Lysosomal Storage Disorders as an Etiology of Nonimmune Hydrops Fetalis: A Systematic Review

Abstract

We performed a systematic review of the literature to evaluate the incidence and types of lysosomal storage disorders (LSD) in case series of nonimmune hydrops fetalis (NIHF). PubMed and Ovid were reviewed for case series evaluating the workup of NIHF diagnosed in utero or in the neonatal period in human subjects from 1979 to August 2020. Retrospective case series with at least five cases of fetal and/or neonatal NIHF with its workup mentioned were identified. Idiopathic NIHF was defined as NIHF without an apparent cause after initial standard-of-care workup. In total, twenty-two case series with 2,678 total cases of NIHF were identified. The overall incidence of LSD was 6.6% (177/2,663) in NIHF cases that were tested for any LSD, and 8.2% (177/2,151) in idiopathic NIHF cases. The most common LSD identified in cases of NIHF were mucopolysaccharidosis type VII, galactosialidosis, infantile sialic acid storage disease, Gaucher disease, GM1 gangliosidosis and sialidosis. More than 40% of the most common LSD causes of NIHF have a potential postnatal treatment. LSD testing for NIHF allows for early diagnosis, better counseling and appropriate management, planning for possible early treatment, and counseling for recurrence risk.

Graphical Abstract

Introduction

Hydrops fetalis is the pathologic accumulation of fluid within fetal extravascular compartments and body cavities. It is usually diagnosed with prenatal ultrasound by the presence of two or more abnormal fluid collections within the fetus, including ascites, pleural effusion, pericardial effusion, and skin edema, and has often been associated with increased placental thickening and polyhydramnios.¹

Historically, most cases of hydrops fetalis were associated with Rh alloimmunization. However, since the widespread use of Rh(d) immune globulin, the occurrence of hydrops fetalis has decreased significantly. Nonimmune hydrops fetalis (NIHF), instances of hydrops not related to alloimmunization, now accounts for more than ninety percent of cases.² Multiple etiologies lead to NIHF, most commonly cardiovascular pathologies, structural malformations, chromosomal abnormalities, single gene disorders, and congenital infections.¹ The most common etiologies of NIHF according to the Society for Maternal Fetal Medicine are cardiovascular abnormalities, including structural and functional, chromosomal abnormalities, fetal anemia and other hematologic causes and prenatal infections.² However, with this extensive list of potential causes, the diagnosis depends on the extent of the workup. Cases without a clear etiology are considered unexplained or idiopathic.

Lysosomal storage disorders (LSD) represent one metabolic cause of NIHF. LSD are caused by defects in the hydrolysis of macromolecules, like lipids and carbohydrates, the transport of lysosomal metabolites, or the packaging of lysosomal enzymes.³ This results in the accumulation of un-degraded material, hindering normal cellular function and triggering a cascade of pathological outcomes.³ The mechanism by which LSD cause NIHF is not entirely clear, but could be secondary to venous obstruction caused by hepatosplenomegaly, heart failure, anemia, or hypoproteinemia. Prenatal diagnosis of LSD can be performed via enzymatic analysis of fetal cells obtained from chorionic villus sampling or amniocentesis or via molecular genetic testing using a hydrops gene panel or exome sequencing.^4-6

LSD have been reported to account for about 1–15% of causes of NIHF cases.^4,7–10 However, they are typically not evaluated for in the initial standard-of-care workup for hydrops fetalis. In 2014, our group performed a comprehensive review of the literature to evaluate the significance of LSD as the underlying etiology of NIHF.¹⁰ Since that review, other large studies have been published changing our conclusion for the most common LSD causing NIHF. Our primary objective was to determine the incidence of each LSD in NIHF where LSD were tested. Our secondary objective was to determine the fraction of LSD that have available treatment.

Methods

PubMed, Ovid, and clinicaltrials.gov were reviewed for case series evaluating the workup of NIHF diagnosed in utero or in the neonatal period in human subjects. Search terms were ‘nonimmune hydrops,’ ‘non immune hydrops,’ ‘metabolic genetic disorders,’ ‘lysosomal storage disorders,’ ‘inborn errors of metabolism,’ and ‘inherited metabolic diseases.’ The time period searched was 1979 to August 2020. Exclusion criteria were: studies published in languages other than English, abstracts, unpublished studies and review articles. The literature search was supplemented by reviewing relevant citations in the initial studies identified. Two investigators (N.I. and A.G.) performed the literature search.

