Methionine supplementation for multi-organ dysfunction in MetRS-related pulmonary alveolar proteinosis.

INTRODUCTION: Pulmonary alveolar proteinosis related to mutations in the methionine tRNA synthetase (MARS1) gene is a severe, early-onset disease that results in death before the age of 2 years in one-third of patients. It is associated with a liver disease, growth failure and systemic inflammation. As methionine supplementation in yeast models restored normal enzymatic activity of the synthetase, we studied the tolerance, safety and efficacy of daily oral methionine supplementation in patients with severe and early disease. METHODS: Four patients received methionine supplementation and were followed for respiratory, hepatic, growth and inflammation-related outcomes. Their course was compared to those of historical controls. Reactive oxygen species production by patient monocytes before and after methionine supplementation was also studied. RESULTS: Methionine supplementation was associated with respiratory improvement, clearance of the extracellular lipoproteinaceous material and discontinuation of whole-lung lavage in all patients. The three patients who required oxygen or noninvasive ventilation could be weaned off within 60 days. In addition, liver dysfunction, inflammation and growth delay improved or resolved. At a cellular level, methionine supplementation normalised the production of reactive oxygen species by peripheral monocytes. CONCLUSION: Methionine supplementation was associated with important improvements in children with pulmonary alveolar proteinosis related to mutations in the MARS1 gene. This study paves the way for similar strategies for other tRNA synthetase deficiencies.

Heterogeneity of lung disease associated with NK2 homeobox 1 mutations.

We retrospectively studied the clinical presentation, treatment modalities and outcome in 16 patients with heterozygous NKX2-1 mutation associated with chronic lung disease. Twelve different NKX2-1 mutations, including 4 novel mutations, were identified in the 16 patients. Nine patients presented with brain-lung-thyroid syndrome, 3 had neurological and lung symptoms and 4 had only pulmonary symptoms. Ten patients had neonatal respiratory distress, and 6 of them developed infiltrative lung disease (ILD). The other patients were diagnosed with ILD in childhood (n = 3) or in adulthood (n = 3). The median age at diagnosis was 36 months (IQ 3.5-95). Patient testing included HRCT (n = 13), BALF analysis (n = 6), lung biopsies (n = 3) and lung function tests (n = 6). Six patients required supplemental oxygen support with a median duration of 18 months (IQ 2.5-29). All symptomatic ILD patients (n = 12) benefited from a treatment consisting of steroids, azithromycin (n = 9), and/or hydroxychloroquine (n = 4). The median follow-up was 36 months (IQ 24-71.5). One patient died of respiratory failure at 18 months and another is waiting for lung transplantation. In summary, the initial diagnosis was based on clinical presentation and radiological features, but the presentation was heterogeneous. Definitive diagnosis required genetic analysis, which should be performed, even in absence of neurological or thyroid symptoms.

Hepatic Steatosis Accompanies Pulmonary Alveolar Proteinosis.

Maintenance of tissue-specific organ lipid compositions characterizes mammalian lipid homeostasis. The lungs and liver synthesize mixed phosphatidylcholine (PC) molecular species that are subsequently tailored for function. The lungs progressively enrich disaturated PC directed to lamellar body surfactant stores before secretion. The liver accumulates polyunsaturated PC directed to very-low-density lipoprotein assembly and secretion, or to triglyceride stores. In each tissue, selective PC species enrichment mechanisms lie at the heart of effective homeostasis. We tested for potential coordination between these spatially separated but possibly complementary phenomena under a major derangement of lung PC metabolism, pulmonary alveolar proteinosis (PAP), which overwhelms homeostasis and leads to excessive surfactant accumulation. Using static and dynamic lipidomics techniques, we compared (1) tissue PC compositions and contents, and (2) in lungs, the absolute rates of synthesis in both control mice and the granulocyte-macrophage colony-stimulating factor knockout model of PAP. Significant disaturated PC accumulation in bronchoalveolar lavage fluid, alveolar macrophage, and lavaged lung tissue occurred alongside increased PC synthesis, consistent with reported defects in alveolar macrophage surfactant turnover. However, microscopy using oil red O staining, coherent anti-Stokes Raman scattering, second harmonic generation, and transmission electron microscopy also revealed neutral-lipid droplet accumulations in alveolar lipofibroblasts of granular macrophage colony-stimulating factor knockout animals, suggesting that lipid homeostasis deficits extend beyond alveolar macrophages. PAP plasma PC composition was significantly polyunsaturated fatty acid enriched, but the content was unchanged and hepatic polyunsaturated fatty acid-enriched PC content increased by 50% with an accompanying micro/macrovesicular steatosis and a fibrotic damage pattern consistent with nonalcoholic fatty liver disease. These data suggest a hepatopulmonary axis of PC metabolism coordination, with wider implications for understanding and managing lipid pathologies in which compromise of one organ has unexpected consequences for another.

