Twelve-year review of galactosemia newborn screening in Taiwan: Evolving methods and insights

Background

Galactosemia was introduced into Taiwan's routine newborn screening (NBS) program in 1985. This study presents a 12-year experience, emphasizing disease diagnosis and screening performance.

Method

NBS for galactosemia utilized dried blood spot samples taken 48-72 h post-delivery, with total galactose (TGal) level as the primary marker. Newborns with critical TGal levels were referred immediately, while those with borderline TGal underwent a recall test. GALT activity measurement was applied simultaneously as the second-tier marker. Further confirmatory tests, such as whole exome sequencing (WES), were conducted upon referral.

Results

From January 1st, 2011, to December 31st, 2022, 51 cases were identified from 817,906 newborns. Of these, nine individuals had persistently elevated TGal. Diagnoses included one case of GALT deficiency, one of GALM deficiency, and seven of GALE deficiencies. Notably, the classic galactosemia patient (GALT deficiency) presented with extreme high TGal and was referred to the hospital for diet management immediately. All affected patients were instructed to adopt a galactose-restricted diet. By the median age of 2.5 years, all exhibited normal development and liver function.

Conclusion

The incidence of classical galactosemia and its variants is extremely low in Taiwan. Incorporating WES into NBS has improved our ability to detect various galactosemia forms, enriching our understanding of the genetic underpinnings. While these newly discovered forms often present with milder initial elevations in TGal, specific biochemical investigations and regular monitoring are essential to understanding the long-term implications and outcomes.

Late-onset symptomatic hyperprolactinemia in 6-pyruvoyl-tetrahydropterin synthase deficiency

BACKGROUND

Tetrahydrobiopterin (BH4) deficiency caused by 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is a rare disorder that is one of the major causes of hyperphenylalaninemia in Taiwan.

METHODS

In this study, we reviewed the clinical courses of 12 adolescent and adult patients (7 females and 5 males) with PTPS deficiency.

RESULTS

The patients were treated shortly after diagnosis through newborn screening with a combination of BH4, levodopa/carbidopa, and 5-OH-tryptophan. Their plasma phenylalanine and tyrosine levels were well controlled, and their prolactin levels were also decreased after treatment. However, their prolactin levels gradually rose as they grew into puberty, and at a current age of 27.5 [interquartile range (IQR 7.9)] years, five of the 12 patients had either highly elevated prolactin levels (> 100 ng/mL in one male patient, normal reference values, male < 11 ng/mL, female < 17 ng/mL) or symptoms, including irregular menstruation, amenorrhea, and breast swelling (in four female patients). The dosage of levodopa in these five patients (14.3 (IQR 3.0) mg/kg/day) was slightly higher than that in the other patients (p = 0.05). Magnetic resonance imaging studies did not reveal an increase in the size of the anterior pituitary gland, although a Rathke cleft cyst was found in one patient. Two patients received cabergoline treatment, which promptly lowered prolactin levels and relieved symptoms.

CONCLUSIONS

Hyperprolactinemia is common in female patients with PTPS deficiency, especially after puberty. A long-acting dopamine agonist, such as cabergoline, may be a necessary adjunctive treatment for most patients with BH4 deficiency.

Utility of whole-exome sequencing for patients with multiple congenital anomalies with or without intellectual disability/developmental delay in East Asia population

BACKGROUND

Congenital anomalies (CAs) with or without intellectual disability (ID)/developmental delay (DD) comprise a heterogeneous spectrum of diseases that affect approximately 3% of live births worldwide. Recently, whole-exome sequencing (WES) demonstrated the highly heterogeneous genetic causes of CAs. The purpose of this study was to evaluate a referral system to increase the yield of WES for CAs.

METHODS

From August 2018 to July 2019, patients with CAs, with or without ID/DD, after excluding gross chromosomal aberrations, were referred to geneticists in two medical centers. Variant prioritization was conducted with an AI-assisted tool for whole exomes or a CA-related gene panel.

RESULTS

Forty patients (27 males and 13 females) with CAs were enrolled in the study with a mean age of 4.71 years (range, 0.01-18.2). Pathogenic variants in 14 genes were discovered in 16 patients (three patients with CHD7 and 13 patients with one gene each of ATP6V1B2, TAF6, COL4A3BP, ANKH, BMP2, SMARCA4, CUL4B, PGAP3, SOX11, FBN2, PTPN11, SOS1, or PROKR2), with a positive diagnostic rate of 40%. Among the 16 positive cases, 13 (81%) also had ID/DD. The inheritance was autosomal dominant in 13 (81%), autosomal recessive in two (13%), and X-linked in one (6%). Only five patients received a correct clinical diagnosis before WES. The analyses of patients with a negative genetic diagnosis revealed a phenotype and gene mutation load similar to those of the positive-finding patients but with a lower percentage of ID/DD.

