Acid Ceramidase Deficiency: Bridging Gaps between Clinical Presentation, Mouse Models, and Future Therapeutic Interventions

Farber disease (FD) and spinal muscular atrophy with progressive myoclonic epilepsy (SMA-PME) are ultra-rare, autosomal-recessive, acid ceramidase (ACDase) deficiency disorders caused by ASAH1 gene mutations. Currently, 73 different mutations in the ASAH1 gene have been described in humans. These mutations lead to reduced ACDase activity and ceramide (Cer) accumulation in many tissues. Presenting as divergent clinical phenotypes, the symptoms of FD vary depending on central nervous system (CNS) involvement and severity. Classic signs of FD include, but are not limited to, a hoarse voice, distended joints, and lipogranulomas found subcutaneously and in other tissues. Patients with SMA-PME lack the most prominent clinical signs seen in FD. Instead, they demonstrate muscle weakness, tremors, and myoclonic epilepsy. Several ACDase-deficient mouse models have been developed to help elucidate the complex consequences of Cer accumulation. In this review, we compare clinical reports on FD patients and experimental descriptions of ACDase-deficient mouse models. We also discuss clinical presentations, potential therapeutic strategies, and future directions for the study of FD and SMA-PME.

Acid Ceramidase Depletion Impairs Neuronal Survival and Induces Morphological Defects in Neurites Associated with Altered Gene Transcription and Sphingolipid Content

The ASAH1 gene encodes acid ceramidase (AC), an enzyme that is implicated in the metabolism of ceramide (Cer). Mutations in the ASAH1 gene cause two different disorders, Farber disease (FD), a rare lysosomal storage disorder, and a rare form of spinal muscular atrophy combined with progressive myoclonic epilepsy (SMA-PME). In the absence of human in vitro neuronal disease models and to gain mechanistic insights into pathological effects of ASAH1 deficiency, we established and characterized a stable ASAH1 knockdown (ASAH1KD) SH-SY5Y cell line. ASAH1KD cells displayed reduced proliferation due to elevated apoptosis and G1/S cell cycle arrest. Distribution of LAMP1-positive lysosomes towards the cell periphery and significantly shortened and less branched neurites upon differentiation, implicate AC for lysosome positioning and neuronal development, respectively. Lipidomic analysis revealed changes in the intracellular levels of distinct sphingolipid species, importantly without Cer accumulation, in line with altered gene transcription within the sphingolipid pathway. Additionally, the transcript levels for Rho GTPases (RhoA, Rac1, and Cdc42), which are key regulators of axonal orientation, neurite branching and lysosome positioning were found to be dysregulated. This study shows the critical role of AC in neurons and suggests how AC depletion leads to defects seen in neuropathology of SMA-PME and FD.

Genetic, clinical and biochemical characterization of a large cohort of patients with hyaline fibromatosis syndrome

BACKGROUND

Hyaline fibromatosis syndrome (HFS) is a rare clinical condition in which bi-allelic variants in ANTXR2 are associated with extracellular hyaline deposits. It manifests as multiple skin nodules, patchy hyperpigmentation, joint contractures and severe pain with movement. HFS shows some clinical overlap to Farber disease (FD), a recessive lysosomal storage disorder.

RESULTS

We here present the largest cohort of independent, genetically confirmed HFS cases reported to date: in 19 unrelated index patients, we identified ten distinct homozygous ANTXR2 mutations, three of which are novel frame-shift variants. The associated clinical data are consistent with the previous hypothesis of non-truncating variants in the terminal exons 13-17 to confer rather mild phenotypes. The novel observation of gender-dependent disease manifestation in our cohort received support from a meta-analysis of all previously published cases. Untargeted blood-based metabolomics revealed patient samples to be biochemically distinct from control samples. Numerous potential HFS biomarker metabolites could thus be identified. We also found metabolomics profiles of HFS patients to highly overlap with those from FD patients.

CONCLUSIONS

Our study extends the mutational spectrum for HFS, suggests gender-dependency of manifestation, and provides pilot metabolomics data for biomarker identification and a better pathomechanistic understanding of the disorder.

Allogeneic hematopoietic cell transplantation in Farber disease

BACKGROUND

Farber disease (FD) is a rare, lysosomal storage disorder caused by deficient acid ceramidase activity. FD has long been considered a fatal disorder with death in the first three decades of life resulting either from respiratory insufficiency as a consequence of airway involvement or from progressive neurodegeneration because of nervous system involvement. Peripheral symptoms associated with FD, including inflammatory joint disease, have been described to improve relatively rapidly after hematopoietic cell transplantation (HCT).

AIMS

To evaluate the disease-specific status and limitations in the long-term follow-up after HCT, investigate genotype/phenotype correlations and the benefit of allogeneic HCT in FD patients with nervous system involvement.

PATIENTS AND METHODS

Transplant- and disease-related information of ten FD patients was obtained by using a questionnaire, physicians' letters and additional telephone surveys. ASAH1 gene mutations were identified to search for genotype/phenotype correlations.

RESULTS

After mainly busulfan-based preparative regimens, all patients engrafted with one late graft loss. The inflammatory symptoms resolved completely in all patients. Abnormal neurologic findings were present pre-transplant in 4/10 patients, post-transplant in 6/10 patients. Mutational analyses revealed new mutations in the ASAH1 gene and a broad diversity of phenotypes without a genotype/phenotype correlation. With a median follow-up of 10.4 years, overall survival was 80% with two transplant-related deaths.

