose, unless medically advised. Descriptive summary statistics were calculated, and logistic regression and Pearson’s chi-squared tests were employed to investigate variables associated with self-reported non-adherence.

Results

In total 159 questionnaires were returned (81.1% RA and 18.9% PsA). Methotrexate (53.5%) was the most frequently prescribed agent, followed by etanercept (25.2%), sulfasalazine (22.6%), hydroxychloroquine (21.4%) and adalimumab (19.5%). Furthermore, 68.6% of patients were prescribed ≥2 drugs. During the pandemic, 42.1% of patients reported missing or delaying a treatment dose for any reason. Adherence information was available for 97.5% of patients with 25.8% reporting non-adherence which was not medically advised. Methotrexate non-adherence was 27.1%, with similar levels reported for etanercept (20.0%), sulfasalazine (27.8%), hydroxychloroquine (35.3%) and adalimumab (29.0%). No drugs had significantly different adherence compared to methotrexate. Furthermore, there was no association between disease type or perception of disease control and adherence. Of non-adherent patients, 17.5% reported increased anxiety, fear, and increased risk due to the COVID-19 pandemic as an influencing factor. Meanwhile, 37.5% of non-adherent patients listed non-COVID-19 intentional reasons and 45.0% reported non-intentional reasons, with forgetting and running out of treatment listed most frequently.

Conclusion

In a UK cohort self-reported non-adherence was reported in 25.8% of patients during the COVID-19 pandemic, despite medical advice, with reasons including increased anxiety due to COVID-19.

References

[1]Medication adherence and persistence in patients with rheumatoid arthritis, psoriasis, and psoriatic arthritis: a systematic literature review. Patient Prefer Adherence. 2018;12:1483–503.

[2]Vakirlis E, Bakirtzi K, Papadimitriou I, Vrani F, Sideris N, Lallas A, et al. Treatment adherence in psoriatic patients during COVID-19 pandemic: Real-world data from a tertiary hospital in Greece. J Eur Acad Dermatology Venereol. 2020;34(11):e673–5.

[3]Polat Ekinci A, Pehlivan G, Gökalp MO. Surveillance of psoriatic patients on biologic treatment during the COVID-19 pandemic: A single-center experience. Dermatol Ther. 2020;(December 2020):19–22.

Acknowledgements

on behalf of the BRAGGSS consortium

Disclosure of Interests

Philippa Curry: None declared, Hector Chinoy Speakers bureau: UCB, Biogen, Consultant of: Novartis, Eli Lilly, Orphazyme, Astra Zeneca, Grant/research support from: Eli Lilly, UCB, Meghna Jani: None declared, Darren Plant: None declared, Kimme Hyrich Consultant of: consultancy/honoraria from AbbVie, Grant/research support from: Pfizer, BMS, Ann Morgan Speakers bureau: Roche, Chugai, Consultant of: GSK, Roche, Chugai, AstraZeneka, Regeneron, Sanofi, Vifor, Grant/research support from: Roche, Kiniksa Pharmaceuticals, Anthony G Wilson: None declared, John Isaacs Speakers bureau: Abbvie, Gilead, Roche, UCB, Grant/research support from: GSK, Janssen, Pfizer, Andrew Morris: None declared, Anne Barton Grant/research support from: I have received grant funding from Pfizer, Galapagos, Scipher Medicine and Bristol Myers Squibb., James Bluett Grant/research support from: Pfizer Limited. JB has received travel/conference fees from UCB, Pfizer and Eli Lilly

OP0051 TRENDS FOR OPIOID PRESCRIPTIONS AMONG PATIENTS WITH RHEUMATIC AND MUSCULOSKELETAL DISEASES BETWEEN 2006-2020

Background

Opioid prescribing has contributed to a North American epidemic with increasing trends in several European countries1. Rheumatic and musculoskeletal diseases (RMDs) are one of the most common indications for prescribed opioids despite there being little evidence on opioid prescribing and the benefit of long-term use in RMDs.

