1 Inherited metabolic diseases in the Southern Chinese population Dis - PDF document

1 Inherited metabolic diseases in the Southern Chinese population; Diseases Spectrum and estimated incidence from recurrent mutations Joannie Hui1, 6*, Nelson LS Tang2,3, 6,7* , CK Li, LK Law, KF To, Phyllis Yau , Simon LM Fung, Josephine SC Chong, Lilian TsungGrace Chiang, Eva Fung, KL Cheung, WL Yeung, TF Fok 1 Department of Pediatrics, Prince of Wales Hospital, Hong Kong 2 Department of Chemical Pathology, 3 Li Ka Shing Institute of Health Sciences and 4 Department of Anatomical and Cellular Pathology Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong 5 Department of Dietetics, and 6Joint Metabolic Clinic, Prince of Wales Hospital, Hong Kong. 7 Shenzhen Research institute, Chinese University of Hong Kong, Shenzhen * These authors contributed equally Corresponding author: Nelson L.S. Tang, MD, FRCPA Department of Chemical Pathology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, China. Phone: +852 26322320; Fax: +852 26365090; E-mail: nelsontang@cuhk.edu.hk This manuscript consisted of 4,647words, 30 pages, 2 figures and 2 tables. 2 Summary (200-250 words) 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 characterized 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 Southern Chinese. Comparison with other populati

ons 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 hyperphenylalaninemia 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 summarized here which may be useful for clinical practice. In addition, data will also be useful for policy makers in planning of newborn screening program and resource allocation. 3 Keywords (� 3 keywords) Inherited metabolic disease; Inborn errors of metabolism; Biochemical genetics; Fatty acid oxidation defects; Newborn screening program; Enzyme replacement therapy. List of Abbreviations

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\n /0/.\n'' 4 1.Introduction 1.1Recent Progress in IMD Inherited metabolic diseases (IMDs) are a diverse group of disorders caused by inherited defects of various metabolic pathways. These defects in metabolic pathways lead to either accumulation of toxic side products or deficiency of essential metabolites. Some patients with severe defects may die suddenly during the first year of life or suffer from severe symptoms and syndrome. In the past, treatment options were few and prognosis was poor. However, in the recent 10 to 20 years, we witnessed a major advance and breakthrough in both screening (early diagnosis) and therapy for IMDs 1-6. Although individual metabolic disease is relatively rare, IMDs as a group represent a significant healthcare burden collectively. For example, collective incidences ranging from 1 in 2,500 to 1 in 4,000 have been reported in European countries and many of them could be detected early by screening at the newborn period 7, 8. The spectrum of IMDs is well characterized in Caucasians as several clinical cohorts have been reported from Canada, Italy, England and Spain7-10. Few studies had been carried out in other populations like Japan, Indian and Saudi Arabia11-13. While the Chinese population represents 18% of the world population, few cohort studies of IMDs had been reported. A Taiwan group reported incidences of IMDs identified by newborn screening14, 15, however, information was confined only to diseases that had been included in the screening program. 5 It is now apparent that the spectrum of diseases is different between the

Asian and European populations 16-18. Therefore, it is important to understand what are those prevalent diseases in the Chinese population. 1.2Development of a metabolic clinic in Hong Kong In January 1997, a Joint Metabolic Clinic in Hong Kong was set up at the Prince of Wales Hospital/CUHK to diagnose and provide treatments to patients with IMDs. By 2010, more than 100 patients and families had been diagnosed and treated in this metabolic clinic which covers an catchment area of a population of 1.2 million. A profile of the more common IMDs in the Chinese population in Hong Kong has also emerged from our case series database. Part of it has been described in an earlier review reported by our team 16. Several unique features are apparent in the spectrum of diseases found in the Southern Chinese. For example, primary carnitine deficiency is more common in Chinese due to presence of a founder mutation 19, 20. And classical phenylketonuria (due to defective phenylalanine hydroxylase, PAH) was relatively rare comparedto another defect in causing hyperphenylalaninemia (6-pyruvoyl-tetrahydropterin synthase deficiency) 16. The data of this case series gathered after more than 10 years’ of experiences in running the metabolic clinic will be useful for policy makers in planning of newborn screening program 21, 22 and resource allocation involved in both screening and long-term treatment as many IMDs have major resource implications nowadays both due to the chronic nature of the disease or disability and emerging therapy regimens which are often costly 21, 23-25. 6 2.Overview of disease spectrum and comparison wi

