Epidemiological, clinical and biochemical characterization of the p.(Ala359Asp) SMPD1 variant causing Niemann-Pick disease type B

Assessment of health state utilities associated with adult and pediatric acid sphingomyelinase deficiency (ASMD)

INTRODUCTION

Acid sphingomyelinase deficiency (ASMD) type B is a rare genetic disorder leading to enlargement of the spleen and liver, pulmonary dysfunction, and other symptoms. Cost-utility analyses are often conducted to quantify the value of new treatments, and these analyses require health state utilities. Therefore, the purpose of this study was to estimate utilities associated with varying levels of severity of adult and pediatric ASMD type B.

METHODS

Seven adult and seven child health state vignettes describing ASMD were developed based on published literature, clinical trial results, and interviews with clinicians, patients with ASMD, and parents of children with ASMD. The health states were valued in time trade-off interviews with adult general population respondents in the UK.

RESULTS

Interviews were completed with 202 participants (50.0% female; mean age = 41.3 years). The health state representing ASMD without impairment had the highest mean utility for both the adult and child health states (0.92/0.94), and severe ASMD had the lowest mean utility (0.33/0.45). Every child health state had a significantly greater utility than the corresponding adult health state. Differences between adult/child paired states ranged from 0.02 to 0.13. Subgroup analyses explored the impact of parenting status on valuation of child health states.

DISCUSSION

Greater severity of ASMD was associated with lower mean utility. Results have implications for valuation of pediatric health states. The resulting utilities may be useful in cost-utility modeling estimating the value of treatment for ASMD.

Consensus clinical management guidelines for acid sphingomyelinase deficiency (Niemann-Pick disease types A, B and A/B)

BACKGROUND

Acid Sphingomyelinase Deficiency (ASMD) is a rare autosomal recessive disorder caused by mutations in the SMPD1 gene. This rarity contributes to misdiagnosis, delayed diagnosis and barriers to good care. There are no published national or international consensus guidelines for the diagnosis and management of patients with ASMD. For these reasons, we have developed clinical guidelines that defines standard of care for ASMD patients.

METHODS

The information contained in these guidelines was obtained through a systematic literature review and the experiences of the authors in their care of patients with ASMD. We adopted the Appraisal of Guidelines for Research and Evaluation (AGREE II) system as method of choice for the guideline development process.

RESULTS

The clinical spectrum of ASMD, although a continuum, varies substantially with subtypes ranging from a fatal infantile neurovisceral disorder to an adult-onset chronic visceral disease. We produced 39 conclusive statements and scored them according to level of evidence, strengths of recommendations and expert opinions. In addition, these guidelines have identified knowledge gaps that must be filled by future research.

CONCLUSION

These guidelines can inform care providers, care funders, patients and their carers about best clinical practice and leads to a step change in the quality of care for patients with ASMD with or without enzyme replacement therapy (ERT).

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

Natural history and management of liver dysfunction in lysosomal storage disorders

Lysosomal storage disorders (LSD) are a rare group of genetic disorders. The major LSDs that cause liver dysfunction are disorders of sphingolipid lipid storage [Gaucher disease (GD) and Niemann-Pick disease] and lysosomal acid lipase deficiency [cholesteryl ester storage disease and Wolman disease (WD)]. These diseases can cause significant liver problems ranging from asymptomatic hepatomegaly to cirrhosis and portal hypertension. Abnormal storage cells initiate hepatic fibrosis in sphingolipid disorders. Dyslipidemia causes micronodular cirrhosis in lipid storage disorders. These disorders must be keenly differentiated from other chronic liver diseases and non-alcoholic steatohepatitis that affect children and young adults. GD, Niemann-Pick type C, and WD also cause neonatal cholestasis and infantile liver failure. Genotype and liver phenotype correlation is variable in these conditions. Patients with LSD may survive up to 4-5 decades except for those with neonatal onset disease. The diagnosis of all LSD is based on enzymatic activity, tissue histology, and genetic testing. Enzyme replacement is possible in GD and Niemann-Pick types A and B though there are major limitations in the outcome. Those that progress invariably require liver transplantation with variable outcomes. The prognosis of Niemann-Pick type C and WD is universally poor. Enzyme replacement therapy has a promising role in cholesteryl ester storage disease. This review attempts to outline the natural history of these disorders from a hepatologist’s perspective to increase awareness and facilitate better management of these rare disorders.

