Overview of common inherited metabolic diseases in a Southern Chinese population of Hong Kong

Recurrent rhabdomyolysis and glutaric aciduria type I: a case report and literature review

BACKGROUND

Glutaric acidemia type I (GA-I) is a rare metabolic disorder caused by mutation of the glutaryl- CoA dehydrogenase (GCDH) gene. The occurrence of rhabdomyolysis with GA-I is extremely rare.

METHODS

We reported a child with recurrent rhabdomyolysis and undiagnosed glutaric acidemia type I (GA-I). And a literature review was performed.

RESULTS

A 4.5-year-old girl was admitted to our hospital due to recurrent rhabdomyolysis for 3 times within three years. At the third admission, she was diagnosed with GA-I by biochemical testing and mutation analysis. The girl was found to have a serine to leucine replacement mutation of the GCDH gene in exon 8 at position 764. Other three patients with rhabdomyolysis and GA-I were discovered by literature searching.

CONCLUSIONS

This report highlights that patients with GA-I may have an increased risk of rhabdomyolysis.

Inherited metabolic diseases in the Southern Chinese population: spectrum of diseases and estimated incidence from recurrent mutations

Inherited metabolic diseases (IMDs) are a large group of rare genetic diseases. The spectrum and incidences of IMDs differ among populations, which has been well characterised in Caucasians but much less so in Chinese. In a setting of a University Hospital Metabolic Clinic in Hong Kong, over 100 patients with IMDs have been seen during a period of 13 years (from 1997 to 2010). The data were used to define the spectrum of diseases in the Southern Chinese population. Comparison with other populations revealed a unique spectrum of common IMDs. Furthermore, the incidence of the common IMDs was estimated by using population carrier frequencies of known recurrent mutations. Locally common diseases (their estimated incidence) include (1) glutaric aciduria type 1 (∼1/60,000), (2) multiple carboxylase deficiency (∼1/60,000), (3) primary carnitine deficiency (∼1/60,000), (4) carnitine-acylcarnitine translocase deficiency (∼1/60,000), (5) glutaric aciduria type 2 (∼1/22,500), (6) citrin deficiency (∼1/17,000), (7) tetrahydrobiopterin-deficient hyperphenylalaninaemia due to 6-pyruvoyl-tetrahydropterin synthase deficiency (∼1/60,000), (8) glycogen storage disease type 1 (∼1/150,000). In addition, ornithine carbamoyltransferase deficiency and X-linked adrenoleukodystrophy are common X-linked diseases. Findings of the disease spectrum and treatment outcome are summarised here which may be useful for clinical practice. In addition, data will also be useful for policy makers in planning of newborn screening programs and resource allocation.

Inborn errors of metabolism and expanded newborn screening: review and update

Inborn errors of metabolism (IEM) are a phenotypically and genetically heterogeneous group of disorders caused by a defect in a metabolic pathway, leading to malfunctioning metabolism and/or the accumulation of toxic intermediate metabolites. To date, more than 1000 different IEM have been identified. While individually rare, the cumulative incidence has been shown to be upwards of 1 in 800. Clinical presentations are protean, complicating diagnostic pathways. IEM are present in all ethnic groups and across every age. Some IEM are amenable to treatment, with promising outcomes. However, high clinical suspicion alone is not sufficient to reduce morbidities and mortalities. In the last decade, due to the advent of tandem mass spectrometry, expanded newborn screening (NBS) has become a mandatory public health strategy in most developed and developing countries. The technology allows inexpensive simultaneous detection of more than 30 different metabolic disorders in one single blood spot specimen at a cost of about USD 10 per baby, with commendable analytical accuracy and precision. The sensitivity and specificity of this method can be up to 99% and 99.995%, respectively, for most amino acid disorders, organic acidemias, and fatty acid oxidation defects. Cost-effectiveness studies have confirmed that the savings achieved through the use of expanded NBS programs are significantly greater than the costs of implementation. The adverse effects of false positive results are negligible in view of the economic health benefits generated by expanded NBS and these could be minimized through increased education, better communication, and improved technologies. Local screening agencies should be given the autonomy to develop their screening programs in order to keep pace with international advancements. The development of biochemical genetics is closely linked with expanded NBS. With ongoing advancements in nanotechnology and molecular genomics, the field of biochemical genetics is still expanding rapidly. The potential of tandem mass spectrometry is extending to cover more disorders. Indeed, the use of genetic markers in T-cell receptor excision circles for severe combined immunodeficiency is one promising example. NBS represents the highest volume of genetic testing. It is more than a test and it warrants systematic healthcare service delivery across the pre-analytical, analytical, and post-analytical phases. There should be a comprehensive reporting system entailing genetic counselling as well as short-term and long-term follow-up. It is essential to integrate existing clinical IEM services with the expanded NBS program to enable close communication between the laboratory, clinicians, and allied health parties. In this review, we will discuss the history of IEM, its clinical presentations in children and adult patients, and its incidence among different ethnicities; the history and recent expansion of NBS, its cost-effectiveness, associated pros and cons, and the ethical issues that can arise; the analytical aspects of tandem mass spectrometry and post-analytical perspectives regarding result interpretation.