th other populations (Figure 1) In order to allow comparison with data from Western countries, IMDs were grouped according to the conventional classification into two major categories: (A) Diseases of Small Molecules and (B) Diseases of Large Molecules. Under the category of Diseases of Small Molecules, examples include organic acidurias, defects in fatty acid oxidation pathway, inherited defects involved in metabolism of amino acids, primary lactic acidosis and defects in the urea cycles. On the other hand, various storage diseases with tissue deposition of large polymeric molecules, like in mucopolysaccharidoses, glycogen storage diseases and other organelle diseases are grouped into Diseases of Large Molecules. Figure 1A shows the proportional distribution of the 2 categories which turns out to be largely even. In order to make comparison with incidence data from the Western countries, diseases are further subdivided according to Applegarth et al . It is interesting to note that the case-mix would become fairly similar if two highly prevalent IMDs in Caucasians were excluded, namely classical PKU and galactosemia . 7 3.Diseases of small molecules 3.1. Organic acidurias (Figure 2) The prevalences of three common organic acidurias stand out from the rest as multiple unrelated patients were diagnosed in our clinic. They are (1) glutaric aciduria type 1, (2) multiple carboxylase deficiency and (3) propionic aciduria. A particularly high prevalence of glutaric aciduria type 1 and multiple carboxylase deficiency was found in Southern Chinese when compared to Northern Chinese in Shanghai or Beijing 17, 26 or

Caucasian populations 7, 9 (Figure 2). All the three locally prevalent organic acidurias can be treated with dietary and pharmacological interventions and could lead to good prognosis27. 3.1.1.Glutaric aciduria type 1 (GA1) Early prophylactic treatment of patient with Glutaric aciduria type 1 before acute neurological crisis is the key advance in treatment of this disease 28. In Western countries and in Taiwan where universal newborn screening (NBS) is carried out, it is straight forward to start prophylactic treatment once the NBS result is confirmed 29, 30. On the other hand, it is difficult to identify pre-symptomatic patients of GA1 in regions without universal NBS. The importance of pre-symptomatic treatment cannot be overemphasized as neurological sequel cannot be reversed after acute neurological crisis. In the clinic, one case was picked up by clinical suspicions due to the associated phenotype of big head (head circumference �95 percentile). The patient has been treated with dietary intervention and has been well on the latest follow-up at 9 years old. 8 Our early study found that IVS10-2A�C mutation was a recurrent mutation 31. Screening of the IVS10-2A�C mutation showed that population carrier rate was as high as 1/120 (95% Confidence Interval, CI = 0.0002 to 0.0456) suggesting a disease incidence of ~ 1 / 60,000. Subsequent regional newborn screening in China confirmed a similar disease incidence at 1/64,70832. This mutation was also found in Taiwan Chinese patients 33-35. 3.1.2.Multiple carboxylase deficiency (MCD) Multiple carboxylase deficiency could be due to defect in

either one of the 2 genes: holocarboxylase synthetase (HLCS) deficiency and biotinidase deficiency. This disease is characterized by life-threatening metabolic decompensation during infancy. Treatment response is excellent if the patient could overcome the acute crisis. Again, NBS will be an excellent cost-effectiveness way to diagnose this disorder. In Caucasian population, biotinidase deficiency screening had been implemented on filter paper blood spot sample for decades even before the era of NBS by tandem mass spectrometry 36. In this case series, only one case of biotinidase deficiency was diagnosed while HLCSdeficiency was the cause in another 4 MCD patients. In terms of phenotype, we did not find any key difference between biotinidase and HLCS deficiency, and therefore, a definitive diagnosis by enzyme assay or mutation analysis will be required. Our collection of MCD cases is highly responsive to treatment with biotin. And prognosis is excellent. 3.1.3.Other organic acidurias 9 Propionic acidemia and methylmalonic acidurias are the most common types of organic aciduria in the global populations (Figure 2). However, the prevalence of both diseases are low in our population. In summary, two unique features are described for the spectrum of organic acidurias. First, the predominant etiology of MCD in Southern Chinese is HLCSdeficiency, while biotinidase deficiency was more common in Northern China (Shanghai and Beijing) and Caucasian populations. Second, the prevalence of methylmalonic aciduria was low in Southern China when compared to the rest of the World. These early impression requires further confi