Interstitial lung disease in lysosomal storage disorders

Lysosomes are intracellular organelles that are responsible for degrading and recycling macromolecules. Lysosomal storage diseases (LSDs) are a group of inherited diseases caused by mutations affecting genes that encode the function of the lysosomal enzymes. Three LSDs are associated with lung involvement and/or interstitial lung disease (ILD): Gaucher disease (GD); Niemann-Pick disease, also known as acid sphingomyelinase deficiency (ASMD); and Fabry disease (FD). In GD and in ASMD, analysis of bronchoalveolar lavage fluid and lung biopsy can be informative, showing foamy cells. In GD, ILD is rare. Enzyme replacement therapy (ERT) has been available since 1991 and has greatly changed the natural history of GD, with pulmonary failure and death reported before the ERT era. In ASMD, ILD is frequent and is usually associated with spleen enlargement, low platelet cell count and low level of high-density lipoprotein-cholesterol. Results of ERT are promising regarding preliminary results of olipudase alfa in paediatric and adult ASMD populations. The most frequent respiratory manifestation in FD is COPD-like symptoms regardless of smoking habit and dyspnoea due to congestive heart failure. Early diagnosis of these three LSDs is crucial to prevent irreversible organ damage. Early initiation of ERT can, at least in part, prevent organ failure.

Niemann-Pick disease A or B in four pediatric patients and SMPD1 mutation carrier frequency in the Mexican population

INTRODUCTION AND OBJECTIVES

Niemann-Pick disease type A (NPD-A) and B (NPD-B) are lysosomal storage diseases with a birth prevalence of 0.4-0.6/100,000. They are caused by a deficiency in acid sphingomyelinase, an enzyme encoded by SMPD1. We analyzed the phenotype and genotype of four unrelated Mexican patients, one with NPD-A and three with NPD-B.

PATIENTS AND METHODS

Four female patients between 1 and 7 years of age were diagnosed with NPD-A or NPD-B by hepatosplenomegaly, among other clinical characteristics, and by determining the level of acid sphingomyelinase enzymatic activity and sequencing of the SMPD1 gene. Additionally, a 775bp amplicon of SMPD1 (from 11:6393835_6394609, including exons 5 and 6) was analyzed by capillary sequencing in a control group of 50 unrelated healthy Mexican Mestizos.

RESULTS

An infrequent variant (c.1343A>G p.Tyr448Cys) was observed in two patients. One is the first NPD-A homozygous patient reported with this variant and the other a compound heterozygous NPD-B patient with the c.1829_1831delGCC p.Arg610del variant. Another compound heterozygous patient had the c.1547A>G p.His516Arg variant (not previously described in affected individuals) along with the c.1805G>A p.Arg602His variant. A new c.1263+8C>T pathogenic variant was encountered in a homozygous state in a NPD-B patient. Among the healthy control individuals there was a heterozygous carrier for the c.1550A>T (rs142787001) pathogenic variant, but none with the known pathogenic variants in the 11:6393835_6394609 region of SMPD1.

CONCLUSIONS

The present study provides further NPD-A or B phenotype-genotype correlations. We detected a heterozygous carrier with a pathogenic variant in 1/50 healthy Mexican mestizos.