Novel mutations in ETFDH gene in Chinese patients with riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency

BACKGROUND

Multiple acyl-CoA dehydrogenase deficiency (MADD, OMIM 231680) or glutaric aciduria type II (GAII) is an inherited autosomal recessive disease affecting fatty acid, amino acid and choline metabolism, due to mutations in one of three genes namely, electron transfer flavoprotein alpha-subunit, ETFA (OMIM 608053), electron transfer flavoprotein beta-subunit, ETFB (OMIM 130410) and electron transfer flavoprotein dehydrogenase, ETFDH (OMIM 231675). Some MADD patients are responsive to riboflavin treatment with an excellent prognosis. Recently, mutations in ETFDH were found to be responsible for all riboflavin-responsive MADD patients. In this study, we present the clinical features and molecular studies of 2 Chinese families with riboflavin-responsive MADD.

METHODS

Genomic DNA was extracted from peripheral blood samples or skin fibroblast cultures from the patients and normal controls. The thirteen exons of ETFDH were amplified by PCR. PCR products were sequenced in both forward and reverse directions. To rule out mutations in other genes, phenotype segregation was studied in the families by microsatellite markers in the proximity of the 3 genes, ETFA, ETFB and ETFDH.

RESULTS

Four novel mutations in ETFDH were detected in the 2 families. In family 1, a frame shift mutation, c.1355delG which introduced a premature-termination codon (PTC), I454X in exon 11 of ETFDH was found. Another mutation was a c.250G>A transition in exon 3 of ETFDH, A84T. In family 2, two novel missense mutations were identified, P137S, in exon 4 and G467R in exon 11. No carrier of these four mutations was identified from about 150 alleles of healthy Chinese control subjects.

CONCLUSIONS

Four novel mutations (3 missenses and 1 deletion) in ETFDH were found in Chinese families that presented with riboflavin-responsive MADD, which further expands the list of mutations found in patients with riboflavin-responsive MADD. Furthermore, we illustrated the utility of phenotype-genotype segregation in MADD families to prioritize genes for sequencing or to rule out the presence of disease causing mutation in other genes in MADD and other diseases caused by multiple genes.

Early detection of glutaric aciduria type I by newborn screening in Taiwan

BACKGROUND/PURPOSE

Glutaric aciduria type 1 (GA1) is an inborn error of lysine and tryptophan metabolism. There is a lack of initial diagnostic signs of the disease, but late treatment often results in severe neurologic impairment. In this study, we analyzed the results of screening for GA1 in a Chinese population.

METHODS

Dry blood spots were obtained at about 3 days of age from 357,307 newborns and tested for elevation of glutaryl (C5DC)-carnitine by tandem mass spectroscopy. A second sample of blood spots was required from those cases with abnormal elevation of C5DC-carnitine (higher than the cut-off value) (recall). If the results remained abnormal, those cases were referred for confirmation of the diagnosis and treatment.

RESULTS

Between August 2001 and February 2005, there were 40 cases with C5DC-carnitine more than 0.13 microM (the cut-off value), from whom a second sample of blood spots was obtained (recall rate, 0.02%); two cases were confirmed to be affected by GA1. Because of the low positive prediction rate using this cut-off value, we elevated the cut-off value slightly. Between February 2005 and August 2006, there were eight cases with C5DC-carnitine more than 0.22 microM from whom a second sample of blood spots was obtained (recall rate, 0.01%); three cases were confirmed to be affected by GA1. All five cases with persistent elevation of C5DC-carnitine were referred and diagnosis was confirmed in each, giving an incidence of 1 in 71,461 newborns. There were no false negatives. Magnetic resonance imaging studies obtained from four cases showed frontotemporal atrophy at the time of diagnosis. Two cases were followed for over 1 year, and under treatment with dietary control and carnitine supplementation, both had normal development and neither exhibited a frank episode of encephalopathic crisis.

CONCLUSION

With properly established cut-offs, GA1 can be successfully screened for in populations with a low incidence of the disease. Early treatment is likely to improve the outcome of cases discovered by screening.

