Mitral valve abnormalities in decedents of sudden cardiac death due to hypertrophic cardiomyopathy and idiopathic left ventricular hypertrophy

Background

The sole identification of left ventricular hypertrophy (LVH) in a young individual that died suddenly may often lead to an erroneous diagnosis of hypertrophic cardiomyopathy (HCM). Emerging data suggests that idiopathic LVH (ILVH) and HCM may be separate entities.

Aim

We aimed to report on the prevalence and nature of mitral valve (MV) abnormalities, in a cohort of sudden cardiac death (SCD) victims with a post-mortem examination consistent with HCM and ILVH.

Methods

We reviewed 6860 consecutive cases of SCD referred to our specialist cardiac pathology centre between 1994 and 2020. SCD was defined as death from a cardiovascular cause within 12 hours of apparent well-being. HCM was defined by the presence of LVH, in the absence of abnormal loading conditions and characterised by myocyte disarray at histology. ILVH was defined as unexplained LVH (heart weight >500 g in males and >400 g in females) and left ventricular (LV) wall thickness >15mm, in the absence of myocardial disarray or secondary causes of LVH. The MV was examined for patency, circumference, thickening, nodularity, ballooning, bulging between cords, perforation, and the presence of impact lesions in the LV outflow tract (LVOT) and aortic outlet.

Results

Of the total cases of SCD, 264 (4%) were due to HCM (mean age 41±18 years, 78% males, LV maximal wall thickness 19±6 mm) (Figure 1). Ante-mortem symptoms were reported in 44 (17%) cases and for the majority (n=217, 82%) HCM was established at post-mortem. Death was attributed to ILVH in 253 (3%) cases (mean age 43±16 years, 80% males, LV maximal wall thickness 18±4 mm). MV abnormalities were found in 58 (22%) decedents with HCM (mean age 38±17 years; 72% males) and in 13 (5%) decedents with ILVH (mean age 55±15 years; 77% male), p<0.001. Amongst the 58 (22%) cases with HCM and MV abnormalities, 15 (6%) cases had multiple MV abnormalities. These included impact lesions associated with thickening of the anterior leaflet of the MV (n=39) and degenerative changes (n=34) such as bulging and ballooning; and thickening and nodularity. Decedents with HCM exhibiting MV abnormalities were younger than decedents with a normal MV (38±17 versus 45±19 years; p=0.08). Among the 253 decedents with ILVH, 13 (5%) cases exhibited MV abnormalities, which largely included degenerative changes (n=12). Among decedents with HCM and ILVH exhibiting MV abnormalities, the former was significantly younger (38±17 versus 55±15; p=0.001). Myocardial fibrosis was observed in 162 (61%) cases of HCM and 99 (39%) cases of ILVH, p<0.001.

Conclusions

MV abnormalities are over four-fold more common in individuals with HCM than those with ILVH and may be considered as additional macroscopic features to differentiate between these two entities. Furthermore, the inherent descriptive terminologies used when assessing the MV, support a greater emphasis on the standardisation and quantification of MV abnormalities as part of the autopsy in victims of SCD.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): Acknowledgements: We thank the charitable organisation, Cardiac Risk in the Young (CRY) who fund and support the CRY Cardiovascular Pathology Unit and CRY database.

Sudden cardiac death during exercise in young individuals with hypertrophic cardiomyopathy

Background

Sudden cardiac death (SCD) in young individuals and athletes is generally caused by hereditary cardiac conditions, including cardiomyopathies such as hypertrophic cardiomyopathy (HCM). Although historically HCM has been reported as the predominant cause of SCD in young athletes, it is unclear as to what degree exercise is a trigger for possible fatal arrhythmias.

Aim

We aimed to report on the circumstances of SCD in a cohort of young individuals aged ≥10 and <30 whose autopsy was consistent with HCM.

Methods

We reviewed 6860 consecutive cases of SCD referred to our specialist cardiac pathology centre 1994 and 2020. SCD was defined as death from a cardiovascular cause within 12 hours of apparent well-being. All cases underwent detailed autopsy evaluation of the heart, including histological analysis, by expert cardiac pathologists. A minimum of 10 blocks of tissue were taken for histological analysis. HCM was defined by the presence of increased heart weight or increased wall thickness and significant myocyte disarray at histological examination.

