Farber disease (FD) is a debilitating lysosomal storage disorder (LSD) caused by a deficiency of acid ceramidase (ACDase) activity due to mutations in the gene ASAH1. Patients with ACDase deficiency may develop a spectrum of clinical phenotypes. Severe cases of FD are frequently associated with neurological involvement, failure to thrive, and respiratory complications. Mice homozygous ( Asah1) for an orthologous patient mutation in Asah1 recapitulate human FD. In this study, we show significant impairment in lung function, including low compliance and increased airway resistance in a mouse model of ACDase deficiency. Impaired lung mechanics in Farber mice resulted in decreased blood oxygenation and increased red blood cell production. Inflammatory cells were recruited to both perivascular and peribronchial areas of the lung. We observed large vacuolated foamy histiocytes that were full of storage material. An increase in vascular permeability led to protein leakage, edema, and impacted surfactant homeostasis in the lungs of Asah1 mice. Bronchial alveolar lavage fluid (BALF) extraction and analysis revealed accumulation of a highly turbid lipoprotein-like substance that was composed in part of surfactants, phospholipids, and ceramides. The phospholipid composition of BALF from Asah1 mice was severely altered, with an increase in both phosphatidylethanolamine (PE) and sphingomyelin (SM). Ceramides were also found at significantly higher levels in both BALF and lung tissue from Asah1 mice when compared with levels from wild-type animals. We demonstrate that a deficiency in ACDase leads to sphingolipid and phospholipid imbalance, chronic lung injury caused by significant inflammation, and increased vascular permeability, leading to impaired lung function.

This study is registered under the identifier NCT04832841 on ClinicalTrials.gov.

Ornithine transcarbamylase (OTC) deficiency is an X-linked disorder that causes recurrent and life-threatening episodes of hyperammonemia. The clinical picture in heterozygous females is highly diverse and derives from the genotype and the degree of inactivation of the mutated X chromosome in hepatocytes. Here, we describe molecular genetic, biochemical, and histopathological findings in the livers explanted from two female patients with late-onset OTC deficiency. Analysis of X-inactivation ratios by DNA methylation-based assays showed remarkable intra-organ variation ranging from 46:54 to 82:18 (average 70:30, n = 37), in favor of the active X chromosome carrying the mutation c.583G>C (p.G195R), in the first patient and from 75:25 to 90:10 (average 82:18, n = 20) in favor of the active X chromosome carrying the splicing mutation c.663+1G>A in the second patient. The X-inactivation ratios in liver samples correlated highly with the proportions of OTC-positive hepatocytes calculated from high-resolution image analyses of the immunohistochemically detected OTC in frozen sections that was performed on total area > 5 cm. X-inactivation ratios in blood in both female patients corresponded to the lower limit of the liver values. Our data indicate that the proportion of about 20-30% of hepatocytes expressing the functional OTC protein is not sufficient to maintain metabolic stability. X-inactivation ratios assessed in liver biopsies taken from heterozygous females with X-linked disorders should not be considered representative of the whole liver.

Farber disease (FD) is a debilitating lysosomal storage disorder characterized by severe inflammation and neurodegeneration. FD is caused by mutations in the ASAH1 gene, resulting in deficient acid ceramidase (ACDase) activity. Patients with ACDase deficiency exhibit a broad clinical spectrum. In classic cases, patients develop hepatosplenomegaly, nervous system involvement, and childhood mortality. Ocular manifestations include decreased vision, a grayish appearance to the retina with a cherry red spot, and nystagmus. That said, the full effect of ACDase deficiency on the visual system has not been studied in detail. We previously developed a mouse model that is orthologous for a known patient mutation in Asah1 that recapitulates human FD. Herein, we report evidence of a severe ocular pathology in Asah1 P361R/P361R mice. Asah1 P361R/P361R mice exhibit progressive retinal and optic nerve pathology. Through noninvasive ocular imaging and histopathological analyses of these Asah1 P361R/ P361R animals, we revealed progressive inflammation, the presence of retinal dysplasia, and significant storage pathology in various cell types in both the retina and optic nerves. Lipidomic analyses of retinal tissues revealed an abnormal accumulation of ceramides and other sphingolipids. Electroretinograms and behavioral tests showed decreased retinal and visual responses. Taken together, these data suggest that ACDase deficiency leads to sphingolipid imbalance, inflammation, dysmorphic retinal and optic nerve pathology, and severe visual impairment. (Am J Pathol 2019, 189: 320e338; https://doi.