rmation after NBS implementation in the future. 3.2.Fatty acid oxidation defects (FAOD) 3.2.1.Primary carnitine deficiency Our group has a long-term research interest in FAOD in Chinese. We are among the first to identify the causative gene (SLC22A5, also known as OCTN2) in primary carnitine deficiency due to defect of the plasma membrane carnitine transporter 19, 37, 38. Patients with this transporter defect have very low intra-cellular level of carnitine. As the same transporter is used for active re-absorption of free carnitine in the proximal renal tubule, the defect also leads to a severe renal wasting of carnitine and in turn the free carnitine in circulation is also low. Therefore, a very low free carnitine and total carnitine 10 are the hallmarks for diagnosis of this potentially life-threatening disease 39. Patients responses extremely well to high dose carnitine replacement and the very first three cases diagnosed in America showed favorable prognosis 40. This defect is highly relevant to Southern Chinese population due to the presence of a common mutation, R254X 20. The population carrier frequency of R254X was 1/125 (95% CI=0.0002 to 0.0438) in Southern China 20. This disease was also the most prevalent disease among all FAOD in a Taiwan newborn screening program41. 3.2.2Carnitine-acylcarnitine translocase deficiency Carnitine-acylcarnitine translocase (CACT) deficiency is characterized by early onset of severe metabolic decompensation and poor prognosis. Many studies suggested poor treatment outcome and prognosis 42, 43. It is also a common cause of unexplained death in early infancy period

or sudden infant death. Few patients with good treatment response were reported recently 44, however long term follow-up is required to confirm these initial favorable response. Stanley et al reported the first patient of this disease who was born to an American Chinese family in 199245. Interestingly, this patient shared a recurrent splicing mutation (IVS2-10T�G) with another Chinese patient from a British-Chinese family 46. Later, this mutation was also found in other local Chinese cases of sudden death43,47. Therefore, this recurrent mutation may be present at a high frequency in the Southern Chinese population. All 3 patients in this case series presented with severe metabolic crisis in early infancy and succumbed to the disease. Early onset of cardiac arrhythmia was frequently found. Therefore, it might serve as a clinical marker to raise the suspicion of pediatrician 11 about this differential diagnosis in patients with early onset metabolic crisis. Although prognosis may not be favorable in the index case, it is very important to make the diagnosis as it will enable pre-natal diagnosis in subsequent pregnancy. 3.2.3Multiple acyl-CoA dehydrogenase deficiency / glutaric aciduria type 2 Another common FAOD in Chinese is multiple acyl-CoA dehydrogenase deficiency. The defect may be caused by mutation in one of its subunits encoded by three genes (electron transfer flavoprotein alpha-subunit, ETFA; electron transfer flavoprotein beta-subunit, ETFB, and ETF dehydrogenase, ETFDH). The spectrum of mutations and their distribution among these 3 genes in our local patients had been reported 48. Remarka