Results

Of the total cases of SCD, 264 (4%) were due to HCM. Our cohort of young decedents comprised of 66 individuals (average age 21±5 years, males 76%). For the majority (n=52, 79%) SCD was the first manifestation of HCM. The average heart weight was 507±152 grams and left ventricular (LV) fibrosis was found in 28 (42%) cases (Figure 1A). Death was more common between 16 and 20 years of age (n=24) (Figure 1B). Death occurred during exertion in 25 (38%) individuals and at rest or during daily activities in the remaining 41 (62%), including 5 individuals who died during sleep. Male sex was more represented among decedents who died during exertion (88% compared with 68% in the group that died at rest, p=0.07); LV fibrosis was more commonly observed in individuals who died during exertion (56% compared with 34% in the group who died at rest, p=0.08). Younger individuals between 10–15 years of age died mostly during exercise (80%), in other age groups death occurred mainly at rest (33% in age group 16–20 years, 30% in age group 21–25 years, 33% in age group 26–30 years) (Figure 1B).

Conclusions

We observed a high age-related variability in terms of circumstances of death. In the context of HCM, our findings suggest that individuals aged 10–15 years are the most vulnerable in terms of exercise-related-SCD. This exemplifies the importance of preventative cardiac screening in young individuals who might be harbouring quiescent cardiac conditions associated with young SCD.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): Acknowledgements: We thank the charitable organisation, Cardiac Risk in the Young (CRY) who fund and support the CRY Cardiovascular Pathology Unit and CRY database.

A positive toxicology screen is a rare finding in sports-related sudden cardiac deaths

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): University of Copenhagen

Introduction

Sports-related sudden cardiac deaths (SrSCD) are rare events often occurring in healthy individuals. An underlying cardiac disease may, in combination with strenuous exercise, trigger lethal arrhythmias. Intake of drugs (legal and illicit) increases the risk of sudden cardiac death (SCD), but knowledge on toxicological findings in SrSCD remains sparse.

Purpose

This study aimed to characterize the SrSCD population in an international consortium by investigating the epidemiology and autopsy findings in SrSCD.

Methods

Participating centers of the consortium (Denmark, Australia, England, Spain) provided data on all forensically autopsied SCDs aged 12—49 years in their respective cohorts, spanning from 2000—2019. Demographics, autopsy findings, and toxicology screen were assessed. A toxicology screen was considered positive if any drug was detected, except drugs related to resuscitation.

Results

Of all 5,029 SCDs, we identified 435 (9%) SrSCD. The majority (88%) died during sports while the remaining 12% died within one hour from exercise. SrSCD occurred more often in males (91% vs 71%, p<0.001) who were younger (32 vs 36 years). In SrSCD, the autopsy more frequently revealed an underlying structural cardiac cause of death (64% vs 54%, p<0.001); the most frequent causes of death among SrSCDs were sudden unexpected death (SUD), ischemic heart disease (IHD), and arrhythmogenic cardiomyopathy (ACM). Toxicological screens were performed in approx. 90% of cases, regardless of relation to sport. Among SrSCD cases, the rate of a positive toxicology was less than half compared to other SCDs (18% vs 44%, p<0.001). The most frequent toxicological findings among SrSCDs were ethanol, central stimulants, cannabinoids, and non-opioid analgesics.

Conclusions

Sports-related SCD accounted for 9% of all SCDs in our population aged 12—49 years. The majority of sports-related deaths (88%) occurred during exercise activity. SrSCDs more often had an underlying structural cardiac disease, mainly IHD and ACM. Positive toxicology screens were half as frequent in SrSCDs compared with non-SrSCDs.

Six-month outcomes of a high intensity exercise programme in young patients with hypertrophic cardiomyopathy: The SAFE-HCM trial

Funding Acknowledgements

Type of funding sources: Other. Main funding source(s): Cardiac Risk in the Young

Background

Moderate intensity exercise training in older patients with hypertrophic cardiomyopathy (HCM) can improve functional capacity, without significant harm. However, younger patients are attracted to high intensity training (HIT) regimes. The SAFE-HCM study demonstrated that an individually tailored, HIT programme in young patients with HCM was feasible, and provided both health and psychological benefits, without an increase in the burden of arrhythmia.