Objectives

To investigate national UK opioid prescribing trends by studying the patterns of opioid prescribing in new users with the following six RMDs: rheumatoid arthritis (RA), psoriatic arthritis (PsA), axial spondyloarthritis (AxSpA), systemic lupus erythematosus (SLE), osteoarthritis (OA) and fibromyalgia.

Methods

Patients aged 18 years and older with a diagnosis of RA, PsA, AxSpA, SLE and OA with a new episode of opioid use without cancer in the Clinical Practice Research Datalink (CPRD) were included between 01/01/2006 and 31/12/2020. CPRD is a database of anonymised UK primary care electronic health records representative of the national population. New opioid users were defined as individuals with RMDs who had a new episode of opioid use in a 2-year time window up to 6 months before or after an RMD diagnosis. Rates of new opioid users were calculated by dividing the number of new opioid users with an RMD per year by the number of eligible patients registered in CPRD per year. Age- and gender-standardised rates for new opioid users were obtained using direct standardisation for each RMD. Rates of opioid prescriptions among new users for each RMD were calculated by dividing the number of opioid prescriptions among new users with an RMD in the year they had new opioid episodes by patient-years of the new users with an RMD. Trends for the rates in the study period were tested using negative binomial regression. Significant change points were identified by looking at the points where the derivative (i.e. rate of change) of the trends for the rates crossed zero. Recurrent opioid users were defined as patients who had at least 3 opioid prescriptions issued within 3 months after a new opioid episode.

Results

This study included 21,505 RA patients, 8,392 PsA patients, 4,491 AxSpA patients, 4,508 SLE patients, 944,078 OA patients, and 33,829 fibromyalgia patients, who had new opioid episodes between 2006-2020. Whilst the overall trend for RA (2.7* vs 3.9*), PsA (1.0* vs 1.8*) and fibromyalgia (3.7* vs 8.3*) has significantly increased over 15 years, from 2018 onwards, trends of new opioid users appeared to stabilise/decrease (Figure 1). The year 2018 was found to be a significant decreasing change point in the trends of new opioid users for RA, AxSpA, and SLE, whilst this was 2013 in OA and 2019 for fibromyalgia. Opioid prescription rates among new opioid users increased in SLE (4.3# vs 5.4#), OA (4.6# vs 4.9#) and fibromyalgia (5.6# vs 6.5#) but decreased in RA (5.7# vs 5.3#) from 2006 to 2020, despite fluctuations in the rates observed in this period. The highest proportions of recurrent opioid users among the 6 RMDs were patients with RA (32.6%) and fibromyalgia (31.9%).

* The number of new opioid users per 10000 persons

# The number of opioid prescriptions in new users per patient years

Figure 1.

Trends of new opioid users by RMD, 2006-2020.

Conclusion

RA, PsA and fibromyalgia had an overall increase in new opioid users since 2006. The slight decrease in the trends of new opioid users among most of the RMDs after 2018 may reflect an increasing awareness of the opioid epidemic. The high proportions of recurrent opioid users in RA and fibromyalgia patients highlight the importance of exploring the safety of long-term opioid use and effective pain interventions for patients with RMDs.

References

[1]Jani M et al (2020) Time trends and prescribing patterns of opioid drugs in UK primary care patients with non-cancer pain: A retrospective cohort study. PLoS Med 17(10): e1003270

Acknowledgements

This work was funded by a FOREUM grant (grant ID: 125059), MJ is funded through an NIHR Advanced Fellowship (NIHR301413). Thanks to the CPRD fob holders in our centre, Ruth Costello and Ramiro Bravo, for downloading the data.

Disclosure of Interests

Joyce (Yun-Ting) Huang: None declared, David Jenkins: None declared, Belay Birlie Yimer: None declared, Jose Benitez-Aurioles: None declared, Niels Peek: None declared, Mark Lunt: None declared, William Dixon Consultant of: WGD has received consultancy fees from Abbvie and Google., Meghna Jani: None declared.