bly, one of the mutation in ETFDH (A84T) was found to be a common mutation in subsequent studies 49, 50 . 3.2.4Very long-chain acyl-coenzyme A dehydrogenase (VLCAD) deficiency VLCAD deficiency may present with both neonatal (early-onset) and adult form. We diagnosed adult patients referred from another catchment area who presented with severe myopathy. Therefore, they did not appear in the statistics reported here (Table 1). However, this is an important diagnosis to recognized as it may present with highly variable phenotypes ranging from sudden death in its neonatal form to cardiomyopathy or even isolated myopathy in adult patients 51. Blood carnitine profiling is the key investigation for making the diagnosis. 3.2.5Medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency 12 MCAD deficiency is very common in Caucasian with an incidence of 1 in 17,000, however, it is extremely rare in Asian. The high incidence in Caucasian is due to the presence of a common mutation (c.985A�G). Although this mutation was first found by Japanese research team, it was not present in many Asian populations 14, 52. Only two patients were diagnosed in the Taiwan NBS program over 9 years which suggested an incidence of 1 in 660,000 for Southern Chinese 14. 3.2.6Short-chain acyl-coenzyme A dehydrogenase (SCAD) deficiency and other variants of uncertain phenotype SCAD deficiency is a defect in the final step of the fatty acid oxidation spiral and SCAD handles acyl-CoA of 4 to 6 carbons in length. It is not unexpected that SCAD patients may have milder phenotype and present at variable age (from newborn to 50 years old) 5

3. Both phenotype and severity of disease are highly variable. Some patients present with metabolic acidosis. On the other hand, asymptomatic cases were also reported in families with clinically affected sibs. Histologic features of myopathy and lipid storage disease had been found in some patients 54. A common polymorphism in ACADS gene, c.625G�A, was found across ethnic groups. Previous reports suggested that individual homozygote for this polymorphism had a wide spectrum of clinical manifestations ranging from asymptomatic carrier to myopathy 55. A polymorphism in the CPT2 gene was also common in Asian population (c.1055T�G or F352C) 56. This polymorphism encodes for a carnitine palmitoyltransferase 2 protein that is believed to be thermolabile. Therefore, it might lead to a phenotype of transient CPT2 13 deficiency and raised serum acylcarnitine ratio only during febrile illness. Subsequent study in Japan showed that this polymorphism might be associated with higher mortality in patients with acute encephalopathy57. 3.3Aminoacidopathies 3.3.1Citrullinemia type 2 or citrin deficiency The most common aminoacidopathy found in our series is citrin deficiency, also known as neonatal onset type 2 citrullinemia (#MIM:605814) or neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD). This defect in the aspartate/glutamate carriers functioning as aspartate-malate NADH shuttle across the mitochondrial membrane was first reported in adult patients with neuro-psychiatric symptoms and hyperammonemia called adult-onset type II citrullinemia (CTLN2, #MIM:603471) 58. Only until 2001, the neo

natal form was firstly recognized in patients presented with conjugated hyperbilirubinemia during neonatal or early infancy 59 We diagnosed 7 patients and citrin deficiency represented the most common IMD in this series. Galactouria was a frequent finding among our patients. This is a particularly important diagnostic marker relevant to Asian population, as the incidence of classic galactosemia is very low in Southern Chinese 60, it can serve as a surrogate marker for citrin deficiency. Recently, a second-tier molecular test approach has been proposed for this disorder61. 3.3.2Hyperphenylalaninemia (HPA) 14 A strong geographic differentiation was found in disorders leading to HPA. As already mentioned in the earlier review, classic phenylketonuria due to mutations in PAHgene, (PKU, #MIM:261600) was less common in Southern Chinese when compared to Caucasian. On the other hand, a higher proportion of HPA was caused by deficiency of 6-pyruvoyl-tetrahydropterin synthase (PTS, #MIM:261640) leading to tetrahydrobiopterin-deficient HPA. Hsiao KJ’s team studied mutations and causes of tetrahydrobiopterin-deficient HPA in Taiwan and found common recurrent mutations in PTS genes which explained the high regional prevalence 62 They showed that PTS deficiency was more prevalent among the Southern Chinese while classic PKU was more common among Northern Chinese63. Two patients with PTS deficiency were also diagnosed and treated in this case series. Both of them also carried the common mutations. Similarly, two patients with classic PKU were also seen in the clinic. 3.3.3Other aminoacidopathies A variety of other ami

