Mucopolysaccharidosis type VII as a cause of recurrent non-immune hydrops fetalis

Mucopolysaccharidosis VII in Brazil: natural history and clinical findings

Background

Mucopolysaccharidosis type VII (MPS VII), also known as Sly syndrome, caused by deficiency of the lysosomal enzyme β-glucuronidase, is an ultra-rare disorder with scarce epidemiological data and few publications about natural history and clinical spectrum.

Methods

We conducted a case series report which included retrospective data from all MPS VII patients diagnosed through the “MPS Brazil Network” who were known to be alive in 2020 in Brazil (N = 13). Clinical data were obtained from a review of the medical records and descriptive statistics and variables were summarized using counts and percentages of the total population.

Results

The majority of the patients were from the Northeast region of Brazil. Among the signs and symptoms that raised the clinical suspicion of MPS, coarse face was the most frequent; 58% of the patients had a history of non-immune hydrops fetalis. All the subjects presented short neck and trunk. The majority presented typical phenotypical signs of MPS disorders. They all presented neurodevelopmental delay and cognitive impairment. About half of this cohort had knees deformities. Dysostosis multiplex was identified in almost all patients and cardiomyopathy was less frequent than observed in other types of MPSs. The mean age at diagnosis was 5 years, ranging from 1 to 14 years. Almost all patients (12/13) were homozygous for the c.526C>T (p.Leu176Phe) mutation. A novel variant of the GUSB gene was found, the c.875T>C (p.Leu292Pro), in a compound heterozygous with the c.526C>T (p.Leu176Phe) variant.

Conclusions

This case series is the biggest data collection of MPS VII patients alive in Latin America. The overall clinical picture of the MPS VII patients is very similar to other MPS disorders, including a spectrum of severity and delayed diagnosis.

Exome Sequencing for Prenatal Diagnosis in Nonimmune Hydrops Fetalis

BACKGROUND

The cause of most fetal anomalies is not determined prenatally. Exome sequencing has transformed genetic diagnosis after birth, but its usefulness for prenatal diagnosis is still emerging. Nonimmune hydrops fetalis (NIHF), a fetal abnormality that is often lethal, has numerous genetic causes; the extent to which exome sequencing can aid in its diagnosis is unclear.

METHODS

We evaluated a series of 127 consecutive unexplained cases of NIHF that were defined by the presence of fetal ascites, pleural or pericardial effusions, skin edema, cystic hygroma, increased nuchal translucency, or a combination of these conditions. The primary outcome was the diagnostic yield of exome sequencing for detecting genetic variants that were classified as either pathogenic or likely pathogenic according to the criteria of the American College of Medical Genetics and Genomics. Secondary outcomes were the percentage of cases associated with specific genetic disorders and the proportion of variants that were inherited.

RESULTS

In 37 of the 127 cases (29%), we identified diagnostic genetic variants, including those for disorders affecting the RAS-MAPK cell-signaling pathway (known as RASopathies) (30% of the genetic diagnoses); inborn errors of metabolism and musculoskeletal disorders (11% each); lymphatic, neurodevelopmental, cardiovascular, and hematologic disorders (8% each); and others. Prognoses ranged from a relatively mild outcome to death during the perinatal period. Overall, 68% of the cases (25 of 37) with diagnostic variants were autosomal dominant (of which 12% were inherited and 88% were de novo), 27% (10 of 37) were autosomal recessive (of which 95% were inherited and 5% were de novo), 1 was inherited X-linked recessive, and 1 was of uncertain inheritance. We identified potentially diagnostic variants in an additional 12 cases.

CONCLUSIONS

In this large case series of 127 fetuses with unexplained NIHF, we identified a diagnostic genetic variant in approximately one third of the cases. (Funded by the UCSF Center for Maternal-Fetal Precision Medicine and others; ClinicalTrials.gov number, NCT03412760.).

