Background
Fabry disease (OMIM 301,500, FD) is an X-linked lysosomal storage disorder (LSD) caused by mutations in the
GLA gene leading to deficient α-galactosidase A (α-Gal A) activity. This enzyme deficiency results in an accumulation of globotriaosylceramide (GL-3) and globotriaosylsphingosine (deacylated form of GL-3, lyso-GL-3) [
1]. Phenotypes vary from the “classic” phenotype, with pediatric onset and multiorgan involvement, to “nonclassical” later onset, a predominantly cardiac phenotype. Young patients may initially experience pain, hypohidrosis and gastrointestinal symptoms. Other manifestations of FD, such as renal and cardiac disease, manifest later in adolescence or adulthood [
2]. Newborn screening identified a surprisingly high frequency of males with FD (~ 1 in 1,250) [
3].
Currently, numerous
GLA mutations are reported in gene mutation databases [
4]. Enzyme replacement therapy (ERT) and adjunctive treatments can provide significant clinical benefit [
5]. Early treatment before the onset of potentially irreversible vital organ pathology is ideal. Asymptomatic children with
GLA mutations should be followed closely for the development of signs, symptoms, or laboratory changes, which would warrant treatment initiation [
6]. A comprehensive care plan should be implemented to guide the management of children with FD.
Although FD has been known for more than a century, this LSD remains poorly recognized, especially in children in China. A typical patient’s odyssey means multiple visits to more than ten different medical specialists before the child achieves a confirmatory diagnosis of FD. On average, this process comes 14–16 years following the onset of the first symptoms [
7]. Considering the diversity and “nonspecific” clinical manifestations accompanying with life-threatening aspects of FD, methods to improve effective screening and management of suspect cases are needed.
Testing from dried blood spots (DBSs) is now possible for LSDs, making population screening technically feasible. α-Gal A and lyso-GL-3 analysis and
GLA sequencing in DBS for the diagnosis of FD were evaluated [
8]. α-Gal A activity testing is diagnostic for male patients. However, confirmation of the disease-causing
GLA mutation is important to help establish the disease phenotype. In female patients, as α-Gal A activity is often found within the normal range, testing consisting of plasma or DBS lyso-GL-3 analysis and
GLA sequencing provides the greatest sensitivity and specificity [
9]. In addition, due to the multiple organ systems affected by FD and the complexity of disease management, it is recommended that multidisciplinary teams (MDTs) be established wherever possible to oversee the management of pediatric patients with FD [
5]. The aim of this study was to explore how an effective multidisciplinary perspective and DBS triple-testing (alpha-Gal A, Lyso-GL-3,
GLA gene) could be used for screening and management of children with FD at a tertiary children’s hospital in China.
Discussion
In this study, based on a defined screening protocol (DBS triple-test for children with a high-risk profile of FD and newborn screening by genetic testing) and a multidisciplinary approach, we newly diagnosed 7 children, including 2 neonates, with FD in the hospital in the last twelve months accompanied by 3 referred FD children from other hospitals. No case was diagnosed with FD before the establishment of the MDT approach. Five children were diagnosed with FD in a timely manner by high-risk profile and DBS triple-test screening, with a yield of diagnosis of 14.3%. After MDT evaluation, four of them started to receive ERT, and the accumulation of lyso-GL-3 in the blood was significantly improved, which could delay vital organ pathology and disease progression.
From a historical point of view, the first teams that began patient care using a multidisciplinary approach were oncologists. It is now a widely held view that the treatment of most cancers has benefitted from this integrated MDT approach, and patient satisfaction and efficiency are improved [
13]. FD is considered a rare disease. The diagnosis is challenging due to variability and complexity in the presentation and the chronic, slowly progressive nature of FD. It is recognized that there are many individuals affected who are unscreened and undiagnosed. A multidisciplinary approach is advocated to screen, diagnose, care for, and manage patients with FDs, and the United States-based perspective also recommends multidisciplinary clinical teams to oversee the management of FD in children [
5]. Since FD remains poorly recognized in children in China and no case had been diagnosed in our hospital before, it was urgent to set up the MDT for pediatric FD in the hospital, which included the screening team who focused on high-risk profiles and the management team who focused on the diagnosis, treatment, and follow-up. To make more staff aware of this disease, continuous education was given not only to MDT members but also to others from associated departments.
A longitudinal study from Italy that screened ~ 17,000 individuals with clinical manifestations suggestive of FD showed that 100% of males with classic FD had α-Gal A enzymatic activity below the normal reference range, in contrast to only 46% of females harbouring the same pathogenic variants [
4]. A similar result was demonstrated in a United States study that showed that α-Gal A activity in DBS had high sensitivity but lower specificity for FD in males, as not all males with low α-Gal A activities were confirmed to have FD [
12]. Therefore, using
GLA sequencing and Lyso-GL-3 detection was useful for disease confirmation in males. For females, they found that first-tier testing consisting of
GLA sequencing and Lyso-GL-3 analysis provided the greatest sensitivity and specificity, whereas enzyme testing had lower sensitivity and was therefore less useful as a first-tier test [
9]. Accordingly, we set up the DBS triple-test (α-Gal A, Lyso-GL-3,
GLA gene) screening approach using sex-specific algorithms. For boys, a level of α-Gal A determined by MS/MS below normal was followed by Sanger sequencing of the
GLA gene and the level of lyso-GL-3 tested by MS/MS. For girls, a level of lyso-GL-3 tested by MS/MS above normal was followed by Sanger sequencing of the
GLA gene, and the level of α-Gal A was determined by MS/MS. Sex-specific detection algorithms might prioritize tests with high specificity and sensitivity that offer an effective way to identify individuals with FD.