CONCLUSION

Allogeneic HCT leads to complete and persistent resolution of the inflammatory aspects in FD patients. It appears to have no beneficial effect on progression of nervous system involvement. New mutations in the acid ceramidase gene were identified. A genotype/phenotype correlation could not be established.

Molecular basis of acid ceramidase deficiency in a neonatal form of Farber disease: identification of the first large deletion in ASAH1 gene

Farber disease, also known as Farber's lipogranulomatosis, is a clinically heterogeneous autosomal recessive disease caused by mutations in the ASAH1 gene. This gene codes for acid ceramidase, a lysosomal heterodimeric enzyme that hydrolyzes ceramide into sphingosine and fatty acid. To date, less than 25 distinct mutations have been identified in Farber patients, but no large deletions have yet been reported. In this work, cultured fibroblasts from a Farber patient with the rare neonatal form of Farber disease were studied to elucidate the molecular basis of this extremely severe phenotype. Direct sequencing of ASAH1 genomic DNA revealed the causative heterozygous mutation in the donor splice site consensus sequence of intron 11, g.24491A > G (c.917 + 4A > G), that resulted in the absence of detectable mRNA. Subsequent analysis of ASAH1 mRNA showed total skipping of exons 3 to 5. Long-range PCR and sequencing led to the identification of a gross deletion of ASAH1 gene, g.8728_18197del (c.126-3941_382 + 1358del) predicting the synthesis of a truncated polypeptide, p.Tyr42_Leu127delinsArgfs*10. Accordingly, no molecular forms corresponding to precursor or proteolytically processed mature protein were observed. These findings indicate that any functionally active acid ceramidase is absent in patient cells, underscoring the severity of the clinical phenotype. Molecular findings in the non-consanguineous parents confirmed the compound heterozygous ASAH1 genotype identified in this Farber case. This work unravels for the first time the mutations underlying the neonatal form of Farber disease and represents the first report of a large deletion identified in the ASAH1 gene. Screening for gross deletions in other patients in whom the mutation present in the second allele had not yet been identified is required to elucidate further its overall contribution for the molecular pathogenesis of this devastating disease.

Novel biochemical abnormalities and genotype in Farber disease

Farber disease caused by acid ceramidase deficiency is characterised by a triad of painful and swollen joints, subcutaneous nodules, and laryngeal involvement. A one year old female with overlapping features of the classical and type 5 variants is reported. Sialuria and elevated plasma chitotriosidase were unusual findings. A novel mutation of the ASAH 1 gene was detected from DNA extracted from the umbilical stump.

Farber lipogranulomatosis type 1--late presentation and early death in a Croatian boy with a novel homozygous ASAH1 mutation

BACKGROUND

We report a boy with an unusually late presentation of Farber lipogranulomatosis type l.

CASE STUDY

The first symptoms appeared at the end of the first year of life in the form of joint swelling; other symptoms such as cherry-red spot, hoarseness, subcutaneous nodules appeared much later. The history of the disease, from the first symptoms till his early death, lasted 26.5 months. The neuronal dysfunction accompanied by the rapid neurological deterioration with seizures and myoclonias, rather than the general dystrophy, seemed to limit the duration of disease in our patient and provoked his early death. Diagnosis was confirmed by analysis of ceramide metabolism in cultured fibroblasts and of the ASAH1 gene, which indicated homozygosity for a novel point mutation.

CONCLUSION

The deficient activity of acid ceramidase correlated well with poor prognosis of the disease in our boy, in contrast to late appearance of dermal nodules and the subsequent severe clinical course with fatal outcome. Farber lipogranulomatosis should be suspected in children with joint swelling as the first and only symptom of disease. In order to advance our knowledge towards establishing genotype-phenotype correlations in Farber's disease, detailed analysis of the ASAH1 gene is needed.

In vivo delivery of human acid ceramidase via cord blood transplantation and direct injection of lentivirus as novel treatment approaches for Farber disease

Farber disease is a rare lysosomal storage disorder (LSD) caused by a deficiency of acid ceramidase (AC) activity and subsequent accumulation of ceramide. Currently, there is no treatment for Farber disease beyond palliative care and most patients succumb to the disorder at a very young age. Previously, our group showed that gene therapy using oncoretroviral vectors (RV) could restore enzyme activity in Farber patient cells. The studies described here employ novel RV and lentiviral (LV) vectors that engineer co-expression of AC and a cell surface marking transgene product, human CD25 (huCD25). Transduction of Farber patient fibroblasts and B cells with these vectors resulted in overexpression of AC and led to a 90% and 50% reduction in the accumulation of ceramide, respectively. Vectors were also evaluated in human hematopoietic stem/progenitor cells (HSPCs) and by direct in vivo delivery in mouse models. In a xenotransplantation model using NOD/SCID mice, we found that transduced CD34(+) cells could repopulate irradiated recipient animals, as measured by CD25 expression. When virus was injected intravenously into mice, soluble CD25 was detected in the plasma and increased AC activity was present in the liver up to 14 weeks post-injection. These findings suggest that vector and transgene expression can persist long-term and offer the potential of a lasting cure. To our knowledge, this is the first report of in vivo testing of direct gene therapy strategies for Farber disease.