Relevance of the Materno-Fetal Interface for the Induction of Antigen-Specific Immune Tolerance

In humans, maternal IgGs are transferred to the fetus from the second trimester of pregnancy onwards. The transplacental delivery of maternal IgG is mediated by its binding to the neonatal Fc receptor (FcRn) after endocytosis by the syncytiotrophoblast. IgGs present in the maternal milk are also transferred to the newborn through the digestive epithelium upon binding to the FcRn. Importantly, the binding of IgGs to the FcRn is also responsible for the recycling of circulating IgGs that confers them with a long half-life. Maternally delivered IgG provides passive immunity to the newborn, for instance by conferring protective anti-flu or anti-pertussis toxin IgGs. It may, however, lead to the development of autoimmune manifestations when pathological autoantibodies from the mother cross the placenta and reach the circulation of the fetus. In recent years, strategies that exploit the transplacental delivery of antigen/IgG complexes or of Fc-fused proteins have been validated in mouse models of human diseases to impose antigen-specific tolerance, particularly in the case of Fc-fused factor VIII (FVIII) domains in hemophilia A mice or pre-pro-insulin (PPI) in the case of preclinical models of type 1 diabetes (T1D). The present review summarizes the mechanisms underlying the FcRn-mediated transcytosis of IgGs, the physiopathological relevance of this phenomenon, and the repercussion for drug delivery and shaping of the immune system during its ontogeny.

A system-based approach to the genetic etiologies of non-immune hydrops fetalis

A wide spectrum of genetic causes may lead to nonimmune hydrops fetalis (NIHF), and a thorough phenotypic and genetic evaluation are essential to determine the underlying etiology, optimally manage these pregnancies, and inform discussions about anticipated prognosis. In this review, we outline the known genetic etiologies of NIHF by fetal organ system affected, and provide a systematic approach to the evaluation of NIHF. Some of the underlying genetic disorders are associated with characteristic phenotypic features that may be seen on prenatal ultrasound, such as hepatomegaly with lysosomal storage disorders, hyperechoic kidneys with congenital nephrosis, or pulmonary valve stenosis with RASopathies. However, this is not always the case, and the approach to evaluation must include prenatal ultrasound findings as well as genetic testing and many other factors. Genetic testing that has been utilized for NIHF ranges from standard chromosomal microarray or karyotype to gene panels and broad approaches such as whole exome sequencing. Family and obstetric history, as well as pathology examination, can yield additional clues that are helpful in establishing a diagnosis. A systematic approach to evaluation can guide a more targeted approach to genetic evaluation, diagnosis, and management of NIHF.

Nonimmune hydrops fetalis: identifying the underlying genetic etiology

PURPOSE

Numerous etiologies may lead to nonimmune hydrops fetalis (NIHF), and the underlying cause often remains unclear. We aimed to determine the proportion of NIHF cases in which the etiology was clearly determined in a large, contemporary, and diverse cohort, as well as to describe the etiologies with a focus on genetic causes.

METHODS

Retrospective review of NIHF cases between 2015 and 2017 from the five University of California Fetal-Maternal Consortium sites. Singleton pregnancies with prenatally diagnosed NIHF were included, and cases with maternal alloimmunization were excluded. Cases were categorized as being of confirmed, suspected, or unknown etiology.

RESULTS

Sixty-five NIHF cases were identified. Forty-six percent (30/65) remained of unknown etiology, while 9.2% (6/65) had a suspected etiology and 44.6% (29/65) were of confirmed etiology. Among confirmed cases, 11 resulted from aneuploidy; 7 from fetal structural anomalies; 2 each from fetal arrhythmia, Noonan syndrome, and generalized lymphatic dysplasia; and 1 each from arthrogryposis, parvovirus, neonatal alloimmune thrombocytopenia, fetal goiter, and Kasabach-Merritt syndrome.

CONCLUSION

In this contemporary, multicenter study, the cause of prenatally diagnosed NIHF was confirmed in only 44% of cases, and a genetic etiology was found in only 25% of those that received standard of care genetic testing.