OP0216 DEVELOPMENT AND VALIDATION OF PATIENT-LEVEL PREDICTION MODELS FOR ADVERSE HEALTH OUTCOMES AMONGST ADULT RA PATIENTS INITIATING FIRST-LINE TREATMENT OF METHOTREXATE MONOTHERAPY: A MULTINATIONAL REAL-WORLD COHORT ANALYSIS INCLUDING 164,735 SUBJECTS

Background:

EULAR guidelines recommend the early initiation of methotrexate (MTX) monotherapy as soon as possible after the diagnosis of rheumatoid arthritis (RA). Evaluating patient-level risks for adverse outcomes after MTX initiation would allow clinicians to provide more personalised care.

Objectives:

To develop and validate patient-level prediction models for adverse health outcomes including leukopenia, pancytopenia, infection (serious, opportunistic, all), cardiovascular disease (CVD) (myocardial infarction (MI), stroke), and cancer (breast, colorectal, uterus) in adult RA patients initiating first-line treatment of MTX monotherapy

Methods:

Health data from claims and electronic health records were used including patients from 7 European countries (Spain, Estonia, Netherlands, Belgium, Germany, France, and the UK), the United States of America, Australia, and Japan. All RA patients initiating first-line treatment of MTX monotherapy with at least one year of prior observation were included. Prediction models for the outcomes were developed for a time at risk of 3 months (infections, leukopenia, pancytopenia), 2 years (MI and stroke), and 5 years (cancers) on the Optum© De-Identified Clinformatics® Data Mart Database. Models were developed using LASSO logistic regression and were evaluated using the area under the receiver operator characteristic curve (AUROC) for discrimination and graphically assessed for calibration. The models were externally validated on all other databases.

Results:

A total of 21,307 subjects were used for training and validated against 143,427 patients from 14 sites. MI (AUROC internal 0.77, AUROC external ranging from 0.49 to 0.78), stroke (AUROC internal 0.78, AUROC external ranging from 0.68 to 0.79) and serious infection (AUROC internal 0.75, AUROC external ranging from 0.63 to 0.79) had good predictive validity [Table 1]. Discrimination for all other outcomes was lower, with all AUC<0.7 in internal validation. For detailed results see:https://data.ohdsi.org/ehdenRaPrediction/

Table 1.

Internal (Optum) and external validation results: AUC ROC for discrimination

DatabaseAcute MI within 2yStroke within 2ySerious Infection within 3mOptum (internal)0.770.780.75PanTher0.760.780.74IQVIA_AMBEMR0.760.72CCAE0.730.730.66IQVIA_GERMANY0.640.70IQVIA_THIN0.620.65MDCR0.680.680.67IQVIA_HOSPITAL0.670.630.61MDCD0.720.790.63JMDC0.490.750.71IQVIA_LPDFRANCE0.69Estonia0.670.770.82IQVIA_AUS0.58IPCI0.68SIDIAP0.650.75

Conclusion:

Clinical tools were developed that successfully identify subjects at risk of MI, stroke and serious infection at the initiation of first-line MTX therapy. The developed algorithms had good transportability and generally, the models with high AUROC had adequate internal calibration although some external validations show they could benefit from recalibration. For short-term opportunistic and all infections, as well as 5-year cancer models, we were unable to achieve a high enough AUROC to warrant validating externally.

Disclosure of Interests:

Cynthia Yang: None declared, Ross Williams: None declared, Joel Swerdel Shareholder of: J&J shares, Grant/research support from: Full-time employment salary from Janssen, Consultant of: Janssen employee, Employee of: Janssen, Paid instructor for: Janssen employee, have instructed at conferences, Speakers bureau: Janssen employee, have spoken at conferences, Meghna Jani Speakers bureau: Grifols, Talita Duarte-Salles: None declared, Katerina Chatzidionysiou Consultant of: AbbVie, Pfizer, Lilly., Daniel Prieto-Alhambra Grant/research support from: Professor Prieto-Alhambra has received research Grants from AMGEN, UCB Biopharma and Les Laboratoires Servier, Consultant of: DPA’s department has received fees for consultancy services from UCB Biopharma, Speakers bureau: DPA’s department has received fees for speaker and advisory board membership services from Amgen, Patrick Ryan: None declared, Peter Rijnbeek: None declared

FRI0120 ORAL GLUCOCORTICOID USE IS ASSOCIATED WITH HYPERTENSION IN PATIENTS WITH RHEUMATOID ARTHRITIS

Background:

Oral glucocorticoids (GC) are frequently prescribed to patients with rheumatoid arthritis (RA), however GC use is associated with a number of potential side effects. Hypertension is cited as a possible side effect, but few studies have specifically investigated GC-associated hypertension in patients with RA with conflicting results.

