Diagnosis of Niemann-Pick disease type C with 7-ketocholesterol screening followed by NPC1/NPC2 gene mutation confirmation in Chinese patients

Background

It has been reported that oxidation product of cholesterol, 7-ketocholesterol, increases in plasma of patients with NP-C. Previously, we established a rapid test to determine the plasma 7-ketocholesterol level and found it elevated significantly in patients with acid sphingomyelinase deficient NPD and NP-C disease.

Methods

Individuals randomly referred to our outpatient clinics in the past two years for hepatosplenomegaly or isolated splenomegaly, who have been excluded as acid sphingomyelinase deficient NPD or Gaucher disease, and individuals with newborn cholestasis, psychomotor regression/retardation, were screened for plasma 7-ketocholesterol level. Individuals with high 7-ketocholesterol level were then analyzed for NPC1 and NPC2 gene mutation to confirm the accuracy of NP-C diagnosis.

Results

By screening the plasma 7-ketocholesterol of suspect individuals, 12 out of 302 (4%) had shown remarkable high levels compared with reference. All these twelve individuals were subsequently confirmed to be NP-C by DNA analysis of NPC1 and NPC2 genes, with the early infantile form (n = 7), the late infantile form (n = 1), the juvenile form (n = 1) and the adult form (n = 1). Furthermore, two NP-C patients without observable neuropsychiatric disability were picked up through this procedure. Only one patient had NP-C due to NPC2 gene mutations, with the rest due to NPC1 gene mutations. We found that in NP-C patients AST was usually mildly elevated and ALT was in a normal range when jaundice was not present. In total, 22 mutant alleles were identified in the NPC1 gene, including six novel small deletions/insertions, e.g., c.416_417insC, c.1030delT, c.1800delC, c.2230_2231delGT, c.2302_2303insG, and c.2795dupA; seven novel exonic point mutations, c.1502A>T (p.D501V), c.1553G>A (p.R518Q), c.1832A>G (p.D611G), c.2054T>C (p.I685T), c.2128C>T(p.Q710X), c.2177G>C (p.R726T), c.2366G>A (p.R789H), and one novel intronic mutation c.2912-3C>G. Small deletions/insertions constituted nearly half of the mutant alleles (10/22, 45%), indicating a unique mutation spectrum in this cohort of Chinese NP-C patients.

Conclusion

Our data confirm in a clinical setting that screening plasma 7-ketocholesterol is an efficient and practical diagnostic tool to identify NP-C patients from suspect individuals. Patients without neuropsychological involvement could also be identified by this method therefore allowing an opportunity for earlier treatment.

[Follow up and gene mutation analysis in cases suspected as 3-methylcrotonyl-coenzyme A carboxylase deficiency by neonatal screening]

OBJECTIVE

3-Methylcrotonyl-coenzyme A carboxylase deficiency (MCCD) is an autosomal recessive inborn error of leucine catabolism. The cases suspected as MCCD detected by neonatal screening are not rare. The aim of the study was to investigate the clinical outcomes in cases suspected as MCCD by neonatal screening. The second aim was to investigate the mutation spectrum of MCC gene in Chinese population and hotspot mutation.

METHOD

Forty-two cases (male 33, female 9) , who had higher blood 3-hydroxy-isovalerylcarnitine (C5-OH) levels(cut-off <0.6 µmol/L) detected by neonatal screening using MS/MS, were recruited to this study during Sept.2011 to Mar.2013. The C5-OH concentrations were [0.84 (0.61-20.15) µmol/L] in 42 cases at the screening recall. Five cases were firstly diagnosed as maternal MCCD, 6 cases as benign MCCD and 31 cases were suspected as MCCD. To follow up the height, weight, mental development, blood C5-OH concentrations and urinary 3-methylcrotonyl-glycine (3-MCG) and 3-hydroxy isovalerate (3-HIVA) in order to investigate the clinical outcome. The MCCC1 and MCCC2 gene mutation were analyzed for some cases. The novel gene variants were evaluated, and the influence of novel missense variants on the protein structure and function were predicted by PolyPhen-2, SIFT, UniProt and PDB software.