A novel ABCD1 gene mutation in a Chinese-Taiwanese patient with adrenomyeloneuropathy

The ABCD1 gene mutation (previously ALD) has been reported in China, but not previously in Taiwan. This case report describes one Taiwanese patient whose clinical manifestations were compatible with adrenomyeloneuropathy. Direct sequencing for the ABCD1 gene of this patient and his mother detected a novel missense mutation, K513Q, in exon 6, the first such detected in a Taiwanese patient. Previous studies have suggested exon 6 as a possible hot segment of ABCD1 gene mutations in Chinese populations; however, most of the mutations in exon 6 presented as childhood cerebral adrenoleukodystrophy. K513Q is also the first novel mutation located within exon 6 and presenting with adult-onset adrenomyeloneuropathy in Chinese-Taiwanese.

A novel functional assay for simultaneous determination of total fatty acid beta-oxidation flux and acylcarnitine profiling in human skin fibroblasts using (2)H(31)-palmitate by isotope ratio mass spectrometry and electrospray tandem mass spectrometry

BACKGROUND

Two separate and complementary assays, total mitochondrial fatty acid beta-oxidation (FAO) flux rate and acylcarnitine profiling, have been used to establish a definitive diagnosis of FAO defects (FAOD) in cultured cells. We developed a novel functional assay for total FAO rate assay by measurement of deuterated water enrichment and to combine it with the conventional acylcarnitine profiling method into a single tracer incubation experiment.

METHODS

Skin fibroblasts were incubated in a medium containing universal deuterium-labeled palmitate ((2)H(31)-palmitate) and l-carnitine without glucose supplementation for 96 h. The culture medium was assayed for deuterated water enrichment using isotope ratio mass spectrometry (IRMS) and acylcarnitine profiling by electrospray-ionization tandem mass spectrometry (ESI/MS/MS).

RESULTS

The medians of (2)H(2)O enrichment after 96 h of incubation of (2)H(31)-palmitate of the control, other inherited metabolic diseases and FAOD cell lines were 109.9, 102 and 23.1 ppm/mg protein/96 h, respectively. All fibroblasts with FAOD except carnitine uptake defective, multiple acyl-CoA dehydrogenase and short-chain 3-hydroxyacyl-CoA dehydrogenase deficient cells were well separated from the control (<60% control median, p<0.05) and could be identified by IRMS assay. Accumulations of disease-specific acylcarnitines due to blockage in the carnitine cycle and FAO spiral were also demonstrated by acylcarnitine profiling.

CONCLUSIONS

This novel functional assay is less time consuming and relatively simple by comparison to other published methods and can be used to investigate patients suspected to have FAO defects.

A genomic approach to mutation analysis of holocarboxylase synthetase gene in three Chinese patients with late-onset holocarboxylase synthetase deficiency

OBJECTIVE

Multiple carboxylase deficiency (MCD, MIM:253270) is a common organic aciduria and caused by deficiency of either biotinidase or holocarboxylase synthetase (HLCS; EC 6.3.4.10). Patients commonly present during early infancy with acute metabolic derangements and severe metabolic acidosis. Recently, a late onset form of HLCS deficiency was also described. The different phenotypes (early and late presenting) may be related to a spectrum of mutations in HLCS gene. Applications of mutation analysis in HLCS had been limited previously by the requirement of cDNA from living tissue for study. We described here a genomic approach for molecular diagnosis of HLCS deficiency which we have used to detect mutations in Chinese patients who had the late-onset form of HLCS deficiency. In addition, a fibroblast cell line with MCD from Coriell Cell repositories was also studied.

DESIGN AND METHODS

Three Chinese patients with late onset HLCS deficiency were studied. The genomic sequence of HLCS was retrieved and newly designed primers were used to cover all coding sequences of the gene. PCR products were analyzed by direct sequencing. Population allelic frequencies of mutations detected were determined by genotyping of control samples by restriction fragment length polymorphism.

RESULTS

We found a recurrent mutation, R508W, in the three unrelated Chinese patients. Two were homozygous for this mutation. The other patient was a compound heterozygote of R508W and a novel mutation, D634N. The results suggest that R508W may be an important and relatively prevalent disease-causing mutation in Chinese MCD patients. A fibroblast cell-line from an African patient revealed an additional novel mutation, R565X and a known mutation, V550M.

CONCLUSION

R508W is a recurrent mutation in Chinese MCD patients which is associated with the late onset phenotype. This new genomic approach for mutation analysis of HLCS gene provides new opportunities in studies of MCD.