Objectives:

The aim of this study was to determine whether GCs were associated with an increased risk of incident hypertension in a cohort of patients with RA.

Methods:

A retrospective cohort of patients with incident RA and no hypertension at RA diagnosis were identified from UK primary care electronic health records (Clinical Practice Research Datalink). GC prescriptions were used to determine time-varying GC use and dose, categorised as: no use, >0–4.9 mg/day, 5–7.4 mg/day, 7.5–14.9 mg/day, ≥15mg/day. A 3-month risk attribution model was used where patients continued to remain at risk for 3 months after the end of prescriptions. Hypertension was identified if a patient had either: 1) 2 consecutive systolic blood pressure (BP) measurements >140mmHg within a year, 2) 2 consecutive diastolic BP measurements >90mmHg within a year or 3) antihypertensive prescriptions on at least two occasions and a Read code for hypertension. Unadjusted and adjusted Cox proportional hazards (PH) regression models were fitted to determine if there was an association between GC use and hypertension. Models were adjusted for baseline age, gender, baseline body mass index, baseline ever smoking, time-varying synthetic disease-modifying anti-rheumatic drug use, time-varying non-steroidal anti-inflammatory drug use and baseline Charlson comorbidity index.

Results:

There were 17,760 patients with incident RA and no hypertension. The cohort had a mean age of 56.3 ± 12.7 years and were predominantly female (68%). 7,421 (42%) were prescribed GCs during follow-up. There were 6,243 cases of incident hypertension over 97547 person years (pyrs) of follow-up, giving an incident rate of 64.1 per 1000 pyrs. Of those 1321 cases were in those exposed to GCs and 4922 were in those unexposed, giving incident rates of 87.6 per 1000 pyrs and 59.7 per 1000 pyrs, respectively. The adjusted Cox PH model indicated that recent GC use was associated with a 17% increased hazard of hypertension (hazard ratio: 1.17 (95% CI 1.10 to 1.24)). When categorised by dose, the adjusted model indicated only doses above 7.5mg were significantly associated with hypertension (Table 1).

Table 1.

Unadjusted and adjusted Cox proportional hazards regression model results

UnadjustedHR (95% CI)Age and gender adjustedHR (95% CI)Fully adjusted* HR (95% CI)Recent GC use1.44(1.35 to 1.53)1.23(1.16 to 1.31)1.17(1.10 to 1.24)Recent GC doseNo GC useReferenceReferenceReference>0 – 4.9mg1.35(1.21 to 1.53)1.13(1.01 to 1.28)1.10(0.98 to 1.24)5mg – 7.4mg1.40(1.22 to 1.60)1.11(0.97 to 1.27)1.07(0.93 to 1.23)7.5mg – 14.9mg1.44(1.33 to 1.57)1.26(1.16 to 1.38)1.18(1.08 to 1.29)15mg and over1.60(1.40 to 1.84)1.45(1.27 to 1.66)1.36(1.18 to 1.56)

* Adjusted for: Baseline age, gender, baseline body mass index, baseline ever smoking, synthetic disease-modifying anti-rheumatic drug use (time-varying), non-steroidal anti-inflammatory drug use (time-varying) and baseline Charlson comorbidity index.

Conclusion:

In this large cohort of patients with RA and without hypertension, recent GC use was associated with incident hypertension. In particular doses ≥7.5mg were associated with hypertension while the association with lower doses was inconclusive. Clinicians need to consider cardiovascular risk when prescribing GCs and ensure BP is regularly monitored.