RESULT

(1) Forty-two cases had no symptoms, their physical and mental development were normal in the last visit at the median ages of 29 months, the oldest age of follow up was nearly 9 years. (2) Gene mutation analysis was performed for 29 cases with informed consent signed by parents.Fourteen different mutations were identified in 19 cases. The mutations in MCCC1 gene accounted for 86%, the most common mutation was c.ins1680A, (accounted for 40%). Nine kinds of novel variant were detected including 211AG>CC/p.Q74P, c.295G>A/p.G99S, c.764A>C/p.H255P, c.964G>A/p. E322K, c.1331G>A/p.R444H, c.1124delT, c.39_58del20, c.1518delG, c.639+2T>A.Other 3 kinds of mutation in MCCC1 gene and 2 kinds of mutation in MCCC2 gene have been reported previously; the amino acid of mutant positions of five kinds of novel missense variant are almost highly conserved. These missense variants were predicted to cause change of human MCC protein side chain structure by changing hydrogen bonding, size of amino acid residue and electric charge, and predicted to damage the protein function possibly according to PolyPhen-2 and PDB analysis. So these novel variants may be disease-causing mutations. No mutation were detected in 10 cases. (3) Blood concentrations of C5-OH when screening, recall and end of follow-up in maternal MCCD was 3.50 (1.63-11.43), 1.84 (1.00-9.30), 0.27 (0.26-5.81) µmol/L. There was a significant downward trend.In contrast, benign MCCD group was 8.20 (3.60-9.60), 9.67 (3.88-20.15), 23.0 (5.87-49.10) µmol/L.It showed a rising trend. Children's urinary 3-MCG of benign MCCD group was found abnormally elevated in 4 cases (100%) when they were recalled.

CONCLUSION

A certain number of cases with MCCD or suspected as MCCD in this study had no symptoms and normal physical and mental development after follow-up to oldest age of nearly 9 years. The mutation in MCCC1 gene is common, nine novel mutations were found, c.ins1680A may be a hotspot mutation in Chinese population. The urinary GC/MS analysis and blood MS/MS analysis for mother should be routinely performed for all cases with high blood C5-OH level detected by neonatal screening.

Spectrum analysis of common inherited metabolic diseases in Chinese patients screened and diagnosed by tandem mass spectrometry

BACKGROUND

Information concerning inherited metabolic diseases in China is scarce. We investigated the prevalence and age distributions of amino acid, organic acid, and fatty acid oxidation disorders in Chinese patients.

METHODS

Blood levels of amino acids and acylcarnitines (tandem mass spectrometry) were measured in 18,303 patients with suspected inherited metabolic diseases. Diagnosis was based on clinical features, blood levels of amino acids or acylcarnitines, urinary organic acid levels (gas chromatography-mass spectrometry), and (in some) gene mutation tests.

RESULTS

Inherited metabolic diseases were confirmed in 1,135 patients (739 males, 396 females). Median age was 12 months (1 day to 59 years). There were 28 diseases: 12 amino acid disorders (580 patients, 51.1%), with hyperphenylalaninemia (HPA) being the most common; nine organic acidemias (408 patients, 35.9%), with methylmalonic acidemia (MMA) as the most common; and seven fatty acid oxidation defects (147 patients, 13.0%), with multiple acyl-coenzyme A dehydrogenase deficiency (MADD) being the most common. Onset was mainly at 1-6 months for citrin deficiency, 0-6 months for MMA, and in newborns for ornithine transcarbamylase deficiency (OTCD). HPA was common in patients aged 1-3 years, and MADD was common in patients >18 years.

CONCLUSIONS

In China, HPA, citrin deficiency, MMA, and MADD are the most common inherited disorders, particularly in newborns/infants.

[In vitro expression study of novel mutations in phenylalanine hydroxylase gene]

OBJECTIVE

To study the in vitro expression of 6 novel missense mutations (R270G, P275A, F121L, A156P, E183G, I324N) and a previously described R408Q mutation of phenylalanine hydroxylase (PAH) gene and explore the genotype-phenotype correlation through comparison of protein levels and residual enzyme activities.

METHODS

Seven expression vectors containing PAH cDNA were constructed with a site-directed mutagenesis kit. The plasmids were extracted and sequenced to confirm the target mutations. pcDNA3.0 containing PAH cDNA was transfected into COS-7 cells and total proteins were extracted 48 h after transfection. The quantities of proteins and residual enzyme activities of the 7 mutants were assessed with the wild-type PAH gene as reference.

RESULTS

Relative quantities of PAH proteins for R270G, P275A, F121L, A156P, E183G, I324N and R408Q were 10.5%, 56.6%, 54.3%, 8.7%, 8.5%, 67.3% and 85.4%, respectively. The residual enzyme activities were 7.7%, 27.6%, 19.0%, 10.4%, 9.1%, 50.6% and 40.2%, respectively.