CONCLUSIONS

The careful selection of patients by experienced geneticists and the exclusion of chromosomal aberrations raises the positive rate of the molecular diagnosis for CAs to 40%. However, more than half of the patients with CAs still do not have a genetic diagnosis by current technologies.

Corneal Biomechanical Characteristics in Osteogenesis Imperfecta With Collagen Defect

Purpose

To identify the characteristic corneal biomechanical properties of osteogenesis imperfecta (OI), and to compare the corneal biomechanical properties between OI and keratoconus.

Methods

We included 46 eyes of 23 patients with OI, 188 eyes of 99 keratoconus patients, and 174 eyes of 92 normal controls to compare corneal biomechanical parameters between OI corneas, keratoconus, and normal controls by using Corneal Visualization Scheimpflug Technology (Corvis ST).

Results

Patients with OI had significantly higher Corvis biomechanical index (CBI) (P < 0.001), higher tomographic and biomechanical index (TBI) (P = 0.040), lower Corvis Biomechanical Factor (CBiF) (P = 0.034), and lower stiffness parameter at first applanation (SP-A1) (P < 0.001) compared with normal controls. In contrast, OI group showed lower CBI (P < 0.001), lower TBI (P < 0.001), higher CBiF (P < 0.001), and higher SP-A1 (P = 0.020) than keratoconus group. Notably, the stress-strain index (SSI) was not significantly different between the OI and normal controls (P = 1.000), whereas keratoconus showed the lowest SSI compared with OI group (P = 0.025) and normal controls (P < 0.001).

Conclusions

Although the corneal structures of OI patients are less stable and easier to deform as compared to those of the control group, there is no significant difference in material stiffness observed between the OI and normal controls. In contrast, the corneas of keratoconus showed not only lower structural stability and higher deformability but also lower material stiffness compared with those of OI cornea and normal controls.

Translational Relevance

The biomechanical alterations are different between OI corneas and keratoconus.

High incidence of null variants identified from newborn screening of X-linked adrenoleukodystrophy in Taiwan

Background

Adrenoleukodystrophy (ALD) is an X-linked peroxisomal disorder caused by variants in the ABCD1 gene and can lead to Addison disease, childhood cerebral ALD, or adrenomyeloneuropathy. Presymptomatic hematopoietic stem cell transplantation is the only curative treatment for the disease and requires early detection through newborn screening (NBS) and close follow-up.

Methods

An NBS program for ALD was performed by a two-tiered dried blood spot (DBS) lysophosphatidylcholine C26:0 (C26:0-LPC) concentration analysis. ABCD1 sequencing was eventually added as a third-tier test, and whole exome sequencing was used to confirm the diagnosis of all peroxisomal diseases. Affected newborns were followed-up for adrenal insufficiency and cerebral white matter abnormalities.

Results

We identified 12 males and 10 females with ABCD1 variants, and 3 patients with Zellweger syndrome from 320,528 newborns. Eight (36.4%) ABCD1 variants identified in the current study were null variants, but there were no hotspots or founder effect. During a median follow-up period of 2.28 years, two (16.7%) male patients with ABCD1 variants developed Addison's disease. Extended family screening revealed one 28-year-old asymptomatic hemizygous father of a null variant (c.678delC). Among the three with Zellweger syndrome, one died at the age of 3 months, one showed developmental delay at the age of 1 year, and one was lost to follow-up.

Conclusion

Screening for ALD has been added to the NBS program in Taiwan with a high degree of success. The screening algorithm revealed a high proportion of null variants in cases found by NBS in Taiwan, a subset of patients who may have earlier disease onset. We also demonstrate the feasibility of combining the diagnosis of ALD and other peroxisomal disorders into one screening algorithm.

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We report our screening results of a successful newborn screening for adrenoleukodystrophy in Taiwan since November 2016.

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C26:0-LPC levels at newborn screening tended to be higher in males with null variants than those with missense variants.

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A higher proportion of ALD patients carry null variants in Taiwan,and may have earlier onset or more severe phenotypes.

Improved diagnosis of citrin deficiency by newborn screening using a molecular second-tier test

BACKGROUND

Citrin deficiency is an autosomal recessive disorder caused by variants of the SLC25A13 gene. Although newborn screening (NBS) provides an opportunity for its early diagnosis and treatment, citrin deficiency detection rates remain lower than those estimated.

METHODS

Before 2018, NBS for citrin deficiency was based on citrulline levels alone. In June 2018, a second-tier molecular test was implemented to detect 11 common variants of the SLC25A13 gene and improve the NBS detection rates. This study compares the incidence rates and costs before and after the second-tier implementation.

