Yuet-Ping Yuen

Fatal viral infection-associated encephalopathy in two Chinese boys : a genetically determined risk factor of thermolabile carnitine palmitoyltransferase II variants

Influenza-associated encephalopathy (IAE) is a potentially fatal neurological complication of influenza infection usually in the presence of high and persistent fever. Thermolabile carnitine palmitoyltransferase II enzyme (CPT-II) predisposes IAE, so far only described in Japanese. As the genetic origins of Japanese and Chinese are alike, similar genetic risk factors in CPT-II are expected. We report the first two unrelated Chinese patients of thermolabile CPT-II variants that underlain the persistent high fever-triggered viral infection-associated encephalopathy, multi-organ failure and death. Elevated (C16:0+C18:1)/C2 acylcarnitines ratio and the CPT2 susceptibility variant allele [p.Phe352Cys; p.Val368Ile] were detected. The asymptomatic family members of one patient also had abnormal long-chain acylcarnitines. In our experience of biochemical genetics, the elevated (C16:0+C18:1)/C2 acylcarnitines ratio is unusual and specific for thermolabile CPT-II variants. Allele frequency of [p.Phe352Cys; p.Val368Ile] among Hong Kong Chinese was 0.104, similar to Japanese data, and [p.Phe352Cys] has not been reported in Caucasians. This may explain the Asian-specific phenomenon of thermolabile CPT-II-associated IAE. We successfully demonstrated the thermolabile CPT-II variants in patients with viral infection-associated encephalopathy in another Asian population outside Japanese. The condition is likely under-recognized. With our first cases, it is envisaged that more cases will be diagnosed in subsequent years. The exact pathogenic mechanism of how other factors interplay with thermolabile CPT-II variants and high fever leading to IAE, is yet to be elucidated. Fasting and decreased intake during illness may aggravate the disease. Further studies including high risk and neonatal screening are warranted to investigate its expressivity, penetrance and temperature-dependent behaviors in thermolabile CPT-II carriers. This may lead to discovery of the therapeutic golden window by aggressive antipyretics and L-carnitine administration in avoiding the high mortality and morbidity of IAE.

Non-invasive urinary screening for aromatic L-amino acid decarboxylase deficiency in high-prevalence areas: a pilot study.

BACKGROUND The diagnosis of aromatic L-amino acid decarboxylase (AADC) deficiency, one of the pediatric neurotransmitter disorders, is classically made with plasma enzyme level or cerebrospinal fluid (CSF) neurotransmitter profile, while both are technically demanding and the latter requires the invasive lumbar puncture. So far less than 100 cases have been reported worldwide with 20% from Taiwan. It was postulated that the condition might have been under-diagnosed among Chinese populations and a non-invasive screening tool should be developed in areas with high prevalence. METHODS Urine metabolic profiles performed by gas chromatography-mass spectrometry (GC-MS) in a 31-month period were retrospectively reviewed: those with vanilmandelic acid concentration lower than one percentile plus the presence of 3-o-methyldopa were defined as positive and the patients were further evaluated. RESULTS Among 1046 metabolic profiles (from 845 patients) reviewed, 3 profiles from 2 patients were screened positive: both cases had compatible CSF neurotransmitter profiles and the diagnosis was further confirmed by genetic analysis of DDC gene. 13 negative urinary metabolic profiles from 7 patients who had CSF neurotransmitters analyzed were identified as controls: all 7 CSF neurotransmitter profiles were not compatible for AADC deficiency. CONCLUSIONS The GC-MS-based urine metabolic profiling was shown to be a satisfactory screening tool for AADC deficiency. Further confirmation can be performed by mutation analysis in the DDC gene, thus avoiding risks of lumbar puncture. We advocate all ethnic Chinese patients presenting with dystonia have their urine organic acids analyzed before proceeding to CSF neurotransmitters analysis.

NUDT15 variant and thiopurine-induced leukopenia in Hong Kong.

