Prenatal diagnosis and fetal pathology in a Turkish family harboring a novel nonsense mutation in the lysosomal alpha-N-acetyl-neuraminidase (sialidase) gene

Stillbirth Investigations: An Iconographic and Concise Diagnostic Workup in Perinatal Pathology

Introduction  Stillbirth is a dramatic event for the parents, health care team, and anyone close to the expectant parents. Multidisciplinary team (MDT) meetings are essential to improve communication in health care. We review the most frequent findings discussed at MDT meetings. Methods  A PubMed search was conducted through December 2021 since the inception (1965) using clinical queries with the key terms "stillbirth" AND "investigation" AND "pathology" AND "human." The search strategy included reviews, meta-analyses, randomized controlled trials, clinical trials, and observational studies. This systematic review is based on, but not limited to, the search results. It is the experience of more than 30 years of pediatrics, obstetrics, and pathology staff. Results  Two hundred and six articles were screened and complemented through the perusal of congressional activities and personal communications. Pathological findings following perinatal death can be divided into macroscopic, histologic, and placental findings. The placenta is crucial in fetal medicine and is key in determining the cause of stillbirth in a substantial number of events. Perinatal lung disease is essential to evaluate the response of newborns to extrauterine life and address newborns' outcomes appropriately. Conclusions  Stillbirth remains one of the less explored areas of medicine, and we can determine the cause in a limited number of cases. Nevertheless, placental pathology is critical in the etiology discovery pathway. Accurate investigations and discussion of photography-supported findings are vital in promoting communication at MDT meetings.

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.

NEU1—A Unique Therapeutic Target for Alzheimer’s Disease

Neuraminidase 1 (NEU1) is considered to be the most abundant and ubiquitous mammalian enzyme, with a broad tissue distribution. It plays a crucial role in a variety of cellular mechanisms. The deficiency of NEU1 has been implicated in various pathological manifestations of sialidosis and neurodegeneration. Thus, it is a novel therapeutic target for neurodegenerative changes in the Alzheimer’s brain. However, to manipulate NEU1 as a therapeutic target, it is imperative to understand that, although NEU1 is commonly known for its lysosomal catabolic function, it is also involved in other pathways. NEU1 is involved in immune response modulation, elastic fiber assembly modulation, insulin signaling, and cell proliferation. In recent years, our knowledge of NEU1 has continued to grow, yet, at the present moment, current data is still limited. In addition, the unique biochemical properties of NEU1 make it challenging to target it as an effective therapeutic option for sialidosis, which is a rare disease but has an enormous patient burden. However, the fact that NEU1 has been linked to the pathology of Alzheimer’s disease, which is rapidly growing worldwide, makes it more relevant to be studied and explored. In the present study, the authors have discussed various cellular mechanisms involving NEU1 and how they are relevant to sialidosis and Alzheimer’s disease.

Cardiovascular involvement in alpha-n-acetyl neuraminidase deficiency syndromes (sialidosis type I and II)

Sialidosis, a rare autosomal recessive disorder, is caused by a deficiency of NEU1 encoded enzyme alpha-N-acetyl neuraminidase. We report a premature male with neonatal-onset type II sialidosis which was associated with left ventricular dysfunction. The clinical presentation and subsequent progression which culminated in his untimely death at 16 months of age are succinctly described. Early-onset cardiovascular involvement as noted in this patient is not well characterised. The case report is supplemented by a comprehensive review of the determinants, characteristics, and the clinical course of cardiovascular involvement in this rare condition.

Promptly reporting of critical laboratory values in pediatrics: A work in progress

In the 21^st century, the determination of alert thresholds remains the most challenging and controversial issue in clinical pediatrics. Pre-analytical, analytical, and post-analytical matters will consolidate or undermine the fate of any laboratory process. Pre-analytical issues need to be cleared off before the laboratory physician can dispatch the result to the pediatrician in charge. Once it is cleared off, the classification of essential laboratory results is paramount. It is more than an academic exercise and may be subdivided in the order of priority we handle it to inform promptly and safely the primary physicians. Currently, we are applying new modes of making sure relevant information is transmitted without interrupting the standard workflow of the primary physicians in charge for the child, who eventually need a fast line of action for results that may be life-threatening.

