Prenatal diagnosis of Niemann-Pick diseases types A, B and C

Expert opinion on patient journey, diagnosis and clinical monitoring in acid sphingomyelinase deficiency in Turkey: a pediatric metabolic disease specialist's perspective

This review by a panel of pediatric metabolic disease specialists aimed to provide a practical and implementable guidance document to assist clinicians in best clinical practice in terms of recognition, diagnosis and management of patients with acid sphingomyelinase deficiency (ASMD). The participating experts consider the clinical suspicion of ASMD by the physician to be of utmost importance in the prevention of diagnostic delay and strongly suggest the use of a diagnostic algorithm including/starting with dried blood spots assay in the timely diagnosis of ASMD in patients presenting with hepatosplenomegaly and a need for increased awareness among physicians in this regard to consider ASMD in the differential diagnosis. In anticipation of the introduction of enzyme replacement therapy, raising awareness of the disease among physicians to prevent diagnostic delay and further investigation addressing natural history of ASMD across the disease spectrum, potential presenting characteristics with a high index of suspicion, as well as biomarkers and genotype-phenotype correlations suggestive of poor prognosis seem important in terms of implementation of best practice patterns.

Acid Sphingomyelinase Deficiency: Sharing Experience of Disease Monitoring and Severity in France

Acid sphingomyelinase deficiency (ASMD) is a rare inherited lipid storage disorder caused by a deficiency in lysosomal enzyme acid sphingomyelinase which results in the accumulation of sphingomyelin, predominantly within cells of the reticuloendothelial system located in numerous organs, such as the liver, spleen, lungs, and central nervous system. Although all patients with ASMD share the same basic metabolic defect, a wide spectrum of clinical presentations and outcomes are observed, contributing to treatment challenges. While infantile neurovisceral ASMD (also known as Niemann-Pick disease type A) is rapidly progressive and fatal in early childhood, and the more slowly progressive chronic neurovisceral (type A/B) and chronic visceral (type B) forms have varying clinical phenotypes and life expectancy. The prognosis of visceral ASMD is mainly determined by the association of hepatosplenomegaly with secondary thrombocytopenia and lung disease. Early diagnosis and appropriate management are essential to reduce the risk of complications and mortality. The accessibility of the new enzyme replacement therapy olipudase alfa, a recombinant human ASM, has been expedited for clinical use based on positive clinical data in children and adult patients, such as improved respiratory status and reduced spleen volume. The aim of this article is to share the authors experience on monitoring ASMD patients and stratifying the severity of the disease to aid in care decisions.

First Prenatal Diagnosis of a Niemann-Pick Disease Type C2 Revealed by a Cystic Hygroma: A Case Report and Review of the Literature

BACKGROUND

The importance of fetal nuchal translucency was highlighted in the early 1990s as a useful first-trimester marker to identify fetal chromosomal abnormalities. Here, we report the prenatal diagnosis of a fetus with Niemann-Pick disease type C initially identified by first-trimester ultrasonographic markers and eventually confirmed by extensive genetic evaluation.

CASE PRESENTATION

The fetus of a 30-year-old woman exhibited a cystic hygroma in the first trimester of pregnancy. The woman underwent chorionic villus sampling with extensive genetic investigations to identify the genetic cause of the ultrasonographic findings. Owing to normal karyotype results, further evaluation of 1,024 genes underlying structural abnormalities was performed. This test identified a homozygous mutation of the NPC2 gene (OMIM 601015), which has been reported to be pathogenic and responsible for Niemann-Pick disease type C2 (NPD-C2). Genetic evaluation of the parents found them to be carriers. Considering the poor prognosis, the parents decided to terminate the pregnancy. Ultrasonographic screening during the subsequent pregnancy showed normal findings; however, molecular testing for the previous familial mutation c.441 + 1G>A identified the fetus as homozygous for this mutation. Therefore, the parent chose to terminate the subsequent pregnancy as well.

CONCLUSION

We report the first prenatal diagnosis of NPD-C2 based on a cystic hygroma found during the first trimester of pregnancy as the sole indicator.

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.