Retrospective studies and case series of NIHF were identified. We included manuscripts with at least five cases of NIHF to minimize publication bias. Two reviewers (N.I. and A.G.) screened all manuscripts independently initially, and then the results were reviewed together. References for included articles are provided below. Excluded articles can be provided upon request. The criteria for the diagnosis of NIHF in each study were recorded. In each article reporting the workup of NIHF, the details of the workup (e.g., ultrasound, karyotype, etc.) were also recorded. Each case series was evaluated for LSD testing to identify which LSD were screened and how many cases of NIHF were caused by these LSD. Only cases of LSD confirmed by enzymatic or genetic tests were included. Prenatal versus postnatal workup were recorded. If no diagnosis was identified as a probable cause for the NIHF, the case was defined as ‘idiopathic.’ The PRISMA guidelines were followed for systematic review of observational studies.¹¹ This study was exempt from Institutional Review Board approval. Our review was registered in PROSPERO (CRD42020165485).

Results

Following our literature search, 2,623 titles were originally identified over the specified time period. After eliminating duplicate titles and studies not pertaining to NIHF and LSD, 1,005 titles remained. Abstracts were reviewed for whether or not these studies met our inclusion criteria, leaving 146 articles for full text review. After evaluating these articles and their references, 22 studies were identified that met our inclusion criteria.^{3,4,7,12–30} Figure 1 shows the PRISMA flow diagram. The study by Al-Kouatly et al³ included 28 cases of LSD between January 2006 and December 2018. However, the controls (n=98) in that study were available only from January 2015 to December 2018 where only 13 LSD cases were identified. The entire cohort of 28 LSD cases was used for the spectrum of LSD in NIHF. For the calculation of the incidence of LSD in NIHF, and among idiopathic cases of NIHF, we used the 13 LSD cases and 98 NIHF LSD negative controls.

Figure 1.

PRISMA Flowchart for screening of articles included in review

In the 22 case series of NIHF where LSD workup was performed, each study diagnosed NIHF with slightly different criteria (Table 1). The methodology for diagnosis of NIHF was not specified in six studies (27.3%).^{3,4,13,16,25,28} Most studies (59.1%) did not provide the exact list of LSD tested for (Table 1). Among the studies where specific LSD testing was not disclosed, it was not evident if every case underwent LSD testing. The majority (54.5%) of studies noted both prenatal and postnatal testing for LSD as part of their NIHF workup.

Table 1.

Case series of Nonimmune Hydrops Fetalis (NIHF) reporting Lysosomal Storage Disorder (LSD) testing