CONCLUSION

PAH residual enzyme activities of 7 PAH mutants were all significantly reduced.

[Analysis of clinical manifestations and genetic mutations in a child with Laron syndrome]

OBJECTIVE

To analyze clinical manifestations and gene mutations in a child with severe short stature, explore its molecular mechanism and further clarify the diagnostic procedure for short stature.

METHOD

We observed clinical characteristics of a patient with short stature and did diagnostic examinations, assessed the function of GH-IGF-1 axis, and surveyed its family members.Genomic DNA was extracted from peripheral blood, GHR, IGFALS, STAT5b and GH1 gene were amplified by PCR for sequencing, including exons and splicing areas.

RESULT

The patient presented symmetrical short stature (height -8.2 SDS) and facial features, and other congenital abnormalities.It displayed non-growth hormone deficiency. The baseline value of GH was 21 µg/L, and the peak was 57.9 µg/L. The value of IGF-1 was less than 25 µg/L, and the IGFBP-3 less than 50 µg/L. And IGF-1 generation test showed no response. There was no similar patients in the family members.Sequencing of GHR in the patient revealed a homozygous point mutation (c.Ivs6+1G>A), and her father and mother had the same heterozygous mutation. The same mutation was not identified for her sister.No other candidate gene was found.

CONCLUSION

As the result of combined clinical characteristics and lab examinations, as well as gene detection, the case was diagnosed with Laron syndrome and GHR gene mutation is the molecular mechanism.We should explicit the etiological diagnosis for short stature, and avoid missed diagnosis and misdiagnosis.

Determination of 7-ketocholesterol in plasma by LC-MS for rapid diagnosis of acid SMase-deficient Niemann-Pick disease

Acid sphingomyelinase (ASMase)-deficient Niemann-Pick disease (NPD) is caused by mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene, resulting in accumulation of sphingomyelin in the lysosomes and secondary changes in cholesterol metabolism. We hypothesized that the oxidation product of cholesterol, 7-ketocholesterol (7-KC), might increase in the plasma of patients with ASMase-deficient NPD. In this study, a rapid and nonderivatized method of measurement of plasma 7-KC by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. Plasma samples from healthy subjects, patients with ASMase-deficient NPD, nonaffected ASMase-deficient NPD heterozygotes, Niemann-Pick type C (NPC) disease, glycogen storage disorder type II (GSDII), Gaucher disease (GD), mucopolysaccharidosis type II (MPSII), Krabbe disease (KD), and metachromatic leukodystrophy (MLD) were tested retrospectively. Markedly elevated 7-KC was found in patients with ASMase-deficient NPD and NPC disease that showed significant differences from ASMase-deficient NPD heterozygotes; patients with GSDII, GD, MPSII, KD, and MLD; and normal controls. The analysis of plasma 7-KC by LC-MS/MS offers the first simple, quantitative, and highly sensitive method for detection of ASMase-deficient NPD and could be useful in the diagnosis of both ASMase-deficient NPD and NPC disease.

[Clinical and mutational features of maternal 3-methylcrotonyl coenzyme deficiency]

OBJECTIVE

To report on 5 patients with maternal 3-methylcrotonyl coenzyme A carboxylase deficiency (MCCD) and to confirm the clinical diagnosis through mutation analysis.

METHODS

Five neonates with higher blood 3-hydroxy isovalerylcarnitine (C5-OH) concentration detected upon newborn screening with tandem mass spectrometry and their mothers were recruited. Urinary organic acids were analyzed with gas chromatography mass spectrometry. Gene mutation and protein function analysis were performed by PCR direct sequencing and PolyPhen-2 software.

RESULTS

Higher blood C5-OH concentrations (5.11-21.77 μmol/L) and abnormal 3-hydroxy isovalerate and 3-methylcrotonyl glycine in urine were detected in the five asymptomatic mothers, who were diagnosed as benign MCCD. Higher C5-OH concentration was also detected in their neonates by tandem mass spectrometry, which had gradually decreased to normal levels in three neonates. Four new variations, i.e., c.ins1680A(25%), c.203C > T (p.A68V), c.572T > C (p.L191P) and c.639+5G > T were detected in the MCCC1 gene, in addition with 2 mutations [c.1406G > T (p.R469L, novel variation) and c.592C > T (p.Q198X)]. The novel variations were predicted to have affected protein structure and function.

CONCLUSION

For neonates with higher C5-OH concentration detected upon neonatal screening, their mothers should be also tested to rule out MCCD. Mutations in MCCC1 gene are quite common.