noacidopathies were also seen but they were diagnosed in single families. And no definitive statement about their prevalence could be made. These disorders included cystinuria and pyridoxine-responsive homocystinuria due to CBS mutations 64. 3.4Urea cycle defects Ornithine transcarbamylase (OTC) deficiency represents the most common urea cycle defect in our clinic and it is also the case in other Asian populations65. In addition to the typical presentation of OTC deficiency, we also found variant phenotypes; including symptomatic female carrier 16 and mild phenotype in a male patient with intermittent 15 hyperammonemia 66. These patients illustrate the complexity and the range of phenotypic variation in this X-linked disorder. Disease of Large Molecules (including Storage and Organelle Diseases) and others 4.1Glycogen Storage Diseases (GSD) Almost all types of hepatic glycogen storage diseases had been diagnosed in Hong Kong. All patients are characterized by a huge hepatomegaly. Among the various types, Glycogen storage disease type 1 is important to recognize as patients may suffer from life-threatening hypoglycemia. All type 1 patients experienced hyperlipidemia, lactic acidosis and high blood uric acid concentration. The main difference between type 1 and other types of hepatic GSD is that the other types (particularly type VI and IX) are presented with milder phenotype 67, 68. These (non-type 1) patients have a huge hepatomegaly to the same extent as type I GSD patients, but they might presented late (even undiagnosed after infancy) and without hypoglycemia. Pompe disease (GSDII) represented a special

type of glycogen storage disease to recognize and enzyme replacement therapy is useful particularly in late-onset patients69, 70. 4.2Lysosomal Storage Diseases (LSD) Lysosomal storage diseases (LSDs) are a group of approximately 50 known genetic disorders which are due to deficiency of a particular enzyme or enzymes causing abnormal storage of naturally occurring molecules inside lysosomes 4, 5, 71, 72.Up until 16 2010, there were 31 patients with various types of LSDs that have attended our clinic. These included 21 patients with Mucopolysaccharidoses (6 MPS I, 5 MPS II, 5 MPS III, 1 MPS IV & 4 MPS VI), 5 patients with Mucolipidosis II (I-cell disease), 1 patient with Niemann Pick type B, 3 patients with Niemann-Pick type C disease (NP-C) and 1 patient with infantile Pompe disease. It is worth pointing out that Gaucher disease was not included in our case series though patients were found Hong Kong and in other parts of China 73, 74. 4.3Primary lactic acidosis A variety of mitochondrial diseases have been diagnosed. Both mitochondrial respiratory chain defects (RCD) and pyruvate dehydrogenase (PDH) deficiency can lead to primary lactic acidosis. For the patients with confirmed diagnosis of PDH deficiency with enzyme assay on cultured fibroblast, they had distinctive features compared to other patients with respiratory oxidation chain defects. These features include early-onset of lactic acidosis (particularly in male PDH deficiency patients as it is a X-linked disease), persistently very high level of blood lactic acid concentration (� 6 mmol/L) and presence of specific CNS structural abnormalit

y which could be picked up on CT scan or MRI (such as corpus callosum agenesis). 4.4Others IMDs 4.4.1Peroxisomal diseases X-linked adrenoleukodystrophy (XALD) was the most common peroxisomal diseases. It is an X-linked disease due to mutation in the ABCD1 gene encoding for a 17 protein required for importing very-long chain acylCoA dehydrogenase into the peroxisomes. Therefore, patients have abnormally high level of very-long chain fatty acid in the circulation which is also a reliable diagnostic marker. It is important to diagnose this condition early as pre-symptomatic patients carrying mutations need to be monitored closely for onset of white matter changes, signifying imminent leukodystrophy. Definitive treatment such as bone marrow transplantation is required as early as possible when such changes are evident 75. As majority of our XALD patients already had severe neurological involvement at the time of presentation, they were not suitable candidates for hematopoietic stem cell transplant. Five patients underwent transplant and three of them showed no further deterioration in their neurological status at 5-year follow up. One patient died shortly after transplant because of relentless disease progression. 4.4.2Neurogenetic disorders Various defects involving synthesis and metabolism of neurotransmitters were also found. They included tyrosine hydroxylase deficiency and GTP cyclohydrolase 1 deficiency, some of them had been reported in previous case series analysis 76 Two patients with glucose transporter defect had been reported 77. In addition, it was also important to recognize that patients with