Purpose

To assess whether observed benefits of a HIT programme in young patients with HCM are sustained at 6 months.

Methods

Eighty patients with HCM (45.7y+/-8.6) underwent baseline clinical and psychological assessment. Individuals were randomised to a 12-week HIT programme (n = 40) or usual care (n = 40). Baseline evaluation was repeated at 12 weeks (T12). Feasibility, safety, health and psychological benefits were assessed. At 12-weeks individuals were encouraged to continue with the frequency and intensity of physical activity (PA) achieved at the end of the cardiac rehabilitation programme. Participants in the exercise arm were invited to follow-up at 6 months (T6m).

Results

The majority (83%) of participants completed the 12-week study. At T12 there was no significant difference between groups in the composite arrhythmia safety outcome (p = 0.99). The indices of exercise capacity were significantly improved in the exercise compared to the control group; peak VO2 (+3.7ml/kg/min [CI 1.1,6.3], p = 0.006), VO2/kg at anaerobic threshold (VO2/kgAT) (+2.44ml/kg/min [CI 0.6,4.2], p = 0.009), time to AT (+115s [CI 54.3,175.9], p < 0.001) and exercise time (max ET) (+108s [CI 33.7,182.2], p = 0.005). The exercise group also demonstrated greater reduction in systolic BP (-7.3mmHg [CI -11.7,-2.8], p = 0.002), BMI (-0.8kg/m2 [CI-1.1,-0.4], p < 0.001), anxiety (-2.6 [CI-3.6,-1.6], p= <0.001) and depression (-1.1 [CI -2.0,-0.2], p = 0.015) scores. At T6m patient reported exercise adherence was comparable to baseline PA in 33/34 of the exercise group attending for follow up. Most exercise gains dissipated with the exception of time to AT (p = 0.002), max ET (p = 0.003), VO2/kgAT (p = 0.04) and anxiety score (p < 0.001) (Figure 1). There were no sustained episodes of atrial or ventricular arrhythmias. The incidence of NSVT did not differ between time points (p = 0.09).

Conclusion

A 12-week HIT programme in young patients with HCM offers considerable gains in fitness and psychological outcomes, with no increase in arrhythmic burden. At T6m exercise levels as well as most physiological adaptations and health benefits returned to baseline, as seen in other studies when formal participation in an exercise programme comes to an end. This highlights the importance of the implementation of strategies to encourage ongoing engagement in PA. Potential solutions include identification of barriers to exercise, as well as adoption of novel tele-rehabilation approaches.

Abstract Figure 1 Sustained benefits at T6m

Cardiovascular phenotyping of the first mouse model of Sarcoidosis

Introduction

Sarcoidosis is a potentially life-threatening, inflammatory, granulomatous disease that affects multiple organs including the heart. Heretofore, its unknown etiology had hindered the creation of experimental models and the understanding of the molecular mechanisms of pathogenesis behind it.

Purpose

To extensively phenotype the heart of the first mouse model of sarcoidosis created through deletion of the tuberous sclerosis 2 (Tsc2) gene in the CD11c-positive macrophage population.

Methods

Tsc2 fl/fl CD11c Cre+ (Tsc2-KO; n=7) and Tsc2 fl/fl CD11c Cre- (Tsc2-WT; n=7) mice were subjected to echocardiography at 25 weeks of age (woa) to assess myocardial dimensions and function. Hearts of 13 and 25woa animals were subjected to histological and immunological stains to assess tissue changes, subtype inflammatory infiltrates and examine the localization of key proteins shown to be re-distributed in patients.