Demographics, diagnosis and treatment of 256 patients with tetrahydrobiopterin deficiency in mainland China: results of a retrospective, multicentre study

BACKGROUND

National coverage of neonatal screening for hyperphenylalaninaemia (HPA) in China is still low and tests to differentiate causes of HPA are not performed in many centres. This study aimed to describe the demographics, geographic distribution, diagnosis, treatment and clinical outcomes of treatment, including intellectual development, in patients with tetrahydrobiopterin (BH4) deficiency in mainland China.

METHODS

This was a retrospective, multicentre, chart review in patients with BH4 deficiency across mainland China born 1985-2010.

RESULTS

Two hundred fifty six patients were included; 59.9 % (267/446) of parents were from eastern China. Median (interquartile range) age at diagnosis decreased from 12.0 (5.5, 102.0) months to 2.0 (1.0, 3.5) months in patients born 1985-1999 (n = 28) and 2005-2010 (n = 152), respectively. 6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency was the primary cause of BH4 deficiency (96.0 %); four hotspot mutations accounted for 76.6 % of PTS gene mutations; two novel variants in the QDPR gene were identified. Most patients (83.6 %) received treatment with BH4, L-dopa, 5-hydroxytryptophan and/or diet therapy. Target blood Phe concentration was confirmed at 88.9 % of visits; median (Q1, Q3) blood Phe concentration was 106.8 (73.0, 120.0) μmol/L during therapy and 117.0 (67.1, 120.0) μmol/L at last visit. Median (Q1, Q3) WISC IQ score was 80.0 (69.0, 90.0) in 33 patients. DQ scores were within normal range (≥85) for 37/59 (62.7 %) patients. Physical development indicators were within normal ranges. Treatment-related adverse events, reported in 20/256 (7.8 %) patients, were mild-to-moderate in severity.

CONCLUSION

This study provides valuable information on the current and historical situation of BH4 deficiency in mainland China.

Impaired glucose tolerance in a mouse model of sidt2 deficiency

Sidt2 was identified as a novel integral lysosomal membrane protein recently. We generated global Sidt2 knockout mice by gene targeting. These mice have a comparatively higher random and fasting glucose concentration. Intraperitoneal and oral glucose tolerance tests in Sidt2 knockout mice indicated glucose intolerance and decreased serum insulin level. Notably, the Sidt2(-/-) mice had hypertrophic islets compared with control mice. By Western blot and immunofluorescence, Sidt2(-/-) mouse islets were shown to have increased insulin protein, which actually contained more insulin secretory granules than their controls, demonstrated by electromicroscopy. Consistent with the in vivo study, isolated islet culture from the Sidt2(-/-) mice produced less insulin when stimulated by a high concentration of glucose or a depolarizing concentration of KCl. Under electromicroscope less empty vesicles and more mature ones in Sidt2(-/-) mice islets were observed, supporting impaired insulin secretory granule release. In conclusion, Sidt2 may play a critical role in the regulation of mouse insulin secretory granule secretion.

[Analysis of GALNS gene mutation in thirty-eight Chinese patients with mucopolysaccharidosis type IVA]

OBJECTIVE

Mucopolysaccharidosis (MPS) type IVA (MPS IVA) is an autosomal recessive lysosomal storage disease caused by deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS) needed to degrade glycosaminoglycanes (GAGs), accumulation of GAGs in the tissue resulting in disorder of function. So far, the small number of articles about clinical study of Chinese MPS IVA were published and only one paper about gene mutation analysis was published. This study aimed to investigate the mutation spectrum and characteristic of GALNS gene in Chinese patients with MPS IVA who were diagnosed in our hospital.

METHOD

Thirty-eight patients from 36 families (male 17, female 21) were diagnosed as MPS IVA by GALNS activity determination [(0.85 ± 1.33) nmol/(17 h·mg)] and clinical symptoms during 2006-2012. The average age of diagnosis was (5.7 ± 3.6) years. Mutation analysis of GALNS gene performed performed by PCR-direct DNA sequencing for 38 patients. PCR-restriction fragment length polymorphism analysis was used for validating novel mutation, and also to assess amino acid conservation for novel missense variants in five different species. PolyPhen-2 tool was used to predict the possible impact of missense mutations on the structure and function of the human GALNS protein, etc. Analysis of GALNS activity and gene mutation in amniotic fluid were performed to provide the prenatal diagnosis for some families with MPS type IVA.