Author/ year (oldest to newest)	Country	Cases of NIHF	Criteria for diagnosis of NIHF	NIHF initial work-up	List of metabolic diseases tested for	Enzymatic vs. molecular testing	Prenatal vs. postnatal work-up	Comments
Mahony 1984	USA	27	“Generalized skin thickening…and/or two or more of the following were demonstrated: placental enlargement, pericardial effusion, pleural effusion, and ascites”	Ultrasound, other work-up not specified	Not specified	Not specified	Prenatal
Im 1984	Canada	20	By ultrasound: “a double fetal abdominal or scalp contour and fetal ascites. Postmortem “generalized edema, accumulation of fluid in fetal serous compartments and edema throughout placenta”	Ultrasound, other work-up not specified	Not specified	Not specified	Both
McFadden 1989	Canada	90	“NIHF listed as a diagnosis [from autopsy] or with criteria for the diagnosis of NIHF”	Autopsy	Not specified	Not specified	Postnatal
McCoy 1995	USA	82	“Fluid in two or more fetal cavities without evidence of isoimmunization”	Detailed ultrasound, thoracentesis, paracentesis, karyotype, autopsy	Not specified	Not specified	Both
Rejjal 1996	Saudi Arabia	17	“Presence of two or more of the following features by prenatal ultrasound: generalized gross subcutaneous edema, ascites, pleural effusion, pericardial effusion, plus the absence of antibodies to red blood cell antigens”	Ultrasound, CBC, maternal antibody screen, TORCH titers, Parvovirus B19, fetal echocardiogram, chromosomal analysis	Not specified	Not specified	Both
Piraud 1996	France	54	Not specified	Not specified	Amniotic fluid supernatant analysis and biochemical study of cultured amniotic fluid cells were investigated for LSD	Enzymatic	Prenatal
Groener 1999	Netherlands	17	“Excessive fluid accumulation within fetal extra-vascular compartments and body cavities in cases not caused by red cell allo-immunization”	Fetal blood samples	Gaucher disease GM1-gangliosidosis Mucopolysaccharidosis IVa Mucopolysaccharidosis VII	Enzymatic	Prenatal
Has 2001	Turkey	30	“Edema with effusion in at least one body cavity and skin edema or serous effusion in more than one body space”	Ultrasound, maternal type & screen, TORCH titers, Parvovirus B19, fetal echocardiogram, karyotype, autopsy, “metabolic testing”	“Investigation for metabolic syndromes in selected cases”	Not specified	Both
Mascaretti 2003	Brazil	29	“One or more clinical signs, such as anasarca, peripheral edema, ascites, pericardial and/or pleural effusions, anemia, congestive heart failure, and hypoalbuminemia”	Ultrasound, CBC, maternal type and screen, “infectious work-up,” fetal echocardiogram, karyotype, autopsy	Not specified	Molecular	Both
Burin 2004	Brazil	33	Not specified	Ultrasound, CBC, maternal type and screen, hemoglobin electrophoresis, TORCH titers, Parvovirus B19, Coxsackie virus, fetal echocardiogram, specific enzymatic analysis for LSD by amniocentesis, karyotype, autopsy	Gaucher disease GM1-gangliosidosis Infantile sialic acid storage disease Mucolipidosis II Mucopolysaccharidosis I Mucopolysaccharidosis II Mucopolysaccharidosis IVa Mucopolysaccharidosis VII Niemann-Pick A/B Sialidosis	Enzymatic	Both	Reference center for LSD
Favre 2004	France	79	“Increased fluid accumulation in fetal soft tissues and serous cavities in >1 site”	Ultrasound, maternal type and screen, TORCH titers, Parvovirus B19, amniocentesis for CMV and Toxoplasmosis, fetal echocardiogram, karyotype, autopsy	Not specified	Enzymatic (“Metabolic disease analysis”)	Postnatal	This study looked at both fetal hydrops and isolated ascites
Rodriguez 2005	USA	32	“Generalized soft tissue edema and presence of fluid in at least one of the pericardial, pleural, or peritoneal cavities”	Ultrasound, CBC, maternal type & screen, RPR, blood cultures, “infectious work up”, autopsy	Tested enzyme levels on autopsy	Enzymatic	Postnatal	One of the idiopathic fetuses had “histologic features of a lysosomal storage disease…but specific enzymatic defect could not be proved”