Lysinuric protein intolerance: reviewing concepts on a multisystem disease.

Lysinuric protein intolerance (LPI) is an inherited aminoaciduria caused by defective cationic amino acid transport at the basolateral membrane of epithelial cells in intestine and kidney. LPI is caused by mutations in the SLC7A7 gene, which encodes the y(+)LAT-1 protein, the catalytic light chain subunit of a complex belonging to the heterodimeric amino acid transporter family. LPI was initially described in Finland, but has worldwide distribution. Typically, symptoms begin after weaning with refusal of feeding, vomiting, and consequent failure to thrive. Hepatosplenomegaly, hematological anomalies, neurological involvement, including hyperammonemic coma are recurrent clinical features. Two major complications, pulmonary alveolar proteinosis and renal disease are increasingly observed in LPI patients. There is extreme variability in the clinical presentation even within individual families, frequently leading to misdiagnosis or delayed diagnosis. This condition is diagnosed by urine amino acids, showing markedly elevated excretion of lysine and other dibasic amino acids despite low plasma levels of lysine, ornithine, and arginine. The biochemical diagnosis can be uncertain, requiring confirmation by DNA testing. So far, approximately 50 different mutations have been identified in the SLC7A7 gene in a group of 142 patients from 110 independent families. No genotype-phenotype correlation could be established. Therapy requires a low protein diet, low-dose citrulline supplementation, nitrogen-scavenging compounds to prevent hyperammonemia, lysine, and carnitine supplements. Supportive therapy is available for most complications with bronchoalveolar lavage being necessary for alveolar proteinosis.

Nonspecific interstitial pneumonia, alveolar proteinosis, and abnormal proprotein trafficking resulting from a spontaneous mutation in the surfactant protein C gene.

Human surfactant protein C (hSP-C(1-197)) is synthesized as a 197 amino acid proprotein and cleaved to a mature 3.7 kD form. Although interstitial lung disease in patients with mutations of the hSP-C gene is becoming increasingly recognized, the mechanisms linking molecular events with clinical pathogenesis are not fully defined. We describe a full-term infant with respiratory insufficiency associated with a spontaneous heterozygous mutation resulting in a substitution of lysine for glutamic acid at position 66 (= E66K) of the proximal hSP-C COOH flanking propeptide. Lung histology and biochemical studies of the index patient (hSP-C(E66K)) revealed nonspecific interstitial pneumonia, increased alveolar total phospholipid lacking phosphatidylglycerol, and increased surfactant protein A. Localization of proSP-C from lung sections prepared from this patient using immunofluorescence and immunogold electron microscopy revealed abnormal proSP-C staining in endosomal-like vesicles of type II cells distinct from SP-B. To evaluate the effect of the E66K substitution on intracellular trafficking of proSP-C, fusion proteins consisting of enhanced green fluorescent protein (EGFP) and hSP-C(1-197) (wild type) or mutant hSP-C(E66K) were generated and transfected into A549 cells. EGFP/hSP-C(1-197) was expressed within CD-63-positive, EEA-1-negative vesicles, whereas EGFP/hSP-C(E66K) localized to EEA-1 positive vesicles. The E66K substitution is representative of a new class of SP-C mutation associated with interstitial lung disease that is diverted from the normal biosynthetic pathway. We propose that, similar to other storage disorders, lung injury results from induction of a toxic gain of function induced by the mutant product that is subject to genetic modifiers and environmental influences.