RESULT

(1) Thirty-eight kinds of mutation in GALNS gene were identified in 38 patients of them, 71% were missense mutations. p. M318R was a hot-spot mutation (21%) tested. Five kinds of mutation i.e., p. P163H, p.G168L, p. A324E, p. L366P and p. F452L were only found in Chinese patients with MPS IVA. Eighteen kinds of novel mutation were detected including p. E315K, p.G304D, p.R251Q, p.Y240C, p.G161E, p.N32D, p.L390P, p. D60E, p. P420S, W403C/T404S, p.L454P, for p.W405X, p. M1I, c.409_ c.420del12, c.1176_1178del3, c.1046delG, c.1188delG and IVS9-2A>C. (2) The polymorphism of novel missense variants were ruled out by the PCR-restriction fragment length polymorphism analysis and no related mutations were found in 50 normal controls. A splice site mutation IVS9-2A>C had been validated by reverse transcription PCR direct sequencing. The amino acid of mutant position of 10 kinds of missense variants are highly conserved and only p. L454 is moderately conserved position. These missense variants were predicted to cause damage to the structure and function of human GALNS protein possibly according to the PolyPhen-2 tool, so these novel missense variants may be disease-causing mutations. (3) Prenatal diagnosis was provided for 7 families and three fetuses were diagnosed as MPS IVA.

CONCLUSION

The GALNS gene mutation spectrum in Chinese patients with MPS IVA is really different from that in other countries, five kinds of mutation were only found in Chinese patients with MPS IVA. The reports of hot-spot mutation in Chinese patients were also different, and should be analyzed by more data of gene mutation analysis and epidemiological study.

[Analysis of clinical data and genetic mutations in three Chinese patients with tyrosinemia type I]

OBJECTIVE

To analyze clinical data and gene mutations in 3 Chinese patients with tyrosinemia type I, and to explore the correlation between genotypes and phenotypes.

METHODS

Three patients suspected with tyrosinemia I were tested by tandem mass spectrometry for the level of tyrosine, phenylalanine and succinylacetone in the blood, and by gas chromatography-mass spectrometry to determine the level of succinylacetone and organic acid in their urine. With the diagnosis established, the FAH gene was analyzed with polymerase chain reaction (PCR) and direct sequencing.

RESULTS

Two patients had acute onset of the disease, while another had subacute onset of the disease, with features including hepatomegaly and remarkably increased tyrosine and succinylacetone in the blood. Five mutations were detected in the FAH gene, which included c.455G>A (W152X), c.520C>T (R174X), c.974_976delCGAinsGC, c.1027 G>A (G343R) and c.1100 G>A (W367X), among which c.455G>A (W152X), c.974_976delCGAinsGC and c.1100 G>A (W367X) were not reported previously.

CONCLUSION

Tyrosinemia type I may be effectively diagnosed with the level of tyrosine and succinylacetone by tandem mass spectrometry and succinylacetone in the urine by gas chromatography mass spectrometry. Detection of underlying mutations mutations will be helpful for genetic counseling and further research.

Comparative evaluation of short-term biomarker response to treatment for growth hormone deficiency in Chinese children with growth hormone deficiency born small for or appropriate for gestational age: a randomized phase IV open-label study

OBJECTIVES

To compare the response between Chinese children with growth hormone deficiency (GHD) born either small for gestational age (SGA) or appropriate for gestational age (AGA) after 4 weeks of recombinant human growth hormone (r-hGH) therapy.

METHODS

This was a phase IV, open-label, multicenter, interventional study (NCT01187550). Prepubertal children with GHD received open-label treatment with daily r-hGH (0.033 mg/kg) for 4 weeks. Serum levels of insulin-like growth factor I (IGF-I) and insulin-like growth factor-binding protein 3 (IGFBP3), and metabolic markers (including fasting glucose, insulin, total cholesterol, and homeostasis model assessment of insulin resistance) were assessed at baseline and after 4 weeks of treatment, and were analyzed according to patient subgroup (SGA or AGA).

RESULTS

A total of 205 children with GHD (mean age 10.4 years; 175 AGA, 30 SGA) were included in the analysis. Mean baseline serum IGF-I and IGFBP3 standard deviation scores (SDS) across the whole patient population were lower than the population norms (mean values: -2.1 SDS for IGF-I and -1.2 SDS for IGFBP3), with no significant differences between the two patient subgroups. After 4 weeks, IGF-I and IGFBP3 levels increased by 1.0 SDS (p < 0.001) and 0.34 SDS (p < 0.001), respectively, but no significant differences were found between the two patient subgroups for growth-related or metabolic markers.