Kooper 2006	Netherlands	75	“Presence of excessive fluid in more than one body cavity”	Not specified	Gaucher disease GM1-gangliosidosis Mucopolysaccharidosis I Mucopolysaccharidosis VII Niemann-Pick A/B Sialidosis	Both	Postnatal	4 definite cases and 2 probable cases of LSD. This study evaluated reference values of lysosomal enzymes in NIHF.
Gort 2012	Spain	30	“Excessive fluid accumulation in more than one foetal compartments and body cavities”	Amniocentesis, “LSD were investigated in all”	Gaucher disease GM1-gangliosidosis Mucopolysaccharidosis VII	Both	Prenatal	Reference center for LSD
Moreno 2013	Brazil	53	“Presence of generalized subcutaneous edema with or without cavitary effusion or more than one cavity effusion (pleural, pericardial, or peritoneal) in the absence of subcutaneous edema”	Ultrasound, CBC, hemoglobin electrophoresis, TORCH titers, fetal echocardiogram, inborn errors of metabolism testing, karyotype, autopsy	Gaucher disease GM1-Gangliosidosis Infantile sialic acid storage disease Mucopolysaccharidosis I Mucopolysaccharidosis II Mucopolysaccharidosis IVa Mucopolysaccharidosis VII Mucolipidosis II Niemann-Pick A/B Sialidosis	Both	Both	Reference center
Hasnani-Samnani 2013	Qatar	64	“Signs suggesting NIHF”	Ultrasound, CBC, thalassemia screening, Kleihauer-Betke, TORCH titers, Parvovirus B19, fetal echocardiogram, MCA PSV, karyotype	“Metabolic investigation…was done for only a few cases and was negative”	Not specified	Both
Ng 2013	Singapore	29	“Excessive fluid accumulation within at least two fetal extravascular compartments or body cavities”	CBC, thalassemia screening, Parvovirus B19, Toxoplasmosis, CMV, karyotype	Not specified	Not specified	Both	Reference center
Sheth 2016	India	33	“Accumulation of excess pathological fluid in fetal soft tissues and serous cavities detected by ultrasonography where isoimmunization has been excluded”	Ultrasound, CBC TORCH titers, CVS, amniocentesis, lysosomal enzyme testing, karyotype	Gaucher disease GM1-Gangliosidosis Infantile sialic acid storage disease Mucopolysaccharidosis I Mucopolysaccharidosis IVA Mucopolysaccharidosis VII Niemann-Pick A/B	Enzymatic	Both	Reference center
Vianey-Saban 2016	France	1700	Not specified	Not specified	Investigated amniotic fluid samples “for lysosomal storage disorders after exclusion of the most frequent etiologies of non-immune HF”	Enzymatic	Postnatal
Sudrie-Arnaud 2018	France	46	“Generalized fetal subcutaneous edema with or without effusions within body cavities, […] polyhydramnios associated with another fetal abnormality, or effusions for which no etiology had been found”	Karyotype, complete autopsy, inborn errors of metabolism testing	“Targeted capture sequencing panel that included 41 inborn errors of metabolism genes known to be associated with hydrops fetalis, ascites, or polyhydramnios with another fetal abnormality”	Molecular	Both	Initial 40 cases were retrospectively analyzed, followed by 6 additional prospective samples
Bruwer 2018	Oman	12	“Excess fluid accumulation in at least two serous cavities (abdomen/pleura/pericardium)	Ultrasound, hemoglobin electrophoresis, TORCH titers, fetal echocardiogram, lysosomal enzyme testing, karyotype	Gaucher disease Galactosialidosis GM1-Gangliosidosis GM2-Gangliosidosis Mucopolysaccharidosis I Mucopolysaccharidosis II Mucopolysaccharidosis IVA Mucopolysaccharidosis VII Mucolipidosis II Mucolipidosis III Niemann-Pick A/C Schindler disease Sialidosis Fucosidosis α-mannosidosis β-mannosidosis Multiple sulfatase deficiency	Both	Prenatal	Reference center
Al-Kouatly 2020 †	USA	126	“The presence of any of the following phrases in the patient chart: ‘hydrops,’ ‘born with hydrops,’ ‘fetal hydrops,’ ‘hydropic newborn,’ ‘hydrops in utero,’ ‘hydrops detected prenatally,’ ‘hydrops at birth,’ ‘hydrops fetalis’ ‘non-immune hydrops,’ and ‘non immune hydrops fetalis.’”	Not specified	Galactosialidosis Gaucher disease GM1-Gangliosidosis Infantile sialic acid storage disease Mucolipidosis II/III Mucopolysaccharidosis I Mucopolysaccharidosis VII Niemann-Pick A/B/C Sialidosis	Enzymatic	Both	Reference center
Total Cases		2,678

