Faculty Bibliography

We present long-term pulmonary function test outcomes from an ongoing, open-label, multi-center, phase 3 extension study assessing the long-term safety and efficacy of elosulfase alfa enzyme replacement therapy (ERT) in patients with Morquio syndrome type A. In part 1 of the extension study, patients who were initially randomized to ERT in the original placebo-controlled 24-week study [1] remained on their regimen (2.0 mg/kg/week or every other week); placebo patients were re-randomized to one of the two treatment regimens. During part 2, all patients received ERT 2.0 mg/kg/week. Pulmonary function was evaluated as a secondary efficacy endpoint. Changes from the original 24-week study [1] baseline to 72 and 120 weeks are presented. In the 24-week study, non-statistical increases were seen in each dosing group for forced vital capacity (FVC) and maximum voluntary ventilation (MVV) versus placebo [1] and both endpoints continued to improve for the combined patient population during the extension study for up to 120 weeks. MVV increased from baseline by a mean (SE) of 1.78 (0.74) L/min by week 72 and 1.80 (1.04) L/min or 11.04 (4.55) % by week 120. FVC increased from baseline by a mean (SE) of 0.05 (0.01) L by week 72 and 0.08 (0.02) L or 8.6 (1.8) % by week 120. In contrast, matched untreated patients from the MorCAP natural history study [2] showed mean decreases in MVV and FVC over 2 years. In conclusion, long-term ERT causes sustained improvements in pulmonary function in patients with Morquio syndrome type A. References: 1. Hendriksz CJ, Burton B, Fleming TR, et al. J Inherit Metab Dis 2014;37:979-90. 2. Harmatz P, Mengel KE, Giugliani R, et al. Mol Genet Metab 2013;109:54-61. BioMarin Pharmaceutical Inc. sponsored this study.
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In patients with Late-Onset Pompe Disease (LOPD), progressive respiratory muscle involvement leads to reduced pulmonary function, with respiratory failure the most common cause of mortality. Early disease manifestations include sleep-disordered breathing, which can be treated with non-invasive ventilation; however, progressive diurnal deficits can require invasive ventilation. To determine if pulmonary function tests (PFTs) predict the thresholds for ventilation and wheelchair use, a systematic literature review identified cross-sectional clinical patient data (N = 174) that was classified into ventilation and wheelchair cohorts. PFTs included maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), forced vital capacity (FVC), and vital capacity (VC), with vital capacities measured in the upright (-U) and supine (-S) positions. Receiver operating characteristic (ROC) curves were used to calculate cut-points (CP) and area under the curve (AUC). For all ventilation and mobility thresholds tested, ROC analyses demonstrated AUC values from 86-89% for MIP, 72-96% for MEP, and 74-96% for all vital capacity metrics. Thus, PFTs are useful in predicting the thresholds for nighttime ventilation, daytime ventilation, and wheelchair use, with MIP and VC-U having both high AUC values and consistency. The PFT mobility CPs were low (MIP CP = 0.9 kPa, MEP, CP = 2.6 kPa, VC-U CP = 19% predicted), suggesting an endurance component associated with wheelchair use.

RATIONALE: Obesity is characterized by increased systemic and pulmonary blood volumes (pulmonary vascular congestion). Concomitant abnormal alveolar membrane diffusion suggests subclinical interstitial edema. In this setting, functional abnormalities should encompass the entire distal lung including the airways. OBJECTIVES: We hypothesize that in obesity: 1) pulmonary vascular congestion will affect the distal lung unit with concordant alveolar membrane and distal airway abnormalities; and 2) the degree of pulmonary congestion and membrane dysfunction will relate to the cardiac response. METHODS: 54 non-smoking obese subjects underwent spirometry, impulse oscillometry (IOS), diffusion capacity (DLCO) with partition into membrane diffusion (DM) and capillary blood volume (VC), and cardiac MRI (n = 24). Alveolar-capillary membrane efficiency was assessed by calculation of DM/VC. MEASUREMENTS AND MAIN RESULTS: Mean age was 45+/-12 years; mean BMI was 44.8+/-7 kg/m2. Vital capacity was 88+/-13% predicted with reduction in functional residual capacity (58+/-12% predicted). Despite normal DLCO (98+/-18% predicted), VC was elevated (135+/-31% predicted) while DM averaged 94+/-22% predicted. DM/VC varied from 0.4 to 1.4 with high values reflecting recruitment of alveolar membrane and low values indicating alveolar membrane dysfunction. The most abnormal IOS (R5 and X5) occurred in subjects with lowest DM/VC (r2 = 0.31, p<0.001; r2 = 0.34, p<0.001). Cardiac output and index (cardiac output / body surface area) were directly related to DM/VC (r2 = 0.41, p<0.001; r2 = 0.19, p = 0.03). Subjects with lower DM/VC demonstrated a cardiac output that remained in the normal range despite presence of obesity. CONCLUSIONS: Global dysfunction of the distal lung (alveolar membrane and distal airway) is associated with pulmonary vascular congestion and failure to achieve the high output state of obesity. Pulmonary vascular congestion and consequent fluid transudation and/or alterations in the structure of the alveolar capillary membrane may be considered often unrecognized causes of airway dysfunction in obesity.

We agree that the "holy grail" of pulmonary physiologists is a test that detects early chronic airway disease. While Dr. Enright remains "cautiously optimistic" that FOT can serve this purpose, there are sufficient data to mitigate his caution.