RESULTS

Prior to 2018, five subjects were diagnosed via NBS, and 12 of 555,449 newborns screened were missed. In comparison, 11 subjects were diagnosed out of 198,071 newborns screened after 2018, and there were no false-negatives. The citrin deficiency detection rate increased from 1/32,673 to 1/18,006 after the second-tier test was implemented, with only a minimal increase in the total cost. The number of false-positive in our cohort was tolerable. Subjects with citrin deficiency may present with borderline elevated citrulline levels; these can remain slightly elevated or increase considerably on retest. Four patients (80%) detected prior to second-tier testing and six patients (55%) detected after it was implemented were identified based on the citrulline levels alone. However, at the time of second blood sampling, the normal citrulline level of five subjects did not exclude a citrin deficiency diagnosis.

CONCLUSIONS

Our study shows that it is vital and cost-effective to employ second-tier molecular testing to improve the detection of citrin deficiency by NBS.

Asymptomatic ASS1 carriers with high blood citrulline levels

INTRODUCTION

Citrullinemia Type 1 (CTLN1) is an autosomal recessive disorder caused by variants in the ASS1 gene. This study intends to clarify the etiology of false positives in newborn screening for citrullinemia.

METHOD

Newborns who had elevated dried-blood spot citrulline levels were enrolled, and medical records were reviewed retrospectively. Common ASS1 variants were screened using high-resolution melting analysis.

RESULT

Between 2011 and 2021, 130 newborns received confirmatory testing for citrullinemia, 4 were found to be patients for CTLN1; 11 were patients with citrin deficiency; and 49 newborns were confirmed to be carrying one pathogenic ASS1 variant. The incidence of CTLN1 was 1 in 188,380 (95% confidence interval: 1 in 73,258 to 1 in 484,416). All ASS1 variants studied in this cohort were located in exons 11 to 15, which encode the tetrameric interface regions of the ASS1 protein. Among 10 ASS1 carriers with elevated citrulline levels and complete sequence data, four (40%) revealed additional non-benign ASS1 variants; in contrast, only 2 of the 26 controls (7.7%), with normal citrulline levels, had additional ASS1 variants.

CONCLUSION

Heterozygote ASS1 variants may lead to a mild elevation of blood citrulline levels: about 2-6 times the population mean. Molecular testing and family studies remain critical for precise diagnosis, genetic counseling, and management.

Diversity in heritable disorders of connective tissue at a single center

BACKGROUND

Heritable disorders of connective tissue (HDCT) is a heterogeneous group of conditions caused by defects in genes responsible for extracellular matrix elements. Although next-generation sequencing (NGS) technology can be used to analyze many genes at a time, precisely diagnosing HDCT is still challenging because of the overlapping phenotypes and genotypes.

METHODS

A 67-gene NGS targeted panel or whole-exome sequencing was employed for the diagnosis of HDCT over 4 years. Phenotypes and genotypes of patients were analyzed retrospectively.

RESULTS

Mutations in 16 genes were discovered in 34 patients with the suspicion of Ehlers-Danlos syndrome (n = 7), Marfan syndrome (n = 2), osteogenesis imperfecta (n = 3), skeletal dysplasia (n = 18), and others (n = 4). Eighteen patients were found to have mutations in collagen genes, three had SERPINF1 mutations, two had TRPV4 mutations, two had FBN1 mutations, two had COMP mutations, and mutations in seven other genes were found in one patient each. The eight patients with COL1A1 mutations had a wide variation in phenotype. Patients with COL3A1 and COL5A1 mutations presented with classic EDS, those with SERPINF1 mutations presented with typical OI type VI, those with TRPV4 mutations presented with severe spinal deformity, and those with COL2A1 mutations presented with syndromic or nonsyndromic bone dysplasia or only short stature.

CONCLUSION

A wide diversity in HDCT was observed. Therefore, knowledge about the phenotype-genotype correlation in HDCT is still crucial in the diagnosis of this group of diseases, and an improvement in the screening tool will be needed.

Genotypic and phenotypic correlations of biotinidase deficiency in the Chinese population

Biotinidase deficiency is an autosomal recessive disorder that affects the endogenous recycling and release of biotin from dietary protein. This disease was thought to be rare in East Asia. In this report, we delineate the phenotype of biotinidase deficiency in our cohort. The genotypes and phenotypes of patients diagnosed with biotinidase deficiency from a medical center were reviewed. The clinical manifestations, laboratory findings, and molecular test results were retrospectively analyzed. A total of 6 patients were evaluated. Three patients (50%) were diagnosed because of a clinical illness, and the other three (50%) were identified by newborn screening. In all patients, the molecular results confirmed the BTD mutation. The three patients with clinical manifestations had an onset of seizure at the age of 2 to 3 months. Two patients had respiratory problems (one with apnea under bilevel positive airway pressure (BiPAP) therapy at night, and the other with laryngomalacia). Hearing loss and eye problems were found in one patient. Interestingly, cutaneous manifestations including skin eczema, alopecia, and recurrent fungal infection were less commonly seen compared to cases in the literature. None of the patients identified by the newborn screening program developed symptoms. Our findings highlight differences in the genotype and phenotype compared with those in Western countries. Patients with biotinidase deficiency benefit from newborn screening programs for early detection and management.