Thiopurines, including azathioprine and 6-mercaptopurine (6-MP), are widely used in the treatment of autoimmune diseases and cancers, as well as prevention of rejection in organ transplantation. Azathioprine is a pro-drug that is converted to 6-MP, and subsequently undergoes extensive metabolism to the formation of 6-thioguanine nucleotides (6-TGNs). Such 6-TGNs exert their therapeutic effect by inducing apoptosis of T lymphocytes.1 Myelosuppression, manifesting as a reduction in one or more of the haematopoietic lineages (most commonly leukopenia), is a serious adverse drug reaction related to the excessive generation of 6TGNs.2 Thiopurine S-methyltransferase (TPMT) diverts 6-MP from the formation of 6-TGNs by converting 6-MP into inactive metabolites. Thus, TPMT deficiency plays a causal role in the pathogenesis of thiopurine-induced leukopenia by shunting thiopurine metabolites towards the formation of excessive 6-TGNs. Genetic variants present in the TPMT gene result in TPMT deficiency and the trait is inherited in an autosomal co-dominant manner. TPMT*1 represents the wild-type allele with normal TPMT activity while *2, *3A, *3B, *3C, and *8 account for approximately 95% of all TPMT variants known to result in TPMT deficiency.3 With the conventional dose of thiopurines, individuals who have inherited two copies of the inactive TPMT allele (homozygous deficient) experience severe myelosuppression. A significant proportion (30%60%) of individuals who have inherited one copy of the inactive TPMT allele (heterozygous deficient) develop moderate-to-severe myelosuppression. Those who carry two wild-type TPMT alleles have the least myelosuppression. Prospective TPMT genotyping has been recommended by the US Food and Drug Administration.4,5 In addition, guidelines on TPMT genotype–based dosage recommendations are currently available that include a reduced thiopurine starting dose or use of an alternative non-thiopurine treatment in individuals who carry defective TPMT allele(s).6,7 In Hong Kong, many patients are prescribed Hong Kong Med J 2016;22:185–7 DOI: 10.12809/hkmj154783

The first case report of McLeod syndrome in a Chinese patient.

We report the first case of McLeod syndrome (MLS) in a 47-year-old Chinese man who presented with progressive limb weakness, chorea of feet, red blood cell acanthocytosis, absence of Kx red blood cell antigen and weak expression of Kell antigens. The diagnosis of MLS was confirmed by genetic testing showing a hemizygous mutation of XK gene. We review literature on neuroacanthocytosis in the Chinese population.

Role of postmortem genetic testing demonstrated in a case of glutaric aciduria type II.

Glutaric aciduria type II, or multiple acyl-CoA dehydrogenase deficiency, is a rare metabolic disorder inherited in an autosomal recessive manner. The condition can be caused by mutations in at least 3 genes, including ETFA, ETFB, and ETFDH. When this potentially lethal disorder is known for its clinical and biochemical heterogeneity, mutation analysis will be an invaluable part of diagnosis. We here described a Chinese adolescent boy who enjoyed good health earlier and presented at the age of 14 years with severe vomiting. His condition deteriorated rapidly and he succumbed shortly after. With a travel history before presentation and the late age of onset, diagnosis was particularly difficult. Findings in perimortem biochemical investigations and postmortem autopsy were guiding but not diagnostic. The diagnosis of glutaric aciduria type II was finally confirmed by mutation analysis performed by direct sequencing on genomic DNA from peripheral blood, which identified 2 different unreported missense mutations, c.502G>T (p.V168F) and c.786A>G (p.Q262R), in ETFA. The father and the mother were found to be heterozygous for the 2 mutations in ETFA respectively. Subsequent molecular family screening also ruled out the disease in his elder sister, who had a history of convulsion and a suspicious plasma acylcarnitine profile, and freed her from life-long supplementation. The case showed that molecular autopsies should be part of routine postmortem examination of unexplained sudden death in all age groups and DNA-friendly samples should be routinely collected and archived. In the era of personalized medicine with the power of modern genetics, molecular diagnosis should be obtained for heterogeneous diseases with different genetic defects but sharing similar clinical and/or biochemical phenotypes.

A novel ALDH5A1 mutation in a patient with succinic semialdehyde dehydrogenase deficiency

This is applicable to patients on once daily biotin supplementation but it may pose difficulties for those patients on multiple dose regimen. It has also been suggested that patient samples could be applied to a streptavidin agarose column to remove any biotin present before the immunoassay. We recommend that pathologists and scientists working in chemical pathology laboratories and clinicians should be aware of the potential assay interference of biotin on multiple immunoassay platforms entailing use of biotin-streptavidin interaction in their assay configurations. Alternative immunoassay methods not involving biotin-streptavidin interaction should be readily accessible for analysing samples from patients on biotin treatment. We believe that this is the most reliable and easiest way to avoid biotin interference. It would also be helpful if the laboratory information system is capable of generating an alert whenever blood specimens from a patient on biotin treatment are received. Effective mutual communications between clinicians and the laboratory need to be maintained with an aim to minimise the occurrence and impact of assay interference on clinical decision making and management.