[Acid sphingomyelinase deficiency (Niemann-Pick disease type B) in adulthood: A retrospective multicentric study of 28 adult cases]

INTRODUCTION

Acid sphingomyelinase deficiency (ASMD) is an autosomal recessive disease with a clinical spectrum ranging from a neurovisceral infantile form (Niemann-Pick disease type A) to a chronic visceral form also encountered in adults (Niemann-Pick disease type B, NP-B).

METHODS

Retrospective multicentric analysis of French adult patients with ASMD over the period 1985-March 2015. Clinical, biological, and imaging data were analyzed.

RESULTS

Twenty-eight patients (19 males, 9 females) were analyzed. Diagnosis was made before the age of 10 years in 16 cases. Main symptoms at diagnosis were spleen/liver enlargement and interstitial lung disease. Biological abnormalities included: thrombocytopenia (platelet count <150 000/mm³) in 24 cases including 4 patients with platelet count <60 000/mm³, constantly low high-density lipoprotein (HDL) cholesterol, polyclonal hypergammaglobulinemia (n=6), monoclonal gammopathy of unknown significance (n=5), normal prothrombin level discordant with low factor V (n=5), elevated chitotriosidase level (n=11). The diagnosis was confirmed in all cases by deficient acid sphingomyelinase enzyme activity. SMPD1 gene sequencing was performed in 25 cases. The frequent p.R610del mutation was largely predominant, constituting 62% of the non-related alleles. During the follow-up period, three patients died before 50 years of age from cirrhosis, heart failure and lung insufficiency, respectively.

CONCLUSION

ASMD in adulthood (NP-B) associates spleen/liver enlargement and interstitial lung disease. Early diagnosis and appropriate management are essential for reducing the risk of complications, improving quality of life, and avoiding inappropriate procedures such as splenectomy. To date, only symptomatic therapy is available. A phase 2/3 therapeutic trial with IV infusion of recombinant enzyme is on-going.

In Utero Diagnosis of Niemann-Pick Type C in the Absence of Family History

Niemann-Pick type C (NPC) disease is a recessive disorder that results in unesterified cholesterol accumulating in the lysosomal and late endosomal system. It is caused by mutations in NPC1 or NPC2 genes and leads to systemic and neurodegenerative symptoms. Few cases of prenatal presentation of NPC have been reported and only two cases in the absence of previous family history, indicating the diagnosis is particularly difficult in such a situation. We report a prenatal diagnosis of NPC in a couple without family history. An ultrasound screening at 22 weeks of gestation (WG) detected fetal ascites and hepatomegaly, which were still present at 25, 27, and 29 WG, and a splenomegaly progressively appeared. No placentomegaly or other signs of hydrops fetalis were observed. The diagnostic of NPC was prenatally confirmed by a filipin test and NPC1 sequencing and multiplex ligation-dependent probe amplification assay which revealed a maternal missense mutation (c.2608T>C; p.Ser870Pro) and a paternal deletion of exons 5 to 25. This additional prenatal case of NPC suggests that even in the absence of family history, fetal ascites associated with splenomegaly but no hydrops should nonetheless arouse suspicion concerning this disease as a possible diagnosis.

Recommendations for the diagnosis and management of Niemann-Pick disease type C: an update

Niemann-Pick disease type C (NP-C) is a rare inherited neurovisceral disease caused by mutations in either the NPC1 (in 95% of cases) or the NPC2 gene (in around 5% of cases), which lead to impaired intracellular lipid trafficking and accumulation of cholesterol and glycosphingolipids in the brain and other tissues. Characteristic neurological manifestations of NP-C include saccadic eye movement (SEM) abnormalities or vertical supranuclear gaze palsy (VSGP), cerebellar signs (ataxia, dystonia/dysmetria, dysarthria and dysphagia) and gelastic cataplexy. Epileptic seizures are also common in affected patients. Typically, neurological disease onset occurs during childhood, although an increasing number of cases are being detected and diagnosed during adulthood based on late-onset neurological signs and psychiatric manifestations. Categorization of patients according to age at onset of neurological manifestations (i.e. early-infantile, late-infantile, juvenile and adolescent/adult-onset) can be useful for the evaluation of disease course and treatment responses. The first international guidelines for the clinical management of NP-C in children and adults were published in 2009. Since that time a significant amount of data regarding the epidemiology, detection/diagnosis, and treatment of NP-C has been published. Here, we report points of consensus among experts in the diagnosis and treatment of NP-C based on a follow-up meeting in Paris, France in September 2011. This article serves as an update to the original guidelines providing, among other things, further information on detection/diagnostic methods, potential new methods of monitoring disease progression, and therapy. Treatment goals and the application of disease-specific therapy with miglustat are also re-evaluated.