Results

At 13 woa, Tsc2-KO animals show inflammatory infiltrates; subtyped mainly as macrophages as well as evidence of myocyte destruction. At 25 woa, the number of inflammatory cells is significantly higher and there is heavy fibrotic replacement primarily in the septum and trabeculae. Older animals also show giant cells and non-necrotizing granulomas. The hearts show heterogeneous gap junction remodeling known to constitute an arrhythmogenic substrate and lack of immunoreactive signal for the desmosomal protein plakoglobin from the cell-cell junctions just as described in patients. The left ventricular ejection fraction and LV morphology was not significantly different between the two groups (EF: 64±4% in Tsc2-KO vs 64±2% in Tsc2-WT; LV end-systolic diameter: 4.51±0.54 mm in Tsc2-KO vs 4.59±0.29 mm in Tsc2-WT). However, there was a strong trend towards increasing filling pressure (E/e'ratio; 14.24±4.01 vs 12.15±2.54) and mean pulmonary pressure (21±6 vs 18±3 mmHg) in Tsc2-KO mice compared to controls suggesting diastolic dysfunction.

Conclusion

Hearts of the Tsc2 fl/fl CD11c Cre+ animals show a phenotype highly reminiscent of cardiac sarcoidosis in patients. We anticipate that this model will be very useful in deciphering molecular mechanisms of pathogenesis as well as testing much-needed mechanism-based therapies.

Funding Acknowledgement

Type of funding source: Foundation. Main funding source(s): British Heart Foundation - PG/18/27/33616

Safety and outcomes of a structured exercise programme in young patients with hypertrophic cardiomyopathy: the SAFE-HCM trial

Background

Contemporary studies in hypertrophic cardiomyopathy (HCM) suggest that moderate intensity exercise can improve cardiorespiratory fitness without raising significant safety concerns. Although low/moderate intensity exercise may be appropriate for older HCM patients, it is unlikely to attract younger, often asymptomatic patients, who wish to engage in higher intensity regimes.

Purpose

To assess the feasibility, safety and outcomes of an individually tailored, high intensity exercise programme in young patients with HCM.

Methods

In this RCT, 80 patients with HCM, aged 16–60 (mean 45.7, [SD8.6]) underwent baseline testing with ECG, echocardiography, blood testing, exercise testing, 48-hour ECG and psychological assessment. Individuals were randomised to a 12-week supervised exercise programme (HRR increased from 70–85%) (n=40) or usual activity (n=40). Baseline investigations were repeated at 12 weeks.

Feasibility was assessed by a) recruitment, adherence and retention rates; b) staffing ratios and logistics; c) acceptability of the intervention/educational materials. Safety was assessed as a composite of 1) cardiovascular death, 2) cardiac arrest, 3) device therapy, 4) exercise induced syncope, 5) sustained/non-sustained (NS) ventricular tachycardia (VT) or 6) sustained atrial arrhythmias. Secondary outcomes included health and psychological benefits.

Results

67 individuals (82.5%) completed the study. Reasons for refusal included travel, work and family commitments. The majority (64.7%) of exercising individuals progressed to 85%HRR. Resource requirements were similar to other programmes. All individuals felt supported, more confident to exercise, and found educational materials clear and informative.

There was no significant difference between groups for the composite safety outcome. One individual experienced exercise induced syncope due to ventricular standstill (exercise) and another sustained VT (control). Both required device implantation. There was no significant difference between groups in episodes of NSVT (p=0.573) or ectopic burden (p=0.729).

At 12 weeks, exercise group participants demonstrated greater activity levels (+1.1 hours [CI 0.2–2.1], p=0.024). The change in peak aerobic capacity (+255.2ml/min [CI 93.2–417.1], p=0.003), time to anaerobic threshold (AT) (+115s [CI 54.2–176.0], p<0.001), total exercise time (+108.1s [CI 33.1–183.0], p=0.005) and oxygen uptake at AT (+2.44ml/kg/min [CI 0.6–4.2], p=0.009) were all significantly greater in the exercise group. HADS anxiety (p<0.001) and depression (p=0.017) scores demonstrated the greatest reduction in the exercise group.

Conclusions

A high intensity exercise programme is feasible in young patients with HCM, with considerable gains in cardiorespiratory fitness and psychological outcomes. Importantly, arrhythmia burden was not increased in the exercise group. Further research is still required to assess the long-term safety of high intensity exercise in the HCM population.