Biochemical and imaging parameters in acid sphingomyelinase deficiency: Potential utility as biomarkers

Acid Sphingomyelinase Deficiency (ASMD), or Niemann-Pick type A/B disease, is a rare lipid storage disorder leading to accumulation of sphingomyelin and its precursors primarily in macrophages. The disease has a broad phenotypic spectrum ranging from a fatal infantile form with severe neurological involvement (the infantile neurovisceral type) to a primarily visceral form with different degrees of pulmonary, liver, spleen and skeletal involvement (the chronic visceral type). With the upcoming possibility of treatment with enzyme replacement therapy, the need for biomarkers that predict or reflect disease progression has increased. Biomarkers should be validated for their use as surrogate markers of clinically relevant endpoints. In this review, clinically important endpoints as well as biochemical and imaging markers of ASMD are discussed and potential new biomarkers are identified. We suggest as the most promising biomarkers that may function as surrogate endpoints in the future: diffusion capacity measured by spirometry, spleen volume, platelet count, low-density lipoprotein cholesterol, liver fibrosis measured with a fibroscan, lysosphingomyelin and walked distance in six minutes. Currently, no biomarkers have been validated. Several plasma markers of lipid-laden cells, fibrosis or inflammation are of high potential as biomarkers and deserve further study. Based upon current guidelines for biomarkers, recommendations for the validation process are provided.

AISF update on the diagnosis and management of adult-onset lysosomal storage diseases with hepatic involvement

Lysosomal storage diseases (LSDs) are a heterogeneous group of inherited disorders caused by loss-of-function mutations in genes encoding for lysosomal enzymes/proteins. The consequence is a progressive accumulation of substrates in these intracellular organelles, resulting in cellular and tissue damage. The overall incidence is about 1/8000 live births, but is likely underestimated. LSDs are chronic progressive multi-systemic disorders, generally presenting with visceromegaly, and involvement of the central nervous system, eyes, the skeleton, and the respiratory and cardiovascular systems. The age at onset and phenotypic expression are highly variable, according to the specific enzymatic defect and tissues involved, the residual activity, and the disease-causing genotype. Enzyme-replacement therapies and substrate-reduction therapies have recently become available, leading to the improvement in symptoms, disease progression and quality of life of affected individuals. Liver involvement and hepatosplenomegaly are frequent features of LSDs and a hallmark of adult-onset forms, frequently leading to medical attention. LSDs should therefore be considered in the differential diagnosis of liver disease with organomegaly. The present document will provide a short overview of adult-onset LSDs with hepatic involvement, highlighting the specificities and systemic manifestations of the ones most frequently encountered in clinical practice, which may hint at the correct diagnosis and the appropriate treatment.

Mutational spectrum of SMPD1 gene in Pakistani Niemann-Pick disease patients

Objective:

Genetic variation analysis of rare autosomal recessive Niemann-Pick disease (NPD) Pakistani patients.

Methods:

We sequenced the SMPD1 gene including its all coding and flanking regions in seven unrelated sporadic patients suffering from Niemann-Pick disease through targeted exome sequencing. Genetic variants mapping and their protein predictions were evaluated using different bioinformatics tools and clinical phenotypes were correlated. The study was conducted from January 2018 to March 2019 at The Children’s Hospital Lahore.

Results:

We have mapped five different mutations in SMPD1 gene of enrolled patients with a novel homozygous missense variant (c.1718G>C) (p.Trp573Ser) in one patient. A missense mutation (c.1267C>T) (p.His423Tyr) has been identified in three unrelated patients. A nonsense mutation (c.1327C>T) (p.Arg443Term) and one missense mutation (c.1493G>A) (p.Arg498His) mapped in one patient each. A compound heterozygous mutation has been mapped in one patient (c.740G>A) (p.Gly247Asp); (c.1493G>A) (p.Arg498His). Pathogenic effect of novel variant has been predicted through in-silico analysis and has not been reported in general overall population in the globe.

Conclusion:

This is the first report of genetic demographic assessment of Niemann-Pick disease in Pakistan. The mapped mutations would be helpful to build a disease variants algorithm of Pakistani population. This will be used for determining disease clinical magnitude along with provision of genetic screening services in affected families.