Abbreviations: CBC, complete blood count; CMV, cytomegalovirus; CVS, chorionic villus sampling; MCA PSV, middle cerebral artery peak systolic velocity; RPR, rapid plasma reagin; TORCH, toxoplasma, rubella, cytomegalovirus, herpes; HF hydrops fetalis

^†The study by Al-Kouatly et al., 2020 had 126 total cases of NIHF from January 2006 to December 2018. In that study, there were 28 LSD-positive NIHF cases from January 2006 to December 2018 and 98 LSD-negative NIHF controls from January 2015 to December 2018. The entire cohort of 28 LSD cases from January 2006 to December 2018 was used to determine the spectrum of LSD in NIHF. However, only the cohort from January 2015 to December 2018 was used to calculate the incidence of LSD in NIHF. There were 13 LSD-positive NIHF cases and 98 LSD-negative controls from January 2015 to December 2018.

In total, 2,678 cases of NIHF were identified across all studies (Table 1). After standard workup for NIHF per the authors’ institution, 80.8% (2,151/2,663) of cases did not receive a definitive diagnosis. With LSD testing, 177 cases of the total 2,663 cases (6.6%) were attributed to LSD (Table 2), leaving a total of 1,974 cases with an idiopathic cause (74.1%). Of the cases initially diagnosed as idiopathic, 8.2% were attributed to LSD (177/2,151). Six studies reported an extensive workup for LSD. ^{3,4,24,28–30} Among these six studies, 6.8% of cases were diagnosed with an LSD as the cause of NIHF (133/1,955).

Table 2.

Lysosomal Storage Disorder (LSD) cases reported in the case series of Nonimmune Hydrops Fetalis (NIHF)

Author/year	Total NIHF cases	Total cases with known diagnosis (excluding LSD)	Total idiopathic cases	Total LSD cases	Specific LSD type (n)
Mahony 1984	27	22 (81.5%)	4 (14.8%)	1 (3.7%)	Mucopolysaccharidosis (1)
Im 1984	20	12 (60.0%)	5 (25.0%)	3 (15%)	Gaucher disease (3)
McFadden 1989	90	70 (77.8%)	16 (17.8%)	4 (4.4%)	Mucopolysaccharidosis (2) Gaucher disease (1) Sialidosis (1)
McCoy 1995	82	62 (75.6%)	18 (22.0%)	2 (2.4%)	Gaucher disease (1) Niemann-Pick C disease (1)
Rejjal 1996	17	6 (35.3%)	9 (52.9%)	2 (11.8%)	GM1 gangliosidosis (1) Mucopolysaccharidosis (1)
Piraud 1996	54	0 (0%)	44 (81.5%)	10 (18.5%)	Galactosialidosis (2) GM1 gangliosidosis (2) Mucopolysaccharidosis VII (2) Sialidosis (2) Gaucher disease (1) Infantile sialic acid storage disease (1)
Groener 1999	17	7 (41.2%)	9 (52.9%)	1 (5.9%)	Mucopolysaccharidosis VII (1)
Has 2001	30	27 (90.0%)	3 (10.0%)	0 (0%)	N/A
Mascaretti 2003	29	20 (69.0%)	8 (27.6%)	1 (3.4%)	GM1 gangliosidosis (1)
Burin 2004	33	16 (48.5%)	12 (36.4%)	5 (15.1%)	Galactosialidosis (1) Mucolipidosis (1) Mucopolysaccharidosis IVA (1) Niemann-Pick A disease (1) Sialidosis (1)
Farve 2004	79	60 (75.9%)	12 (15.2%)	7 (8.9%)	Mucopolysaccharidosis VII (3) Niemann-Pick C disease (2) Sialidosis (2)
Rodriguez 2005	32	30 (93.8%)	2 (6.3%)	0 (0%)	N/A
Kooper 2006	75	71 (94.7%)	0 (0%)	4 (5.3%)	Mucopolysaccharidosis VII (2) Galactosialidosis (1) GM1 gangliosidosis (1)
Gort 2012	30	0 (0%)	28 (93.3%)	2 (6.7%)	Gaucher disease (1) Mucopolysaccharidosis VII (1)
Moreno 2013	53	43 (81.1%)	7 (13.2%)	3 (5.7%)	GM1 gangliosidosis (2) Infantile sialic acid storage disease (1)
Hasnani-Samnani 2013	64	37 (57.8%)	27 (42.2%)	0 (0%)	N/A
Ng 2013	29	20 (69.0%)	9 (31.0%)	0 (0%)	N/A
Sheth 2016	33	0 (0%)	26 (78.8%)	7 (21.1%)	Gaucher disease (1) Mucolipidosis (1) Mucopolysaccharidosis I (2) Mucopolysaccharidosis VII (2) Niemann-Pick A/B disease (1)
Vianey-Saban 2016	1700	0 (0%)	1593 (93.7%)	107 (6.3%)	Mucopolysaccharidosis VII (29) Infantile sialic acid storage disease (18) Galactosialidosis (12) GM1 gangliosidosis (12) Sialidosis (12) Gaucher disease (10) Mucolipidosis (6) Niemann-Pick C disease (4) Mucopolysaccharidosis IVA (3) Wolman disease (1)
Sudrie-Arnaud 2018 †	46	2 (4.3%)	41 (89.1%)	3 (6.5%)	Gaucher disease (1) GM1 gangliosidosis (1) Niemann-Pick C disease (1)
Bruwer 2018	12	7 (58.3%)	3 (25.0%)	2 (16.7%)	Galactosialidosis (2)
Al-Kouatly 2020 †	111	0 (0%)	98 (88.3%)	13 (11.7%)	Galactosialidosis (4) Mucopolysaccharidosis VII (4) Gaucher disease (2) Infantile sialic acid storage disease (2) Mucolipidosis (1)
Total Percent	2,663	512 19.2%	1,974 74.1%	177 6.6%