Funding Acknowledgement

Type of funding source: Other. Main funding source(s): Cardiac Risk in the Young

P890Gene carriers of hypertrophic cardiomyopathy, what to expect over time

Background

Data on the natural history of genotype positive/phenotype negative (G+/P-) hypertrophic cardiomyopathy (HCM) patients identified as a part of genetic cascade screening in different age groups is limited.

Purpose

To describe the rate of conversion to overt HCM phenotype in G+/P- subjects in relation with the age who were identified in a specialized clinic in a single center.

Methods

We retrospectively identified 56 consecutive HCM G+/P− subjects followed in our center specialized clinic between Jan 2012-Jan 2019. Demographics, family history of sudden cardiac death (SCD) and presence of symptoms were collected. All of them underwent baseline investigations including ECG, echocardiogram and/or cardiac magnetic resonance (CMR) and 24 hour monitor at baseline and during follow up. Overt HCM phenotype was defined as left ventricular hypertrophy (LVH) ≥13mm in the echocardiogram or CMR.

Results

We identified 56 HCM G+/P− subjects from 34 different families. 22 subjects were ≤18 years old with a mean age of 11.6±0.9 years (IQR [P25-P75] 9–16 years) and 32 subjects were >18 years old with a mean age of 38.1±2.2 years (IQR [P25-P75] 27–48 years). Mean time of follow up was 35.2±34.4 months (IQR [P25-P75] 4.25–50.25 years). 60.7% (34) of them were female and 82.1% (46) were of Caucasian ethnicity. Most of the subjects with no evidence LVH were asymptomatic but small number had symptoms, 8.9% (5), and 3.6% (2) were treated with betablockers for palpitations. Family history of SCD was present in 57.1% (32) of the subjects and 35.7% (20) had a relative with an implantable cardiac defibrillator (ICD). MYBPC3 gene mutations were identified in 62.5% (35) of subjects, followed by MYH7 gene mutation in 23.2% (13) of the cases.

None of the subjects under 18 year old developed HCM during the period of observation, however 7 subjects (21.9%), mean age 48.6±10.5 years, 71.4% (5) females, showed progression to HCM in the >18 years old group. All of them had pathogenic MYBPC3 gene variants. No differences were found in gender, ethnicity, symptoms or family history of SCD in the G+/P− vs HCM group. There were no differences on the presence of ECG abnormalities and no episodes of NSVT were recorded in any of the groups. Baseline E/e' values of those with new HCM vs G+/P− were higher (8.2±3.3 vs 5.6±1.7, p=0.014).

Conclusions

In our cohort, rate of progression to HCM phenotype was 21.9% of >18 years old HCM G+/P- subjects. The mean age at the time of developing the phenotype was 48.6±10.5 years old and all the patients were asymptomatic for cardiac symptoms. Echocardiographic E/e' values were increased. This data supports the need of life long follow up of this group of patients with ongoing clinical evaluation.

Acknowledgement/Funding

ESC clinical grant

P3683Diagnosis of arrhythmogenic cardiomyopathy and overlap with cardiac adaptation to exercise: insights from a cardiac magnetic resonance study

Background

The diagnosis of arrhythmogenic right ventricular cardiomyopathy (ARVC) is often challenging and some structural abnormalities typical of the disease may overlap with changes reflective of cardiac adaptation to exercise.

Purpose

The aim of the study was to assess the performance of the cardiac magnetic resonance (CMR) 2010 Task Force Criteria (TFC) in a cohort of patients with definite diagnosis of ARVC and define the overlap with a cohort of highly trained athletes of similar age and sex.

Methods

We compared the CMR features of 43 patients (mean age 49±17 years, 49% males, 32 (74%) genotyped) with a definite diagnosis of ARVC according to the revised TFC to 97 (mean age 45±16 years, 61% males) highly-trained athletes of similar age and sex, in whom cardiac disease was excluded after comprehensive work-up.