Isolated persistent elevation of alanine transaminase for early diagnosis of pre-symptomatic Wilson’s disease in Chinese children

BackgroundRecent studies presented a contradictory approach for the investigation of pediatric patients with an isolated increase in alanine transaminase. While classical teaching advised for a thorough investigation, recent studies suggested the yield on further investigation was low and thus not necessary. Yet the approach to the same clinical problem may need to be different due to variable disease prevalence rates among different ethnic populations. For the population with a higher prevalence rate of genetic liver diseases like Wilson’s disease, an abnormal liver function may be the first presenting feature for some patients.MethodsWe reviewed 10 Chinese children with Wilson’s disease who were diagnosed at a presymptomatic stage because of an isolated persistent elevation of alanine transaminase.ResultsAll 10 patients did not have overt symptoms of liver impairment or neurological deficit. They were picked up incidentally with an abnormal liver function test. All patients were started on treatment shortly after diagnosis, and they remained well and symptom-free on the latest follow-up.ConclusionsThis case series illustrated that an isolated persistent elevation of alanine transaminase is an important clue to the early diagnosis of pre-symptomatic Wilson’s disease. It is particularly relevant in the Asian population where the disease is more prevalent.

NMR-based urinalysis for rapid diagnosis of β-ureidopropionase deficiency in a patient with Dravet syndrome.

BACKGROUND Beta-ureidopropionase deficiency is a rare inborn error of metabolism (IEM) affecting pyrimidine metabolism. To-date, about 30 genetically confirmed cases had been reported. The clinical phenotypes of this condition are variable; some patients were asymptomatic while some may present with developmental delay or autistic features. In severe cases, patients may present with profound neurological deficit including hypotonia, seizures and mental retardation. Using NMR-based urinalysis, this condition can be rapidly diagnosed within 15 min. CASE An 11-month-old Chinese boy had dual molecular diagnoses, β-ureidopropionase deficiency and Dravet syndrome. He presented with intractable and recurrent convulsions, global developmental delay and microcephaly. Urine organic acid analysis using GC-MS and NMR-based urinalysis showed excessive amount of β-ureidopropionic acid and β-ureidoisobutyric acid, the two disease-specific markers for β-ureidopropionase deficiency. Genetic analysis confirmed homozygous known disease-causing mutation UPB1 NM_016327.2: c.977G>A; NP_057411.1:p.R326Q. In addition, genetic analysis for Dravet syndrome showed the presence of heterozygous disease-causing mutation SCN1A NM_001165963.1:c.4494delC; NP_001159435.1:p.F1499Lfs*2. CONCLUSIONS The differentiation between Dravet syndrome and β-ureidopropionase deficiency is clinically challenging since both conditions share overlapping clinical features. The detection of urine β-ureidoisobutyric and β-ureidopropionic acids using NMR or GC-MS is helpful in laboratory diagnosis of β-ureidopropionase deficiency. The disease-causing mutation, c.977G>A of β-ureidopropionase deficiency, is highly prevalent in Chinese population (allele frequency=1.7%); β-ureidopropionase deficiency screening test should be performed for any patients with unexplained neurological deficit, developmental delay or autism.

The Online Diagnosis System for sanger sequencing based genetic testing

Sanger sequencing based genetic testing has been well established for many genetic diseases. In these testings, DNA sequencers produce vast amounts of data that need to be interpreted by the clinicians within a short peiod of time. To achieve this goal, a bioinformatics platform that can automates this process is yet to be developed. To fulfill this gap, we developed Online Diagnosis System (ODS), which is implemented as a web server and supports the commonly used ABI trace file format generated from Sanger sequencing. ODS seamlessly integrates useful functions covering base calling, Small Nucleotide Variant (SNV) identification, and comprehensive SNV annotation. It also allows the clinicians to manually inspect the quality of the identified SNVs when generating the final report. ODS can therefore significantly reduce the data analysis time, allowing the completion of the genetic testing in a timely manner.

The first report of a Chinese family with McLeod syndrome

We report the first case of a Chinese family with McLeod syndrome (MLS). The two affected brothers show significant phenotypic heterogeneity. The index case has peripheral acanthocytosis, choreoathetosis of his feet, a slowly progressive neuropathy and myopathy, and an elevated serum creatine kinase (CK) level. His elder brother has more prominent chorea of the shoulders, epilepsy, a rapidly progressive neuropathy and normal serum CK. The diagnosis of MLS was confirmed by a genetic test which showed a hemizygous frameshift mutation in the XK gene.