^†The study by Sudrie-Arnaud et al., 2018, had 1 case each of Barth syndrome and HNF1B. Since these are inborn errors of metabolism and not LSD, they were thus excluded from this review.

^‡The study by Al-Kouatly et al., 2020 had 126 total cases of NIHF from January 2006 to December 2018. In that study, there were 28 LSD-positive NIHF cases from January 2006 to December 2018 and 98 LSD-negative NIHF controls from January 2015 to December 2018. Consequently, only the cohort from January 2015 to December 2018 was used to calculate the incidence of LSD in NIHF. There were 13 LSD-positive NIHF cases and 98 LSD-negative controls from January 2015 to December 2018.

LSD diagnosis by enzyme analysis alone was done in 8/22 studies, both enzyme and molecular in 4/22, molecular alone in 2/22, and not specified in 8/22 studies. Only 9 LSD cases had the variant specified (Supplementary Table 1).

Table 3 reports the frequency of the different LSD that were commonly diagnosed in the 22 studies. The most common LSD identified were mucopolysaccharidosis VII (23.4%, 45/192), galactosialidosis (13.5%, 26/192), infantile sialic acid storage disease (13.0%, 25/192), Gaucher disease (12.0%, 23/192), GM1 gangliosidosis (11.5%, 22/192), and sialidosis (10.4%, 20/192). In total, 12 different LSD were identified as causes for NIHF across all studies. Of the 12 LSD identified in our review, 6 (50%) have approved therapies, while 8 (66.7%) have potential therapies currently being explored (Table 5).

Table 3.

Frequency of Lysosomal Storage Disorder Types in our Review

Lysosomal Storage Disorder	Cases†
Mucopolysaccharidosis  Type VII  Type IVA  Type unspecified  Type I	55 (28.6%) 45 4 4 2
Galactosialidosis	26 (13.5%)
Infantile sialic acid storage disease	25 (13.0%)
Gaucher disease	23 (12.0%)
GM1 gangliosidosis	22 (11.5%)
Sialidosis	20 (10.4%)
Niemann-Pick disease  C disease  A/B disease	11 (5.7%) 9 2
Mucolipidosis	9 (4.7%)
Wolman disease	1 (0.5%)
Total	192

^†In addition to the 177 LSD cases in Table 2, this table includes the 15 LSD-positive NIHF cases from Al-Kouatly et al., 2020, from January 2006 to January 2015.

Table 5.