Disclosure of Interests:

Ruth E Costello: None declared, Belay Birlie Yimer: None declared, Meghna Jani Speakers bureau: Grifols, William Dixon Consultant of: Bayer and Google

OP0087 NATIONAL VARIATION AND FACTORS ASSOCIATED WITH THE TRANSITION FROM FIRST USE TO LONG-TERM OPIOID USE FOR NON-CANCER PAIN

Background:

Prescribing behaviour of physicians has been described as a key driver of rising opioid prescriptions and long-term opioid use. However, the effect of prescribers requires interpretation within context. No studies have investigated the extent to which regions, practices and prescribers, vary in opioid prescribing accounting for case-mix by considering this hierarchy together.

Objectives:

(i) Quantify and identify risk factors for the transition from new-user to long-term opioid user (ii) Quantify variation of long-term use attributed to region, practice and prescriber, accounting for patient mix and chance variation.

Methods:

We conducted a retrospective observational UK study between 2006-2017 using Clinical Practice Research Datalink. Opioids new users, ≥18 years, without cancer were identified. Long-term opioid use was defined as ≥3 opioid prescriptions issued within a 90-day period from index date, or ≥1 opioid prescription lasting at least 90 days in the first year. A multi-level random-effects logistic regression model was used to examine the association of patient characteristics with the odds of becoming a long-term opioid user. To examine variation in opioid use amongst prescribers, GP practices and region after adjusting for patient case-mix, we used a nested random-effect structure. A ‘high-risk’ region, prescriber or practice was defined as those where the entire adjusted 95% CI lay above the population average.

Results:

1,968,742 new opioid users were included; 14.6% patients transitioned to long-term use. In the fully adjusted model, factors associated with higher odds of long-term opioid use included high morphine milligram equivalents (MME)/day at first prescription, older age, deprivation, fibromyalgia, rheumatological conditions, major surgery (Table). After adjustment for case-mix, the North-West, Yorkshire and South-West were found to be high-risk regions for long-term use. 103 practices (25.6%) and 540 prescribers (3.5%) were associated with a significantly higher risk of long-term use. The odds of becoming a long-term user for a patient belonging to these prescribers reached up to >3.5 times than the population average.

Conclusion:

Prescribing factors, age, deprivation and conditions including fibromyalgia and rheumatological conditions were associated with higher odds of long-term opioid use. In the first UK study evaluating long-term opioid prescribing with adjustment for patient-level characteristics, variation in regions and especially practices and prescribers were observed. Our findings support greater calls for action to reduce practice and prescriber variation by promoting safe practice in opioid prescribing.

Table.

Factors associated with long-term opioid use using a multi-level model accounting for clustering of individuals within prescriber, practice and region

Individual factorsAdjusted Odds Ratio (95% CI) *Prescribing factorsIndex daily MME >2007.59 (6.29, 9.16)Index daily MME 100-2001.12 (1.03, 1.21)Index daily MME 50-1001.58 (1.49, 1.68)Index daily MME <50RefGabapentinoid use2.51 (2.43, 2.60)Psychotropic use1.28 (1.17, 1.40)Age>754.35 (4.26, 4.45)65-753.57 (3.50, 3.65)55-653.03 (2.96, 3.09)35-551.91 (1.88, 1.95)Age <35RefDeprivation (Townsend score)Quintile 5 (Most deprived)1.54 (1.51, 1.57)Quintile 41.34 (1.31, 1.36)Quintile 31.20 (1.18, 1.22)Quintile 21.09 (1.07, 1.11)Quintile 1 (Least deprived)RefPre-existing conditions/ prior proceduresFibromyalgia1.81 (1.49, 2.20)Substance use disorder1.76 (1.70, 1.83)Suicide and self-harm1.56 (1.51, 1.61)Rheumatological conditions Ψ1.54 (1.49, 1.59)Alcohol abuse1.50 (1.45, 1.55)Depression1.28 (1.26, 1.30)Major Surgery1.09 (1.06, 1.13)

Abbreviations: MME, Morphine Milligram Equivalent; *p<0.05. Index daily MME/day is the MME/day at first prescription (MME= daily dose in milligrams X opioid conversion ratio). Ψ Defined by Charlson score including rheumatoid arthritis, SLE, myositis.