Impact of selected inborn errors of metabolism on prenatal and neonatal development

In general, data regarding maturational processes of different metabolic pathways in the very vulnerable fetal and neonatal period are rare. This review is to substantiate the impact of selected inborn errors of metabolism on this critical period of life and their clinical manifestation. Significant adaptation of mitochondrial/energy-, carbohydrate-, lysosomal-, and amino acid-metabolism occurs during early prenatal and neonatal development. In utero, metabolic environment has an impact on the development of the fetus as well as fetal organ maturation. Defects of distinct metabolic pathways could therefore already be of significant relevance in utero and for clinical manifestations in the early fetal and neonatal period. Disturbances of these pathways may influence intrauterine growth and health. Production of a toxic intrauterine milieu, energy-deficiency, modification of membrane function, or disturbance of the normal intrauterine expression of genes may be responsible for fetal compromise and developmental disorders. Three categories of metabolic disorders will be discussed: the "intoxication type" (classical galactosemia, ornithine transcarbamylase deficiency, and "maternal phenylketonuria"), the "storage type" (Morbus Niemann Pick type C), and the "energy deficient type" (including long-chain fatty acid oxidation disorders, pyruvate dehydrogenase deficiency, and respiratory chain defects). For these disorders, the pathophysiology of early manifestation, special aspects regarding the prenatal and neonatal period, and diagnostic as well as therapeutic options are presented.

Niemann-Pick disease type C

Niemann-Pick C disease (NP-C) is a neurovisceral atypical lysosomal lipid storage disorder with an estimated minimal incidence of 1/120 000 live births. The broad clinical spectrum ranges from a neonatal rapidly fatal disorder to an adult-onset chronic neurodegenerative disease. The neurological involvement defines the disease severity in most patients but is typically preceded by systemic signs (cholestatic jaundice in the neonatal period or isolated spleno- or hepatosplenomegaly in infancy or childhood). The first neurological symptoms vary with age of onset: delay in developmental motor milestones (early infantile period), gait problems, falls, clumsiness, cataplexy, school problems (late infantile and juvenile period), and ataxia not unfrequently following initial psychiatric disturbances (adult form). The most characteristic sign is vertical supranuclear gaze palsy. The neurological disorder consists mainly of cerebellar ataxia, dysarthria, dysphagia, and progressive dementia. Cataplexy, seizures and dystonia are other common features. NP-C is transmitted in an autosomal recessive manner and is caused by mutations of either the NPC1 (95% of families) or the NPC2 genes. The exact functions of the NPC1 and NPC2 proteins are still unclear. NP-C is currently described as a cellular cholesterol trafficking defect but in the brain, the prominently stored lipids are gangliosides. Clinical examination should include comprehensive neurological and ophthalmological evaluations. The primary laboratory diagnosis requires living skin fibroblasts to demonstrate accumulation of unesterified cholesterol in perinuclear vesicles (lysosomes) after staining with filipin. Pronounced abnormalities are observed in about 80% of the cases, mild to moderate alterations in the remainder ("variant" biochemical phenotype). Genotyping of patients is useful to confirm the diagnosis in the latter patients and essential for future prenatal diagnosis. The differential diagnosis may include other lipidoses; idiopathic neonatal hepatitis and other causes of cholestatic icterus should be considered in neonates, and conditions with cerebellar ataxia, dystonia, cataplexy and supranuclear gaze palsy in older children and adults. Symptomatic management of patients is crucial. A first product, miglustat, has been granted marketing authorization in Europe and several other countries for specific treatment of the neurological manifestations. The prognosis largely correlates with the age at onset of the neurological manifestations.