Therapy for types of Lysosomal Storage Disorders identified in our study

Lysosomal Storage Disorder	Available therapies1	Potential therapies in Clinical Trials†
Gaucher	ERT and SRT (types I, II and III), none (perinatal lethal form)	Stem Cell Transplant and Gene Therapy in children and adults
Galactosialidosis	Symptomatic and supportive therapy	None
GM1 gangliosidosis	Symptomatic and supportive therapy	Stem Cell Transplant and Gene Therapy in children and adults
Infantile sialic acid storage disease	Symptomatic and supportive therapy	None
Mucolipidosis II/III	Symptomatic and supportive therapy	None
Mucopolysaccharidosis type VII	ERT	ERT, Stem Cell Transplant in children and adults
Mucopolysaccharidosis type IVA	ERT	ERT in children and adults
Mucopolysaccharidosis type I	ERT, HSCT	SRT in adults
Niemann-Pick disease type A/B	Symptomatic and supportive therapy	ERT in children and adults, SRT in adults
Niemann-Pick disease type C	SRT	2-Hydroxypropyl-beta-cyclodextrin
Sialidosis	Symptomatic and supportive therapy	None
Wolman disease	ERT	Stem Cell Transplant in adults

ERT, enzyme replacement therapy; HSCT, hematopoietic stem cell transplant; SRT, substrate reduction therapy.

¹Platt FM, d’Azzo A, Davidson BL, Neufeld EF, Tifft CJ. Lysosomal storage diseases. Nat Rev Dis Primers. 2018 Oct 1;4(1):27.

^†ClinicalTrials.gov accessed on 7/23/2020

Discussion

In 2014, our group performed a comprehensive literature review to evaluate the significance of LSD as the underlying etiology of NIHF.¹⁰ Since then, LSD testing has become more common as part of the workup for NIHF and several additional large case series have been published necessitating a re-examination of the literature.

In our review, 81% of cases where the initial NIHF standard-of care workup did not reveal an etiology, testing for LSD resulted in a diagnosis in 8.2% of cases (Table 2). This is likely an underestimation, as not all LSD were tested for in all of these studies. Also, many studies did not list every disease or enzyme tested. However, we know that up to 14 LSD have been associated with NIHF (Table 4).³¹ Six studies in this review performed comprehensive evaluation for LSD. ^{3,4,24,28–30} In these studies, the laboratories used either amniotic fluid supernatant or amniocytes prenatally, or plasma, leukocytes or fibroblasts (in the postnatal period) to measure enzymatic activity. Table 4 shows the enzymatic correlation to specific diseases. Of note, these studies with comprehensive evaluation of LSD were performed in national reference centers for LSD, likely because patients were sent to these referral centers specifically to evaluate for LSD. As would be expected, the more comprehensive the LSD workup, the higher the likelihood of reaching a diagnosis. Some LSD previously associated with NIHF were not detected in our literature review, because these were described in isolated case reports, and not in series with five or more cases of NIHF. However, our goal in restricting our systematic review to publications with at least five cases of NIHF was to diminish the risk of ascertainment bias.

Table 4.

Defect associated with most commonly diagnosed Lysosomal Storage Disorders in cases of Nonimmune Hydrops Fetalis

Lysosomal Storage Disorder	Protein Defect
Farber disease	Acid ceramidase
Gaucher disease	Glucocerebrosidase
GM1 gangliosidosis	β-galactosidase
Galactosialidosis	Protective protein / cathepsin A
Infantile sialic acid storage disease	Sialin transporter
Niemann-Pick disease type A/B	Sphingomyelinase
Niemann-Pick disease type C	NPC1, NPC2
Mucolipidosis II/III	GlcNAc-1-phosphotransferase
Mucopolysaccharidosis type I	α-L iduronidase
Mucopolysaccharidosis type IVa	N-acetylgalactosamine-6-sulfatase
Mucopolysaccharidosis type VII	β-glucuronidase
Multiple sulfatase deficiency	Sulfatase-modifying factor I
Sialidosis	Sialidase / neuraminidase 1
Wolman disease	Acid lipase

In our review of all case series examining NIHF, we found that the most commonly diagnosed LSD were mucopolysaccharidosis type VII, galactosialidosis, infantile sialic acid storage disease, Gaucher disease, and GM1 gangliosidosis among 192 LSD cases with NIHF (Table 3). These five LSD accounted for greater than 70% of LSD cases diagnosed in our review. This differed from our initial review of the literature in 2014 with only 35 LSD cases, where more than 70% were caused by mucopolysaccharidosis type VII, Gaucher disease, GM1 gangliosidosis, sialidosis, and mucopolysaccharidosis type not specified. Another striking difference from our first review was the frequency of idiopathic causes of NIHF. In that review, we had included 678 total cases of NIHF, 35 with LSD, and only 24.5% had an idiopathic cause. Currently, out of 2,663 total NIHF cases, 177 with LSD, 74% were found to have an idiopathic cause. This finding is largely attributable to the study by Vianey-Saban et al.²⁸ which had an idiopathic rate of nearly 94% out of 1700 cases, representing more than 65% of the total cases in our current review. Excluding this study, still 40% of NIHF cases have an idiopathic cause across the remaining 21 studies.