Of course, children with FD may initially experience pain, hypohidrosis, and gastrointestinal symptoms, while renal and cardiac disease may present later in adolescence or adulthood [
2]. A hallmark sign of classic FD in children is neuropathic pain in the hands and feet, most commonly in the palms, soles and fingertips. This symptom was reported by up to 72.3% of patients with FD and is more frequently present in boys [
5]. The mean age of onset of pain was reported as 10 years in boys and 15 years in heterozygous girls [
5]. In this study, thirty-five high-risk children were referred for screening, with a yield of diagnosis of 14.3% (5/35). Among these 5 diagnosed children, four had neuropathic pain. One of them had pain accompanied by abnormal liver function. Although abnormal liver function was unexpected in FD, previous study showed that liver biopsy from a longstanding FD patient with abnormal liver function indicated the accumulation of GL-3 in liver [
14]. Whether the abnormal liver function is related to the deposition of GL-3 and lyso-GL-3, or is caused by other reasons, further follow-up and more cases are needed to clarify this issue. In addition, the other diagnosed child with FD in this study was screened due to a high-risk profile of unexplained renal tubular dysfunction. In FD patients, renal involvement is caused by the accumulation of GL-3 and Lyso-GL-3 in all renal cell types, including podocytes, endothelial cells, mesangial cells and tubular cells [
15,
16]. Although less common as tubular dysfunction, manifestations include Fanconi syndrome, distal renal tubular acidosis, and isosthenuria [
15,
17]. Tubular damage and dysfunction may be accompanied by the excretion of tubular lesion markers, such as α1-microglobulin and retinol-binding protein [
15].
In FD, based on enzymatic assays for α-Gal A activity, previous newborn screening studies revealed frequencies of the classic and later-onset phenotypes of up to 1 in 22,570 males and 1 in 1,390 males, respectively [
3]. It allows for the identification and monitoring of individuals with FD from an early age and identifies affected adults in the family. Such programs have been initiated in some states in the United States [
18] and several European countries [
19,
20]. In this study, we enrolled newborns who were at risk of genetic metabolic disorders undergoing genetic testing in the hospital, and the
GLA gene was listed as a routine analysis gene. Two neonates were detected early with
GLA mutations in the 12-month period, with a yield of detection of 0.14% (2/1420). This newborn screening approach needs further evaluation and cost-effectiveness analysis to identify its feasibility and value. Newborn screening raises challenges in defining the most appropriate way to counsel families of infants diagnosed with FD and how to effectively monitor and manage those infants to optimize clinical outcomes [
21]. Although the use of newborn screening for the identification of FD remains an ethical issue, previous studies indicate that most patients prefer to be informed [
21]. Furthermore, families with known FD can be offered preimplantation genetic diagnosis (PGD) of embryos prior to implantation during assisted reproduction.
In addition, ERT, adjunctive treatments, and regular follow-up can provide significant clinical benefit. There is strong circumstantial evidence and increasing clinical recognition of the crucial importance of early treatment initiation to mitigate the long-term impact of the disease [
22]. The management of FD requires a coordinated, multidisciplinary care approach. Asymptomatic children should be followed closely for the development of renal, cardiac, neurological, or gastrointestinal signs, symptoms, or laboratory changes, which would warrant treatment initiation [
6]. A previous study indicated that after 65 months of treatment with a 1 mg/kg agalsidase dose every other week, patients had substantial clearance of podocyte GL-3 inclusions [
23]. The greatest clearance was observed in the youngest patient treated, beginning at age 7 years. ERT treatment during childhood may positively impact school attendance, exercise performance, energy levels, and pain, with subsequent improvements in quality of life, and early treatment before the onset of potentially irreversible vital organ pathology is ideal.
Some limitations of our study need to be acknowledged. First, this multidisciplinary approach to the screening and management of children with FD was only implemented in the last twelve months. Second, in this study, we used the DBS triple-test screening approach with sex-specific algorithms, but the sensitivity and specificity of this method were not verified in our population. Third, although missense and nonsense variants account for the majority of disease-causing mutations in FD, Sanger sequencing of the GLA gene could not detect insertions, deletions, and structural rearrangements.
In conclusion, early diagnosis of patients with FD is vital. A year after establishing an MDT for pediatric FD, this program met its goals. Screening and management of children with FD was effective based on a defined screening protocol and a multidisciplinary approach. We should pay more attention to the high-risk profiles of pain, angiokeratoma, decreased sweating, and unexplained chronic kidney disease in children. In this sense, this model could be extended to other regions in China.
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