Lysosomal Storage Disorders in Nonimmune Hydrops Fetalis (NIHF): An Indian Experience

Lysosomal storage disorders (LSD) are rare inherited neurovisceral inborn errors of metabolism which may present as nonimmune hydrops fetalis (NIHF) during pregnancy. Although causes of NIHF are highly diverse, LSDs are one of the underlying causes of NIHF. The aim of this study was to elucidate most frequent causes of LSDs presenting as NIHF in Indian population. Several fetal tissues were investigated for enzymatic diagnosis of LSDs using modified fluorometric assays in the current prospective study carried out at our national tertiary center from 2006 through 2016. Other general causes of NIHF were ruled out. Twenty-one percent (7/33) of cases were confirmed to have LSDs. Two patients were diagnosed with Hurler syndrome; two had Sly syndrome and one each of Niemann-Pick disease type A/B, Gaucher's disease, and mucolipidosis. Four of eleven cases (36%) with recurrent NIHF were found to have LSDs. In spite of extreme rarity of LSDs, they should be considered as a potential cause of NIHF, especially with recurrent NIHF. Specific investigations of LSD leading to definitive diagnosis may aid the clinician in providing accurate genetic counseling and prenatal diagnosis to the patients and help in subsequent pregnancies to the families. Furthermore, early intervention and management with enzyme replacement therapy may be planned for the lysosomal storage disorders where available.

[Mucopolysaccharidosis: clinical features, diagnosis and management]

The mucopolysaccharidoses (MPS) are a group of rare (orphan) diseases, characterised by a deficiency of enzymes involved in the metabolism of glycosaminoglycans (GAGs) at lysosomal level. When there is a deficiency of a particular enzyme there is an accumulation of GAGs in the cells resulting in progressive cellular damage, which can affect multiple organ systems and lead to organ failure. Diagnosis is based on knowledge of the clinical manifestations, performing biochemical analyses to identify the type of GAG that is accumulating, and confirm the type of disorder with the corresponding enzymatic determination. Their identification is essential to initiate early treatment, taking into account that multidisciplinary management and enzyme replacement therapy is available for MPS I (Hurler syndrome), MPS II (Hunter syndrome), MPS IV (Morquio syndrome), and MPS VI (Maroteaux-Lamy syndrome. In this review, an analysis is made of each of these syndromes, as well as their diagnosis and treatment.

Radiological and clinical characterization of the lysosomal storage disorders: non-lipid disorders

Lysosomal storage diseases (LSDs) are a large group of genetic metabolic disorders that result in the accumulation of abnormal material, such as mucopolysaccharides, glycoproteins, amino acids and lipids, within cells. Since many LSDs manifest during infancy or early childhood, with potentially devastating consequences if left untreated, timely identification is imperative to prevent irreversible damage and early death. In this review, the key imaging features of the non-lipid or extralipid LSDs are examined and correlated with salient clinical manifestations and genetic information. Disorders are stratified based on the type of excess material causing tissue or organ dysfunction, with descriptions of the mucopolysaccharidoses, mucolipidoses, alpha-mannosidosis, glycogen storage disorder II and cystinosis. In addition, similarities and differences in radiological findings between each of these LSDs are highlighted to facilitate further recognition. Given the rare and extensive nature of the LSDs, mastery of their multiple clinical and radiological traits may seem challenging. However, an understanding of the distinguishing imaging characteristics of LSDs and their clinical correlates may allow radiologists to play a key role in the early diagnosis of these progressive and potentially fatal disorders.

Lysosomal storage disorder in non-immunological hydrops fetalis (NIHF): more common than assumed? Report of four cases with transient NIHF and a review of the literature

Background

Lysosomal storage disorders (LSD) are a rare cause of non immunological hydrops fetalis (NIHF) and congenital ascites. The reported incidence is about 1%. The incidence of idiopathic NIHF is estimated to be about 18%.

Patients and methods

We report four cases with transient hydrops fetalis resulting from LSD and performed a literature review on LSD with NIHF and congenital ascites in combination.

Results

At present, 12 different LSDs are described to be associated with NIHF or congenital ascites. Most patients had a family history of NIHF, where the preceding sibling had not been examined. A diagnostic approach to the fetus with NIHF due to suspected LSD either in utero or postnatal is suggested. Transient forms of NIHF and/or ascites in association with MPS IVA, MPS VII and NPC are described for the first time in this publication.