Sialidosis: A Review of Morphology and Molecular Biology of a Rare Pediatric Disorder

Sialidosis (MIM 256550) is a rare, autosomal recessive inherited disorder, caused by α-N-acetyl neuraminidase deficiency resulting from a mutation in the neuraminidase gene (NEU1), located on 6p21.33. This genetic alteration leads to abnormal intracellular accumulation as well as urinary excretion of sialyloligosaccharides. A definitive diagnosis is made after the identification of a mutation in the NEU1 gene. So far, 40 mutations of NEU1 have been reported. An association exists between the impact of the individual mutations and the severity of clinical presentation of sialidosis. According to the clinical symptoms, sialidosis has been divided into two subtypes with different ages of onset and severity, including sialidosis type I (normomorphic or mild form) and sialidosis type II (dysmorphic or severe form). Sialidosis II is further subdivided into (i) congenital; (ii) infantile; and (iii) juvenile. Despite being uncommon, sialidosis has enormous clinical relevance due to its debilitating character. A complete understanding of the underlying pathology remains a challenge, which in turn limits the development of effective therapeutic strategies. Furthermore, in the last few years, some atypical cases of sialidosis have been reported as well. We herein attempt to combine and discuss the underlying molecular biology, the clinical features, and the morphological patterns of sialidosis type I and II.

Pathogenesis, Emerging therapeutic targets and Treatment in Sialidosis

INTRODUCTION

Sialidosis is a neurosomatic, lysosomal storage disease (LSD) caused by mutations in the NEU1 gene, encoding the lysosomal sialidase NEU1. Deficient enzyme activity results in impaired processing/degradation of sialo-glycoproteins, and accumulation of oversialylated metabolites. Sialidosis is considered an orphan disorder for which no therapy is currently available.

AREAS COVERED

The review describes the clinical forms of sialidosis and the NEU1 mutations so far identified; NEU1 requirement to complex with the protective protein/cathepsin A for stability and activation; and the pathogenic effects of NEU1 deficiency. Studies of the molecular mechanisms of pathogenesis in animal models uncovered basic cellular pathways downstream of NEU1 and its substrates, which may be implicated in more common adult (neurodegenerative) diseases. The development of a Phase I/II clinical trial for patients with galactosialidosis may prove suitable for sialidosis patients with the attenuated form of the disease.

EXPERT OPINION

Recently, there has been a renewed interest in the development of therapies for orphan LSDs, like sialidosis. Given the small number of potentially eligible patients, the way to treat sialidosis would be through the coordinated effort of clinical centers, which provide diagnosis and care for these patients, and the basic research labs that work towards understanding the disease pathogenesis.

QTLs for murine red blood cell parameters in LG/J and SM/J F(2) and advanced intercross lines

Red blood cells are essential for oxygen transport and other physiologic processes. Red cell characteristics are typically determined by complete blood counts which measure parameters such as hemoglobin levels and mean corpuscular volumes; these parameters reflect the quality and quantity of red cells in the circulation at any particular moment. To identify the genetic determinants of red cell parameters, we performed genome-wide association analysis on LG/J×SM/J F2 and F34 advanced intercross lines using single nucleotide polymorphism genotyping and a novel algorithm for mapping in the combined populations. We identified significant quantitative trait loci for red cell parameters on chromosomes 6, 7, 8, 10, 12, and 17; our use of advanced intercross lines reduced the quantitative trait loci interval width from 1.6- to 9.4-fold. Using the genomic sequences of LG/J and SM/J mice, we identified nonsynonymous coding single nucleotide polymorphisms in candidate genes residing within quantitative trait loci and performed sequence alignments and molecular modeling to gauge the potential impact of amino acid substitutions. These results should aid in the identification of genes critical for red cell physiology and metabolism and demonstrate the utility of advanced intercross lines in uncovering genetic determinants of inherited traits.

Impact of beta-galactosidase mutations on the expression of the canine lysosomal multienzyme complex

beta-galactosidase (GLB1) forms a functional lysosomal multienzyme complex with lysosomal protective protein (PPCA) and neuraminidase 1 (NEU1) which is important for its intracellular processing and activity. Mutations in the beta-galactosidase gene cause the lysosomal storage disease G(M1)-gangliosidosis. In order to identify additional molecular changes associated with the presence of beta-galactosidase mutations, the expression of canine lysosomal multienzyme complex components in GLB1(+/+), GLB1(+/-) and GLB1(-/-) fibroblasts was investigated by quantitative RT-PCR, Western blot and enzymatic assays. Quantitative RT-PCR revealed differential regulation of total beta-galactosidase, beta-galactosidase variants and protective protein for beta-galactosidase gene (PPGB) in GLB1(+/-) and GLB1(-/-) compared to GLB1(+/+) fibroblasts. Furthermore, it was shown that PPGB levels gradually increased with the number of mutant beta-galactosidase alleles while no change in the NEU1 expression was observed. This is the first study that simultaneously examine the effect of GLB1(+/+), GLB1(+/-) and GLB1(-/-) genotypes on the expression of lysosomal multienzyme complex components. The findings reveal a possible adaptive process in GLB1 homozygous mutant and heterozygous individuals that could facilitate the design of efficient therapeutic strategies.