Of the five most common LSD associated with NIHF in our review, two have approved therapies: mucopolysaccharidosis type VII and Gaucher disease (Table 5). Gene therapy is currently being examined as a potential treatment for GM1 gangliosidosis. The fact that approximately 50% of NIHF cases caused by these five most common LSD could be treated underscores the need to include LSD testing as part of the workup for NIHF. Further research is needed to evaluate the effectiveness of in-utero or postnatal treatment of NIHF due to LSD.

Given that LSD was diagnosed in 8% of “idiopathic” NIHF cases, comprehensive LSD testing should be routine when standard-of-care workup is negative for fetal hydrops. Therefore, we suggest at least a two-step approach. First, common causes of NIHF should be evaluated as suggested in the clinical guidelines published in 2015 by the Society for Maternal Fetal Medicine.² Subsequently, for cases that remain idiopathic after initial NIHF workup, testing for LSD should be done. Prenatal LSD testing not only provides diagnosis, but also allows the option for pregnancy termination, appropriate postnatal management and planning for possible early intervention. Moreover, their detection may aid in prenatal diagnosis in subsequent pregnancies because many of the LSD associated with NIHF have an autosomal recessive mode of inheritance. Our recent systematic review of monogenic causes of NIHF cataloged 131 genes with strong molecular evidence for an association with NIHF and 46 genes with emerging molecular evidence for an association with NIHF.³¹ The most common monogenic category for NIHF with strong molecular evidence and emerging molecular evidence was metabolic disorders, of which LSD comprised the majority.

Prenatal LSD diagnosis can be performed on cells obtained by chorionic villus sampling or amniocentesis. Table 4 lists the enzymes of inborn errors of metabolism associated with NIHF. We recommend prenatal LSD evaluation with either a comprehensive LSD enzyme testing or LSD gene panels at specialized laboratories. Molecular prenatal diagnosis of all LSD can be done in specialized laboratories. Knowledge of the variant in the proband or in the heterozygous parents allows the use of variant analysis for prenatal diagnosis. Variant analysis is recommended as a confirmatory assay, is more accurate for prenatal diagnosis in a future pregnancy, and can aid pre-implantation genetic diagnosis. Further research on the molecular etiology among the most common LSD is needed to investigate whether particular pathogenic variants account for recurrent NIHF.

The most obvious shortcoming of our study is the fact that a review such as ours can only be as reliable as the published cases. There is certainly substantial ascertainment bias in the literature. Therefore, we excluded manuscripts with less than five cases of NIHF, in an effort to minimize publication bias. To establish the true incidence of LSD in NIHF, idiopathic cases after the standard-of-care workup should be tested for all LSD that have been associated with NIHF (Table 4). Unfortunately, across the 22 studies included in our review, there was a wide variation in the number of LSD tested for, with most of the studies not testing for all of the LSD associated with NIHF.

There are four prior reviews of NIHF case series in the literature, including our own published in 2014. Bellini et al. compiled a very thorough review of cases and classifications of the etiologies of NIHF, but did not delve into the workup, and did not examine the prevalence of LSD as a cause.³² Jauniaux et al. wrote a large review paper of 600 cases of NIHF, but his study was also limited by the fact that all included cases of LSD derived from case reports.³³ Machin’s review from 1989 had the most extensive list of cases of any prior study on NIHF (1,414) but was limited because almost half of those cases originated from case reports.⁸ Our current study represents the most comprehensive systematic review of the workup and available treatments of NIHF for LSD to date, including more than 2,600 NIHF reported cases.

Take-home message:

Comprehensive LSD testing should be routine when standard-of-care workup is negative for nonimmune hydrops fetalis.

Data availability statement:

The data that support the findings of this study are available from the corresponding author upon reasonable request.