Niemann-Pick Disease Type C: from molecule to clinic

1. Niemann-Pick Type C disease (NPC) is an incurable cholesterol-storage disorder that stems from inherited deficiencies of lysosomal proteins involved in intracellular lipid-trafficking proteins. The condition manifests as progressive neurological impairment and leads to death at an early age. 2. To improve clinical recognization and investigate therapeutic strategies, recent studies using molecular and genetic approaches have led to significant advances in the creation of animal models of NPC, as well as in the understanding of the cellular and molecular mechanisms underlying the pathogenesis of NPC. 3. Patients with NPC are divided into four groups based on age at presentation, whereas the clinical features of NPC can be divided into five categories based on the severity of the disease. Progressive neuronal loss, especially of cerebellar Purkinje cells, is a hallmark of NPC. Ballooned neurons, axonal abnormalities and astroglyosis are among the pathological changes seen. Severe demyelination is also present in the mouse model of NPC. 4. Mutations in the NPC1 gene cause approximately 95% of cases of NPC, whereas mutations in the NPC2 gene account for the remainder of cases. NPC1 is a transmembrane protein and NPC2 is a soluble protein involved in lipid trafficking in lysosomes. Loss-of-function mutations in the NPC1 gene lead to a failure of the calcium-mediated fusion of endosomes with lysosomes, resulting in the accumulation of cholesterol and other lipids in late endosomes and lysosomes. 5. The present review updates the disorders of NPC from clinical features to animal models and molecular mechanisms.

Metabolism and biological functions of two phosphorylated sphingolipids, sphingosine 1-phosphate and ceramide 1-phosphate

Sphingolipids are major lipid constituents of the eukaryotic plasma membrane. Without certain sphingolipids, cells and/or embryos cannot survive, indicating that sphingolipids possess important physiological functions that are not substituted for by other lipids. One such role may be signaling. Recent studies have revealed that some sphingolipid metabolites, such as long-chain bases (LCBs; sphingosine (Sph) in mammals), long-chain base 1-phosphates (LCBPs; sphingosine 1-phosphate (S1P) in mammals), ceramide (Cer), and ceramide 1-phosphate (C1P), act as signaling molecules. The addition of phosphate groups to LCB/Sph and Cer generates LCBP/S1P and C1P, respectively. These phospholipids exhibit completely different functions than those of their precursors. In this review, we describe recent advances in understanding the functions of LCBP/S1P and C1P in mammals and in the yeast Saccharomyces cerevisiae. Since LCB/Sph, LCBP/S1P, Cer, and C1P are mutually convertible, regulation of not only the total amount of the each lipid but also of the overall balance in cellular levels is important. Therefore, we describe in detail their metabolic pathways, as well as the genes involved in each reaction.

[Fatal neonatal respiratory distress in Niemann-Pick C2 and prenatal diagnosis with mutations in gene HE1/NPC2]

We report the fifth case of neonatal form of type C2 (NP-C2) Niemann-Pick disease with early and fatal respiratory distress. Eleven families presenting such cases are known to date in the world. Since December 2000, isolation of the underlying gene HE1/NPC2 and its mutations has allowed major advances in diagnosis.

CASE REPORT

Elisa was born in May 2000. NP-C2 disease was associated with severe respiratory distress leading to death at the age of four months. On the next pregnancy in September 2000, prenatal diagnosis was performed by means of biological tests that required four weeks response time. In December 2000, isolation of the HE1/NPC2 gene located to 14q24.3 and of some of its mutations allowed to characterize the patient as being homozygote for the nonsense mutation E20X. On the the two next pregnancies, prenatal diagnosis was performed at 12 SA, in 48 hours, by the means of mutation analysis. The last fetus was heterozygote for the mutation E20X, allowing the birth at term of a healthy male newborn baby.

CONCLUSION

Niemann-Pick type C disease is a rare lysosomal lipid storage disease with severe prognosis. It is characterized by abnormalities of intracellular transport of endocytosed cholesterol. Diagnosis relies on biological tests that require cultured cells. Genetic heterogeneity defines two different genetic complementation groups C1 and C2. Severe and early respiratory distress is more likely to be associated with the rare type C2. Since December 2000, after identification of the disease-causing mutations in the proband, mutation analysis of gene HE1/NPC2 on direct chorionic villus samples allows early and fast (48 hours) prenatal diagnosis.