Results

The CMR was abnormal in 37 (86%) patients. The right ventricle (RV) was affected in isolation in 17 (39%) patients, with 18 (42%) patients exhibiting biventricular involvement and 2 (5%) patients showing isolated left ventricular (LV) involvement. The most common RV abnormalities were regional wall motion abnormalities (RWMA) (n=34; 79%), RV dilatation fulfilling a major or minor volume TFC (n=18; 42%), impaired systolic function (RV ejection fraction (EF) ≤45%: n=17; 40%) and myocardial fibrosis (n=13; 30%). The predominant LV abnormality was myocardial fibrosis (n=20; 47%), with a small proportion of patients exhibiting RWMA (n=6; 14%) and impaired systolic function (LVEF <50%: n=6; 14%). Twenty-three (53%) patients fulfilled a major (n=14; 32%) or a minor (n=9; 21%) CMR TFC. Sixteen (16%) athletes exceeded the cut-off values for RV volumes used as a major (n=10; 10%) or a minor (n=6; 6%) TFC with an inverse relationship between age and RV volumes (r=−41, p=0.001). None of the athletes fulfilled the TFC for RV ejection fraction. Applying the CMR TFC to the ARVC patient population showed a sensitivity of 33% for the major and 28% for the minor criteria. Applying the RV volume and systolic function TFC values in the entire study population showed a sensitivity of 53%, a specificity between 83% and an accuracy of 0.68.

Conclusions

The great majority (86%) of patients with ARVC demonstrates structural abnormalities suggestive of cardiomyopathy on CMR but only 53% fulfills any of the CMR TFC. Only a small proportion (16%) of older athletes demonstrate significant RV dilatation that overlaps with the volume criteria for ARVC, in juxtaposition to younger athletes who exhibit a greater degree of overlap. The emergence of ARVC as a biventricular disease provides an opportunity to re-evaluate the diagnostic criteria and include LV involvement in conjunction with RV involvement to improve diagnostic accuracy.

Acknowledgement/Funding

CRY (Cardiac Risk in the Young) charity

Getting to the heart of the matter: investigating the idiopathic sudden cardiac death of a previous well soldier

A 25-year-old infantry soldier, who was previously fit and well, had a cardiac arrest while undertaking an advanced fitness test. Despite early cardiopulmonary resuscitation by colleagues and the emergency services, he was later pronounced dead. A postmortem performed by an expert pathologist and a toxicology screen were normal and the death was attributed to sudden arrhythmic death syndrome (SADS). Screening of his family in our Inherited Cardiac Conditions clinic identified Brugada syndrome (BrS) in two first-degree relatives. This case generates discussion on sudden cardiac death, family screening in SADS, BrS and the limitations of recruit screening with an ECG.

The phenotype standardization project: improving pharmacogenetic studies of serious adverse drug reactions

The ability to predict the risk for serious drug-induced adverse reactions first requires a large patient database for characterization and validation of genetic markers. The Phenotype Standardization Project (PSP) was initiated to standardize phenotypic definitions, thereby facilitating much-needed recruitment without sacrificing the reliability of patient classification. Three phenotypes have been considered in this initial phase: drug-induced liver injury, drug-induced skin injury, and drug-induced torsade de pointes.

The negative effect of red tape on research

PURPOSES

To describe the kind of the difficulties encountered when seeking research governance approval for a nationwide public health and genetic study-the Drug-Induced Arrhythmia Risk Evaluation study-in England.

METHODS

Description of the processes followed when seeking research governance approval for the Drug-Induced Arrhythmia Risk Evaluation study-a case control study with annual follow-up of cases and controls over 5 years, set in the English National Health Service (NHS).

RESULTS

The authors describe wide variations in NHS research governance approval procedures in England.

CONCLUSION

NHS research governance procedures in England are impeding the process of epidemiological studies; there is the need for a centralised NHS R&D approval of studies, which is analogous to MREC for ethical approval.

Cardiological assessment of first-degree relatives in sudden arrhythmic death syndrome

4.1% of sudden cardiac deaths in the 16-64 age-group are unexplained. In this group, cardiac pathological findings are normal and toxicological tests are negative; termed sudden arrhythmic death syndrome (SADS). We searched for evidence of inherited cardiac disease in cases of SADS. Of 147 first-degree relatives of 32 people who died of SADS, 109 (74%) underwent cardiological assessment. Seven (22%) of the 32 families were diagnosed with inherited cardiac disease: four with long QT syndrome; one with non-structural cardiac electrophysiological disease; one with myotonic dystrophy; and one with hypertrophic cardiomyopathy. Families of people who die of SADS should be offered assessment in centres with experience of inherited cardiac disease.