Disclosure of Interests:

Meghna Jani Speakers bureau: Grifols, Belay Birlie Yimer: None declared, Therese Sheppard: None declared, Mark Lunt: None declared, William Dixon Consultant of: Bayer and Google

Primary percutaneous coronary intervention for acute ST elevation myocardial infarction--first year's experience of a tertiary referral centre in the UK

This study evaluated the first year's experience of a large interventional centre in the UK after a primary percutaneous coronary intervention (PCI) programme that runs 24 hours a day and seven days a week was started. Workload, patient outcome, length of stay, and effect on the remainder of the interventional service were analysed. The primary PCI service for a mainly urban population of 800,000 was started in April 2005. All relevant characteristics, details of procedures, outcome, and other data on quality of care were collected and entered prospectively onto a computerised database. Data were analysed with SPSS (version 13.0). Over a 12-month period, 305 patients were diagnosed with ST elevation myocardial infarction (STEMI), of whom 259 (85%) were accepted for primary PCI. Median door-to-balloon time was 98 minutes, which decreased from 106 minutes in the first six months to 93 minutes in the second six months (p < 0.005). In-hospital mortality was 4.5% and 30-day mortality was 4.9%. Median length of stay was three days, which was reduced from the six days previously reported after thrombolysis. Waiting times for other acute and elective PCI procedures did not increase after initiation of the primary PCI programme. Primary PCI can be delivered successfully in a setting in the UK with low mortality and reduced length of stay and without a negative impact on other interventional services.

Leflunomide and its metabolite A771726 are high affinity substrates of BCRP: implications for drug resistance

BACKGROUND

Earlier publications have suggested a possible role for the efflux transporter breast cancer resistance protein (BCRP) in acquired resistance to disease-modifying antirheumatic drugs (DMARDs) such as leflunomide and its metabolite A771726 (teriflunomide). However, there is no direct evidence that BCRP interacts with these drugs.

OBJECTIVES

To characterise the interaction between BCRP transporter and leflunomide and its active metabolite A771726, with emphasis on the nature of the interaction (substrate or inhibitor) and the kinetic characterisation of the interactions.

METHODS

Different in vitro membrane-based methods (ATPase and vesicular transport assay) using BCRP-HAM-Sf9 membrane preparations and cellular assays (Hoechst assay and cytotoxicity assay) were performed on PLB985-BCRP and HEK293-BCRP cell lines overexpressing BCRP.

RESULTS

In all assays used, an interaction between the investigated drugs and BCRP was detected. In the vesicular transport assay, both leflunomide and its metabolite inhibited BCRP-mediated methotrexate transport. Both compounds are likely substrates of BCRP as shown by the vanadate-sensitive ATPase assay. In line with the membrane assays, leflunomide and A771726 inhibited BCRP-mediated Hoechst efflux from PLB985-BCRP cells. In the cytotoxicity assay, overexpression of BCRP conferred 20.6-fold and 7.5-fold resistance to HEK293 cells against leflunomide and A771726, respectively. The resistance could be reversed by Ko134, a specific inhibitor of BCRP.

CONCLUSION

Based on these results, BCRP could play an important role in the resistance to leflunomide and A771726 via interactions with these drugs. BCRP may also mediate drug-drug interactions when leflunomide is administered with other BCRP substrate drugs such as methotrexate.

Room-temperature lasing of end-pumped Ho:Lu(3)Al(5)O(12)

Room-temperature lasing at 2.1-microm has been demonstrated in Ho:Lu(3)Al(5)O(12) with a slope efficiency of 82% and a threshold energy of 4.4 mJ. A maximum absorbed energy of 17 mJ yielded 10 mJ of laser output energy. To simulate diode-pumping experiments, a tunable Co:MgF(2) laser operating at 1.878 microm was used to achieve lasing on (5)I(7) ? (5)I(8) transitions.