hyperphenylalaninemia caused by PTSmutations also suffered from deficiency of neurotransmitters dopamine and serotonin 78and they would be benefited by treatment with L-dopa/carbidopa/5-hydroxytryptophan plus BH4 with marked clinical improvement. 18 Discussion 5.1Difference in spectrum of IMDs between Northern and Southern Chinese Hong Kong is located at the southern coastal part of China and is densely populated with more than 7 million residents. About 95% of the population is Han Chinese79. A large proportion of them are descendants of the past episodic influxes of people from neighboring South China provinces, in particular, Guangdong. Therefore, the population genetic make-up is mainly that of Southern Chinese. It is now generally accepted that genetic difference exists between the Northern and Southern Chinese. It has been hypothesized that Northern Chinese are descendants of settlements from taken North migration route, while the Southern Chinese are the offsprings of another migration event using routes through Southeast Asia 80, 81. There are now ample evidences supporting genetic differentiation between Southern and Northern Chinese based on different genetic markers, such as SNPs and mitochondrialhaplotypes 81, 82. Geographically, an arbitrary dividing line has been placed in the Qinling Mountains and Huai River, but recent evidence supports for Yangtze River being a division. Such genetic differentiation is also reflected in different spectrum of common IMDs in Southern Chinese as compared with that in Northern Chinese as well as in Caucasian. For example, classic PKU is less common in S

outhern Chinese. In contrast, the incidences of PKU are comparable between Northern Chinese and Caucasians 17. Likewise, methylmalonic and isovaleric acidaemia are among the most frequent organic acidurias found in Northern Chinese but not so frequent in Southern Chinese 17, 19 26. Our data on Southern Chinese will provide more in-depth comparison when more data from centers in Northern China become available. 5.2Estimation of the incidence of common IMDs in Southern Chinese An important reason to estimate the incidence of IMDs is for planning and implementation of NBS and treatment service. At the moment, the main application of NBS is targeted to small molecule diseases. Therefore, estimates of incidence of these IMDs are particularly of interest. However, reliable disease incidence cannot be determined from the crude incidence rate from case series data like this study. Without a territory-wide registry or NBS, it is not possible to have an unbiased denominator to figure out disease incidence. As a result, a tendency of overestimation is common in case series data. For example, if we assume these patients were collected over the course of 13 years in this catchment area, the resulting incidence rate will be several folds higher than figures reported in other populations 83. Many reasons lead to overestimation in case series, including cross-catchment area referral, inclusion of prevalent cases which had not been diagnosed (backlog effect) and immigration of children particularly those born to non-local residence. As an alternative we used observed population carrier (heterozygote, 2pq) frequencies of co

mmon mutations to calculate the homozygote frequencies (q) as estimates of disease incidence. Table 2 summarizes IMDs with recognized common recurrent or founder mutation in Southern Chinese. Seven of them could be picked up by NBS using tandem mass spectrometry. Incidences of these 7 IMDs range from 1 in 20 17,000 to 1 in 60,000. They are consistent with incidence determined from a newborn screening program in Taiwan 41. All together, ~1 in 5,400 live births would have one of these locally “common” IMDs. We estimate that ~15 newborns with IMDs might be benefited from a universal NBS every year given the current annual birth rate at ~ 80,000 in Hong Kong. This figure is also comparable to that in the USA in which a high coverage NBS has been in place. As MCAD deficiency and galactosemia are not prevalent in Southern Chinese, we compared to the incidence of small molecular diseases in US population after removal of both entities, which would become ~1 in 7,000 83. Recently, not only small molecule diseases are screened by NBS, storage diseases like Pompe disease and LSD are also potential diseases for screening. Expanding the NBS to cover large molecular diseases will allow early diagnosis and treatment of these patients 84. 21 Acknowledgement We are grateful to funding bodies which have supported our work and provision of service to IMDs patients, including S.K. Yee Medical Foundation and the Sir Robert Ho Tung Charitable Fund. Part of the data has been presented in abstract form in 9th Asia Pacific Conference on Human Genetics and 1st Asian Congress for Inherited Metabolic Diseases in Fukuoka 2010. We thank a