Conclusions

LSD should be considered in transient hydrops. Enzymatic studies in chorionic villous sample or amniotic cultured cells, once the most common conditions associated with fetal ascites or hydrops have been ruled out, are important. This paper emphasizes the fact that LSD is significantly higher than the estimated 1% in previous studies, which is important for genetic counseling as there is a high risk of recurrence and the availability of enzyme replacement therapy for an increasing number of LSD.

New strategies for enzyme replacement therapy for lysosomal storage diseases

Enzyme replacement therapy is an established means of treating lysosomal storage diseases. Infused enzymes are normally targeted to the lysosomes of affected cells by interactions with cell-surface receptors that recognize carbohydrate moieties such as mannose and mannose 6-phosphate on the enzymes. Therefore, we have investigated alternative strategies to deliver the lysosomal enzyme beta-glucuronidase in the enzyme-deficient mucopolysaccharidosis type VII mouse model. Here we summarize our recent efforts to use nontraditional ways to deliver beta-glucuronidase. First, we used a chimeric protein of the insulin-like growth factor II (IGF-II) fused to beta-glucuronidase to deliver enzyme via the IGF-II binding site on the bifunctional IGF-II/mannose 6-phosphate receptor. Second, we used the 11-amino-acid human immunodeficiency virus (HIV) Tat domain fused to beta-glucuronidase to mediate uptake by absorptive endocytosis. Interaction with heparan sulfate on the cell surface internalizes and delivers the Tat-tagged enzyme to the lysosome via plasma membrane recycling. Third, we created a chimeric beta-glucuronidase fused to the Fc portion of human immunoglobulin G (IgG) Fc, which was transported by the neonatal Fc receptor from the maternal circulation across the placenta to sites of storage in fetal tissues. Finally, periodate treatment was used to eliminate interaction with carbohydrate receptors, creating an enzyme with increased plasma half-life, resulting in transport across the blood-brain barrier and clearance of storage in neurons. These strategies for delivering lysosomal enzymes could also be used to target nonlysosomal proteins or enzymes identified for bioremediation of other conditions.

Infused Fc-tagged beta-glucuronidase crosses the placenta and produces clearance of storage in utero in mucopolysaccharidosis VII mice

Glycosaminoglycan storage begins in prenatal life in patients with mucopolysaccharidosis (MPS). In fact, prenatal hydrops is a common manifestation of MPS VII because of beta-glucuronidase (GUS) deficiency. One way to address prenatal storage might be to deliver the missing enzyme across the placenta into the fetal circulation. Maternal IgG is transported across the placenta by the neonatal Fc receptor (FcRn), which recognizes the Fc domain of IgG and mediates transcytosis from maternal to fetal circulation. We hypothesized that we could exploit this process to deliver corrective enzyme to the fetus. To test this hypothesis, the C-terminal fusion protein, GUS-Fc, was compared with native, untagged, recombinant GUS for clearance from the maternal circulation, delivery to the fetus, and reduction of lysosomal storage in offspring of MPS VII mice. We observed that GUS-Fc, infused into pregnant mothers on embryonic days 17 and 18, was transported across the placenta. Similarly infused untagged GUS was not delivered to the fetus. GUS-Fc plasma enzyme activity in newborn MPS VII mice was 1,000 times that seen after administration of untagged GUS and approximately 100 times that of untreated WT newborns. Reduced lysosomal storage in heart valves, liver, and spleen provided evidence that in utero enzyme replacement therapy with GUS-Fc targeted sites of storage in the MPS VII fetus. We hypothesize that this noninvasive approach could deliver the missing lysosomal enzyme to a fetus with any lysosomal storage disease. It might also provide a method for inducing immune tolerance to the missing enzyme or another foreign protein.

Recurrent Fetal Hydrops due to Mucopolysaccharidoses Type VII

Hydrops fetalis is associated with a wide range of abnormalities. In about 20% of cases of non-immune fetal hydrops, no cause is found despite investigations including routine post-mortem examination and enzyme studies may be indicated to detect an underlying metabolic storage disease. Fetal hydrops due to mucopolysaccharidosis type VII is very rare and a prenatal diagnosis is not usually made. We report a case of mucopolysaccharidosis type VII presenting as recurrent fetal hydrops and review the clinico-pathological features of this disorder.