Chronic visceral acid sphingomyelinase deficiency (Niemann-Pick disease type B) in 16 Polish patients: long-term follow-up

BACKGROUND

Acid sphingomyelinase deficiency (ASMD), due to mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene, is divided into infantile neurovisceral ASMD (Niemann-Pick type A), chronic neurovisceral ASMD (intermediate form, Niemann-Pick type A/B) and chronic visceral ASMD (Niemann-Pick type B). We conducted a long-term observational, single-center study including 16 patients with chronic visceral ASMD.

RESULTS

12 patients were diagnosed in childhood and 4 others in adulthood, the oldest at the age of 50. The mean time of follow-up was approximately 10 years (range: 6 months - 36 years). Splenomegaly was noted in all patients at diagnosis. Hepatomegaly was observed in 88% of patients. Moderately elevated (several-fold above the upper limit of normal values) serum transaminases were noted in 38% of patients. Cherry-red spots were found in five Gypsy children from one family and also in one adult Polish patient, a heterozygote for p.delR610 mutation. Dyslipidemia was noted in 50% of patients. Interstitial lung disease was diagnosed in 44% of patients. Plasmatic lysosphingomyelin (SPC) was elevated in all the patients except one with p.V36A homozygosity and a very mild phenotype also presenting with elevated plasmatic SPC-509 but normal chitotriosidase activity. The most common variant of SMPD1 gene was p.G166R. We found a previously unreported variant in exon 2 (c.491G > T, p.G164 V) in one patient.

CONCLUSIONS

Chronic visceral ASMD could constitute a slowly progressing disease with a relatively good outcome. The combined measurement of lysosphingomyelin (SPC) and lysospingomyelin-509 (SPC-509) is an essential method for the assessment of ASMD course.

Lysosomal and Mitochondrial Liaisons in Niemann-Pick Disease

Lysosomal storage disorders (LSD) are characterized by the accumulation of diverse lipid species in lysosomes. Niemann-Pick type A/B (NPA/B) and type C diseases Niemann-Pick type C (NPC) are progressive LSD caused by loss of function of distinct lysosomal-residing proteins, acid sphingomyelinase and NPC1, respectively. While the primary cause of these diseases differs, both share common biochemical features, including the accumulation of sphingolipids and cholesterol, predominantly in endolysosomes. Besides these alterations in lysosomal homeostasis and function due to accumulation of specific lipid species, the lysosomal functional defects can have far-reaching consequences, disrupting intracellular trafficking of sterols, lipids and calcium through membrane contact sites (MCS) of apposed compartments. Although MCS between endoplasmic reticulum and mitochondria have been well studied and characterized in different contexts, emerging evidence indicates that lysosomes also exhibit close proximity with mitochondria, which translates in their mutual functional regulation. Indeed, as best illustrated in NPC disease, alterations in the lysosomal-mitochondrial liaisons underlie the secondary accumulation of specific lipids, such as cholesterol in mitochondria, resulting in mitochondrial dysfunction and defective antioxidant defense, which contribute to disease progression. Thus, a better understanding of the lysosomal and mitochondrial interactions and trafficking may identify novel targets for the treatment of Niemann-Pick disease.

Disease manifestations and burden of illness in patients with acid sphingomyelinase deficiency (ASMD)