Type II sialidosis: review of the clinical spectrum and identification of a new splicing defect with chitotriosidase assessment in two patients

Sialidosis is a lysosomal storage disease caused by the deficiency of alpha-N-acetyl neuraminidase-1 (NEU1). Sialidosis is classified into two main clinical variants: Type I, the milder form of the disease, and Type II, which can in turn be subdivided into three forms: congenital, infantile and juvenile. We report herein the clinical, biochemical and molecular characterisation of two patients with Type II sialidosis exhibiting the congenital (P1) and infantile forms (P2). We also review clinical data on the rare Type II forms of sialidosis in the hope of improving understanding of the disorder and facilitating its diagnosis. The genetic characterization of the two patients showed one known [c. 679G > A (p.G227R)] NEU1 missense mutation (detected in P2), and the new c.807 + 1G > A splicing defect (detected in P1), a genetic lesion that is extremely rare in this disease. Interestingly, P2 presented an extremely elevated level of chitotriosidase in plasma. This is the first pathological detection of chitotriosidase in sialidosis patients.

Lysosomal storage disorders in the newborn

Lysosomal storage disorders are rare inborn errors of metabolism, with a combined incidence of 1 in 1500 to 7000 live births. These relatively rare disorders are seldom considered when evaluating a sick newborn. A significant number of the >50 different lysosomal storage disorders, however, do manifest in the neonatal period and should be part of the differential diagnosis of several perinatal phenotypes. We review the earliest clinical features, diagnostic tests, and treatment options for lysosomal storage disorders that can present in the newborn. Although many of the lysosomal storage disorders are characterized by a range in phenotypes, the focus of this review is on the specific symptoms and clinical findings that present in the perinatal period, including neurologic, respiratory, endocrine, and cardiovascular manifestations, dysmorphic features, hepatosplenomegaly, skin or ocular involvement, and hydrops fetalis/congenital ascites. A greater awareness of these features may help to reduce misdiagnosis and promote the early detection of lysosomal storage disorders. Implementing therapy at the earliest stage possible is crucial for several of the lysosomal storage disorders; hence, an early appreciation of these disorders by physicians who treat newborns is essential.

Molecular pathology of NEU1 gene in sialidosis

Lysosomal sialidase (EC 3.2.1.18) has a dual physiological function; it participates in intralysosomal catabolism of sialylated glycoconjugates and is involved in cellular immune response. Mutations in the sialidase gene NEU1, located on chromosome 6p21.3, result in autosomal recessive disorder, sialidosis, which is characterized by the progressive lysosomal storage of sialylated glycopeptides and oligosaccharides. Sialidosis type I is a milder, late-onset, normosomatic form of the disorder. Type I patients develop visual defects, myoclonus syndrome, cherry-red macular spots, ataxia, hyperreflexia, and seizures. The severe early-onset form, sialidosis type II, is also associated with dysostosis multiplex, Hurler-like phenotype, mental retardation, and hepatosplenomegaly. We summarize information on the 34 unique mutations determined so far in the sialidase gene, including four novel missense and one novel nonsense mutations found in two Czech and two French sialidosis patients. The analysis of sialidase mutations in sialidosis revealed considerable molecular heterogeneity, reflecting the diversity of clinical phenotypes that make molecular diagnosis difficult. The majority of sialidosis patients have had missense mutations, many of which have been expressed; their effects on activity, stability, intracellular localization, and supramolecular organization of sialidase were studied. A structural model of sialidase allowed us to localize mutations in the sialidase molecule and to predict their impact on the tertiary structure and biochemical properties of the enzyme.

Recent development in mammalian sialidase molecular biology

This review summarizes the recent research development on mammalian sialidase molecular cloning. Sialic acid-containing compounds are involved in several physiological processes, and sialidases, as glycohydrolytic enzymes that remove sialic acid residues, play a pivotal role as well. Sialidases hydrolyze the nonreducing, terminal sialic acid linkage in various natural substrates, such as glycoproteins, glycolipids, gangliosides, and polysaccharides. Mammalian sialidases are present in several tissues/organs and cells with a typical subcellular distribution: they are the lysosomal, the cytosolic, and the plasma membrane-associated sialidases. Starting in 1993, 12 different mammalian sialidases have been cloned and sequenced. A comparison of their amino acid sequences revealed the presence of highly conserved regions. These conserved regions are shared with viral and microbial sialidases that have been characterized at three-dimensional structural level, allowing us to perform the molecular modeling of the mammalian proteins and suggesting a monophyletic origin of the sialidase enzymes. Overall, the availability of the cDNA species encoding mammalian sialidases is an important step leading toward a comprehensive picture of the relationships between the structure and biological function of these enzymes.