PIP2 binding residues of Kir2.1 are common targets of mutations causing Andersen syndrome

BACKGROUND

Mutations in KCNJ2, the gene encoding the inward-rectifying K+ channel Kir2.1, cause the cardiac, skeletal muscle, and developmental phenotypes of Andersen-Tawil syndrome (ATS; also known as Andersen syndrome). Although pathogenic mechanisms have been proposed for select mutations, a common mechanism has not been identified.

METHODS

Seventeen probands presenting with symptoms characteristic of ATS were evaluated clinically and screened for mutations in KCNJ2. The results of mutation analysis were combined with those from previously studied subjects to assess the frequency with which KCNJ2 mutations cause ATS.

RESULTS

Mutations in KCNJ2 were discovered in nine probands. These included six novel mutations (D71N, T75R, G146D, R189I, G300D, and R312C) as well as previously reported mutations R67W and R218W. Six probands possessed mutations of residues implicated in binding membrane-associated phosphatidylinositol 4,5-bisphosphate (PIP2). In total, mutations in PIP(2)-related residues accounted for disease in 18 of 29 (62%) reported KCNJ2 -based probands with ATS. Also reported is that mutation R67W causes the full clinical triad in two unrelated males.

CONCLUSIONS

The novel mutations corresponding to residues involved in Kir2.1 channel-PIP2 interactions presented here as well as the overall frequency of mutations occurring in these residues indicate that defects in PIP2 binding constitute a major pathogenic mechanism of ATS. Furthermore, screening KCNJ2 in patients with the complex phenotypes of ATS was found to be invaluable in establishing or confirming a disease diagnosis as mutations in this gene can be identified in the majority of patients.

Simian immunodeficiency virus reverse transcriptase. Purification and partial characterization

Native reverse transcriptase from simian immunodeficiency virus was purified from virus with good recovery to near homogeneity. The optimum reaction conditions of the enzyme were determined with respect to divalent cations, pH and ionic strength. The enzyme was shown to possess both RNA-dependent and DNA-dependent DNA synthesis activity. In addition, we could demonstrate an associated RNase H activity. Employing novel assay conditions, activated DNA as a heteropolymeric substrate was used more efficiently than the homopolymeric substrate poly(rA).oligo(dT) which in turn was used twofold more effectively as the template primer than poly(dC).oligo(dG). Other homopolymeric substrates, including poly(rC).oligo(dG), were also tested but were found to be poorly used by the reverse transcriptase. The Miachaelis-Menten constants were determined for each of the four nucleotides needed to elongate a natural template primer. Simultaneously, using dideoxyadenosine triphosphate as nucleotide analogue, we could show that this compound acts as a competitive inhibitor with respect to dATP, whereas it acts as a non-competitive inhibitor with respect to the other nucleotides. Gel electrophoretic analysis showed the enzyme to consist of two polypeptides with apparent molecular masses of 64 and 48 kDa. Using activity gel electrophoresis, we were able to demonstrate that both subunits exhibit DNA synthesis activity.

Azidothymidine triphosphate is an inhibitor of both human immunodeficiency virus type 1 reverse transcriptase and DNA polymerase gamma

The reverse transcriptase from human immunodeficiency virus type 1 was purified from the virus to near homogeneity. The enzyme was shown to possess both RNA-dependent and DNA-dependent DNA-synthesizing activity. Activated DNA as a heteropolymeric substrate was used as efficiently as was the homopolymeric substrate poly(rA)-oligo(dT). The Michaelis-Menten constants were determined for each of the four nucleotides needed to elongate a natural template primer. Azidothymidine triphosphate, a well-known inhibitor of the enzyme, inhibited the enzyme competitively with respect to dTTP and noncompetitively with respect to the other nucleotides. Azidothymidine triphosphate acted as an efficient inhibitor of cellular DNA polymerase gamma, whereas other enzymes of eucaryotic DNA metabolism, namely, DNA polymerase alpha-primase and DNA polymerase beta, were not inhibited. This finding may explain why some acquired immunodeficiency syndrome patients suffer side effects during azidothymidine therapy.