ll health care workers contributed to service of the metabolic clinic. We are also extremely grateful to patients and their families. We also thank Wang Xiansong for help with manuscript preparation. 22 Figure Legends Figure 1. Prevalence of two categories of Inherited Metabolic Diseases in Hong Kong Chinese. (1A) The proportion of two major categories of IMDs. (1B) Diseases subgroups . Figure 2. Comparison of prevalence of various organic acidurias among Southern Chinese, Northern Chinese and Caucasian populations. Data are extracted from references 7, 9, 17, 26. 23 Table 1. Diagnoses and spectrum of IMDs of patients seen in a metabolic clinic in Hong Kong. Diseases of Small Molecules Organic Aciduria Glutaric aciduria I 4 Propionic acidemia 2 Holocarboxylase synthetase deficiency 4 Biotinidase deficiency 1 HMG-CoA lyase deficiency 1 Fatty acid oxidation defects Carnitine acylcarnitine translocase deficiency 3 Glutaric aciduria type 2 (Multiple acylCoA dehydrogenase deficiency) 4 Short chain acylCoA dehydrogenase deficiency 1 Primary carnitine deficiency 1 Aminoacidopathies Citrin deficiency 7 Tetrahydrobiopterin-deficient HPA(PTS deficiency) Classic PKU Cystinuria 2 Homocystinuria 1 Urea cycle defects Ornithine transcarbamylase deficiency 2 Others Galactosemia 1 Xanthine oxidase deficiency 1 Diseases of Large Molecules Glycogen Storage Diseases Glycogen storage disease Ia 2 Glycogen storage disease Ib 2 Glycogen storage disease III 2 Glycogen storage disease VI 1 Glycogen storage dis

ease IX 2 Pompe disease 1 Lysosomal Storage Diseases Mucopolysaccharidosis I 6 Mucopolysaccharidosis II 5 Mucopolysaccharidosis III 5 Mucopolysaccharidosis IV 1 Mucopolysaccharidosis VI 4 I cell disease 5 24 Niemann Pick Type B 1 Niemann Pick Type C 3 Organelle Diseases Primary lactic acidosis Pyruvate dehydrogenase deficiency 2 Complex I deficiency 2 Complex IV deficiency 1 Leigh’s disease 3 Kearns Sayre syndrome 2 Peroxisomal diseases Adrenoleukodystrophy 15 Peroxisomal biogenesis disorder 1 Neurogenetic Disorders Tyrosine hydroxylase deficiency 4 GTP cyclohydrolase 1 deficiency 1 Glucose transporter defect 2 Vanishing white matter disease 1 25 Table 2. Recurrent or founder mutations found in IMDs among Southern Chinese Disease / Gene Mutation Carrier frequency* Estimated incidence Expected cases per 100,000 newborns Reference Organic acidurias Glutaric aciduria type 1/ GCDH IVS10-2A�C 1 / 120 Hong Kong 1 in 60,000 1.67 31 Multiple carboxylase deficiency/ HLCS R508W known recurrent mutation@ 1 in 60,000 1.67 85 Fatty acid oxidation defects Primary Carnitine deficiency / SLC22A5 (OCTN2) R254X 1 / 125 Hong Kong 1 in 60,000 1.67 20 Carnitine-acylcarnitine translocase / SLC25A20 IVS2-10T�G known recurrent mutation@ 1 in 60,000 1.67 46 , 47 Glutaric aciduria type 2/ ETFDH A84T (c.250G�A) 7 / 520 ^ Shanghai 1 in 22,500 4.44 48 , 86 , 87 Aminoacidopathies Citrin deficiency/ SLC25A13 851-854del IVS6+5G&#

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