Molecular characterization of a deleted X chromosome (Xq13.3-Xq21.31) exhibiting random X inactivation

As a result of selection following random X chromosome inactivation in human females, X chromosomes with visible deletions are usually inactive in every somatic cell. We have studied a female with mental retardation and dysmorphic features whose karyotype includes an X chromosome with a visible interstitial deletion in the proximal long arm. Based on cytogenetic analysis, the proximal breakpoint appeared to be in band Xq13.1, and the distal one in band q21.3. However, molecular analyses show that less of the q13 band is missing than cytogenetic studies indicated, as the deletion includes only loci from the region Xq13.3 to Xq21.31. Unexpectedly, studies of chromosome replication show that the pattern of X inactivation is random. Whereas the deleted X chromosome is late replicating in some cells from all tissues studied, it is early replicating in the majority of blood lymphocytes and skin fibroblasts, and is the active X chromosome in many of the hybrids derived from skin fibroblasts. As this chromosome is able to inactivate, it must include those DNA sequences from the X-inactivation center (XIC) that are essential for cis X inactivation. Molecular studies show that the XIC region, at Xq13.2, is present, so it is unlikely that the lack of consistent inactivation of this chromosome is attributable to close proximity of the breakpoint to the XIC. Supporting this conclusion is the similarity of the breakpoints to those of the other chromosomes we studied, whose deletions clearly do not interfere with the ability to inactivate. Our results show that deletions distal to DXS441 in Xq13.2 do not interfere with cis X inactivation. We attribute the random pattern of X inactivation reported here to the fact that in the tissues studied, cells with this interstitial deletion are not at a selective disadvantage.

The severe phenotype of females with tiny ring X chromosomes is associated with inability of these chromosomes to undergo X inactivation

Mental retardation and a constellation of congenital malformations not usually associated with Turner syndrome are seen in some females with a mosaic 45,X/46,X,r(X) karyotype. Studies of these females show that the XIST locus on their tiny ring X chromosomes is either not present or not expressed. As XIST transcription is well correlated with inactivation of the X chromosome in female somatic cells and spermatogonia, nonexpression of the locus even when it is present suggests that these chromosomes are transcriptionally active. We examined the transcriptional activity of ring X chromosomes lacking XIST expression (XISTE-), from three females with severe phenotypes. The two tiny ring X chromosomes studied with an antibody specific for the acetylated isoforms of histone H4 marking transcribed chromatin domains were labeled at a level consistent with their being active. We also examined tow of the XISTE- ring chromosomes to determine whether genes that are normally silent on an inactive X are expressed from these chromosomes. Analyses of hybrid cells show that TIMP, ZXDA, and ZXDB loci on the proximal short arm, and AR and PHKA1 loci on the long arm, are well expressed from the tiny ring X chromosome lacking XIST DNA. Studies of the ring chromosome that has XIST DNA but does not transcribe it show that its AR allele is transcribed along with the one on the normal X allele.(ABSTRACT TRUNCATED AT 250 WORDS)

Deficient transcription of XIST from tiny ring X chromosomes in females with severe phenotypes

The severe phenotype of human females whose karyotype includes tiny ring X chromosomes has been attributed to the inability of the small ring X chromosome to inactivate. The XIST locus is expressed only from the inactive X chromosome, resides at the putative X inactivation center, and is considered a prime player in the initiation of mammalian X dosage compensation. Using PCR, Southern blot analysis, and in situ hybridization, we have looked for the presence of the XIST locus in tiny ring X chromosomes from eight females who have multiple congenital malformations and severe mental retardation. Our studies reveal heterogeneity within this group; some rings lack the XIST locus, while others have sequences homologous to probes for XIST. However, in the latter, the locus is either not expressed or negligibly expressed, based on reverse transcription-PCR analysis. Therefore, what these tiny ring chromosomes have in common is a level of XIST transcription comparable to an active X. As XIST transcription is an indicator of X chromosome inactivity, the absence of XIST transcription strongly suggests that tiny ring X chromosomes in females with severe phenotypes are mutants in the X chromosome inactivation pathway and that the inability of these rings to inactivate is responsible for the severe phenotypes.