A new fluorimetric enzyme assay for the diagnosis of Niemann-Pick A/B, with specificity of natural sphingomyelinase substrate

6-Hexadecanoylamino-4-methylumbelliferylphosphorylcholine (HMUPC) was shown to be a specific substrate for the determination of acid (lysosomal) sphingomyelinase (ASM; gene SMPD1). Fibroblasts (n = 27) and leukocytes (n = 8) from both the A and B types of Niemann-Pick disease showed < 6% and < 10% of mean normal ASM activity, respectively. Niemann-Pick A or B patients bearing the Q292K mutation had apparently normal ASM activity with our new artificial substrate. These patients with false-normal sphingomyelinase activity, however, could readily be detected by determining the extent of inhibition of enzymatic hydrolysis of the artificial substrate HMU-PC by an unlabelled natural substrate, in particular lysosphingomyelin. This approach is generally applicable. Our novel assay for ASM combines the ease of a rapid and robust enzyme assay using a fluorogenic substrate with the specificity of an ASM assay using a natural substrate. Such assays are obviously more convenient to the diagnostic laboratory, since radiolabelled substrates are not required.

Structure and function of the NPC2 protein

Somatic cell hydridization and linkage studies indicated the implication of a second gene as a cause of Niemann-Pick C disease in a minority (5%) of patients. A study of the lysosomal proteome led to the identification of a previously known gene, HE1, as the NPC2 gene. The mature NPC2/HE1 protein is a ubiquitous soluble small 132-amino-acid glycoprotein, first characterized as a major secretory protein in the human epididymis, but also detected in most tissues. Seventeen families with mutations in the NPC2 gene are known. Good genotype-phenotype correlations were observed. No distinction can be made between the biochemical phenotypes of NPC1 or NPC2 mutants. The NPC2 protein binds cholesterol with submicromolar affinity at neutral and acidic pH. The bovine protein has been crystallized, and the cholesterol-binding site assigned to a hydrophobic loosely packed region. There is strong evidence that the NPC1 and NPC2 proteins must function in a closely related fashion. Current data have led to the hypothesis that NPC2 would bind cholesterol from internal lysosomal membranes, enabling a physical interaction with NPC1 (or another protein) and allowing postlysosomal export of cholesterol. In this model, the activity of NPC1 would depend on that of NPC2. The precise function of the NPC2 protein has, however, not been fully elucidated.

The pathophysiology and mechanisms of NP-C disease

The molecular isolation of NPC1 and NPC2, the genes defective in patients with Niemann-Pick disease type C (NP-C), has heralded in an exponential increase in our understanding of this syndrome and thus of human intracellular sterol transport. Despite this, neither the mechanisms of action nor the substrates for these putative transporters have been defined. In this overview, we describe our perspectives on the current awareness of the genetic determination and cellular biology of this syndrome, with emphasis on the underlying events that lead to neurodegeneration and the manner in which they might eventually be treated.

Niemann-Pick disease type C

Niemann-Pick disease type C (NPC) is an autosomal recessive neurovisceral lipid storage with a wide spectrum of clinical phenotypes. At the cellular level, the disorder is characterized by accumulation of unesterified cholesterol and glycolipids in the lysosomal/late endosomal system. Approximatively 95% of patients have mutations in the NPC1 gene (mapped at 18q11) which encodes a large membrane glycoprotein primarily located to late endosomes. The remainder have mutations in the NPC2 gene (mapped at 14q24.3) which encodes a small soluble lysosomal protein with cholesterol-binding properties. The identical biochemical patterns observed in NPC1 and NPC2 mutants suggest that the two proteins function in a coordinate fashion. Identification of mutations revealed a complex picture of molecular heterogeneity, allowing genotype - phenotype correlations for both genes and providing insights into structure - function relationships for the NPC1 protein. Although a whole body of evidence suggests that the NPC1 and NPC2 proteins are involved in the cellular postlysosomal/late endosomal transport of cholesterol, glycolipids and other cargo, their precise functions and relationship remain unclear and are currently the subject of intense investigation. These studies, conducted in various models, should ultimately lead to a better understanding of the pathophysiology of NPC and new therapeutic approaches.