Acid sphingomyelinase deficiency (ASMD), a rare lysosomal storage disease, is an autosomal recessive genetic disorder caused by different SMPD1 mutations. Historically, ASMD has been classified as Niemann-Pick disease (NPD) types A (NPD A) and B (NPD B). NPD A is associated with a uniformly devastating disease course, with rapidly progressing psychomotor degeneration, leading to death typically by the age of 3 years, most often from respiratory failure. In contrast, the clinical phenotype and life expectancy of patients with NPD B may vary widely. Almost all patients have hepatosplenomegaly and an atherogenic lipid profile, and most patients have interstitial lung disease with progressive impairment of pulmonary function and hematologic abnormalities including cytopenias. Other common clinical manifestations include liver dysfunction, heart disease, skeletal abnormalities and growth delays. Some patients with ASMD who survive beyond early childhood have intermediate phenotypes (variant NPD B) characterized by combinations of non-neurologic and mild to severe neurologic symptoms. The physical and psychosocial burden of illness in patients with NPD B is substantial. Common symptoms include shortness of breath, joint or limb pain, abdominal pain, bleeding and bruising. The disease often leads to chronic fatigue, limited physical or social activity and difficulties in performing daily activities or work. Many patients die before or in early adulthood, often from pneumonia/respiratory failure or liver failure. Available treatments are limited to symptom management and supportive care. An enzyme replacement therapy currently in clinical development is expected to be the first treatment addressing the underlying pathology of the disease. Early diagnosis and appropriate management are essential for reducing the risk of complications. While knowledge about ASMD is evolving, more evidence about ASMD and the natural history across the disease spectrum is needed, to improve disease recognition, timely diagnosis and appropriate disease management.

Types A and B Niemann-Pick disease

The eponym Niemann-Pick disease (NPD) refers to a group of patients who present with varying degrees of lipid storage and foam cell infiltration in tissues, as well as overlapping clinical features including hepatosplenomegaly, pulmonary insufficiency and/or central nervous system (CNS) involvement. Due to the pioneering work of Roscoe Brady and co-workers, we now know that there are two distinct metabolic abnormalities that account for NPD. The first is due to the deficient activity of the enzyme acid sphingomyelinase (ASM; "types A & B" NPD), and the second is due to defective function in cholesterol transport ("type C" NPD). Herein only types A and B NPD will be discussed. Type A NPD patients exhibit hepatosplenomegaly in infancy and profound CNS involvement. They rarely survive beyond 2-3years of age. Type B patients also have hepatosplenomegaly and pathologic alterations of their lungs, but there are usually no CNS signs. The age of onset and rate of disease progression varies greatly among type B patients, and they frequently live into adulthood. Intermediate patients also have been reported with mild to moderate neurological findings. All patients with types A and B NPD have mutations in the gene encoding ASM (SMPD1), and thus the disease is more accurately referred to as ASM deficiency (ASMD). Herein we will review the clinical, pathological, biochemical, and genetic findings in types A and B NPD, and emphasize the seminal contributions of Dr. Brady to this disease. We will also discuss the current status of therapy for this disorder.

Structural and functional analysis of the ASM p.Ala359Asp mutant that causes acid sphingomyelinase deficiency

Niemann-Pick disease (NPD) type A and B are recessive hereditary disorders caused by deficiency in acid sphingomyelinase (ASM). The p.Ala359Asp mutation has been described in several patients but its functional and structural effects in the protein are unknown. In order to characterize this mutation, we modeled the three-dimensional ASM structure using the recent available crystal of the mammalian ASM as a template. We found that the p.Ala359Asp mutation is localized in the hydrophobic core and far from the sphingomyelin binding site. However, energy function calculations using statistical potentials indicate that the mutation causes a decrease in ASM stability. Therefore, we investigated the functional effect of the p.Ala359Asp mutation in ASM expression, secretion, localization and activity in human fibroblasts. We found a 3.8% residual ASM activity compared to the wild-type enzyme, without changes in the other parameters evaluated. These results support the hypothesis that the p.Ala359Asp mutation causes structural alterations in the hydrophobic environment where ASM is located, decreasing its enzymatic activity. A similar effect was observed in other previously described NPDB mutations located outside the active site of the enzyme. This work shows the first full size ASM mutant model describe at date, providing a complete analysis of the structural and functional effects of the p.Ala359Asp mutation over the stability and activity of the enzyme.