CONCLUSIONS

For children with GHD born SGA, IGF-I and IGFBP3 are short-term biomarkers of responsiveness to treatment with growth hormone, as for children with GHD born AGA.

[Outcomes of patients with combined methylmalonic acidemia and homocystinuria after treatment]

OBJECTIVE

Combined methylmalonic acidemia with homocystinuria is a common form of methylmalonic acidemia in China. Patients with this disease can progress to death without timely and effective treatment. This study aimed to analyze the treatment outcomes of patients with combined methylmalonic acidemia and homocystinuria.

METHOD

From September 2004 to April 2012, 58 patients with combined methylmalonic acidemia and homocystinuria (34 males and 24 females) were diagnosed and treated in our hospital. Fifty cases were from clinical patients including 42 early-onset cases and 8 late-onset cases. Their age when they were diagnosed ranged from 18 days to 30.8 years. The other 8 cases were from newborn screening. All the patients were treated with vitamin B12, betaine, folic acid, vitamin B6, and L-carnitine. The physical and neuropsychological development, general laboratory tests, the levels of amino acids, acylcarnitines, and homocysteine in blood, and organic acids in urine were followed up.

RESULT

The follow-up period ranged from 1 month to 7.1 years. Three cases died (all were early-onset cases). In the other patients after treatment, the symptoms such as recurrent vomiting, seizures, lethargy, and poor feeding disappeared, muscle strength and muscle tension were improved, and general biochemical abnormalities such as anemia and metabolic acidosis were corrected. Among the surviving 55 cases, 49 had neurological impairments such as developmental delay and mental retardation. The median levels of blood propionylcarnitine and its ratio with acetylcarnitine, serum homocysteine, and urine methylmalonic acid were significantly decreased (P < 0.01), from 7.73 µmol/L (ranged from 1.5 to 18.61 µmol/L), 0.74 (ranged from 0.29 to 2.06), 97.3 µmol/L (ranged from 25.1 to 250 µmol/L) and 168.55 (ranged from 3.66 to 1032.82) before treatment to 2.74 µmol/L (ranged from 0.47 to 12.09 µmol/L), 0.16 (ranged from 0.03 to 0.62), 43.8 µmol/L (ranged from 17 to 97.8 µmol/L) and 6.81 (ranged from 0 to 95.43) after treatment, respectively.

CONCLUSION

Patients with combined methylmalonic acidemia and homocystinuria respond to a combined treatment consisting of supplementation of hydroxycobalamin, betaine, folic acid, vitamin B6 and L-carnitine with clinical and biochemical improvement. But the long-term outcomes are unsatisfactory, with neurological sequelae in most patients.

[Analysis of propionylcarnitine in blood and methylmalonic acid in urine of 162 patients with methylmalonic acidemia]

OBJECTIVE

To analyze the levels of methylmalonic acid and methylcitrate in urine, propionylcarnitine (C3) in plasma and C3/acetylcarnitine (C2) of patients with methylmalonic acidemia (MMA) and explore their applications in the diagnosis of MMA.

METHODS

From December 2003 to March 2012, a total of 162 patients with MMA (MMA group) and 200 healthy children (control group) of Xinhua Hospital, Shanghai Jiaotong University School of Medicine were recruited. MMA patients with a definite classification were divided into 2 groups: isolate MMA group (n = 51) and MMA complicated with homocysteinemia group (n = 65). Gas chromatography-mass spectrometry was used to measure the urine levels of methylmalonic acid and methylcitrate and tandem mass spectrometry to measure the blood levels of free carnitine (C0), acylcarnitines and methionine (Met).

RESULTS

In the MMA group, the median levels of methylmalonic acid (259.10 (6.73 - 6429.28)), methylcitrate (4.39 (0 - 248.96)), C3 (8.52 (1.50 - 52.11) µmol/L) and C3/C2 (0.73(0.28 - 2.89)) were all higher than the upper limit values (0.2 - 3.6, 0 - 1.1, 0.50 - 4.00 µmol/L and 0.04 - 0.25 respectively). And they were all higher than those in the control group (0 (0 - 1.87), 0.10 (0 - 1.84), 1.40 (0.53 - 3.90) µmol/L, 0.10 (0.04 - 0.23), all P < 0.01). C3/C2 increased significantly in 15 patients while the C3 level remained normal. The median level of Met was normal in the isolate MMA group. But in patients with homocysteinemia, the level of 8.71 (0.68 - 31.95) µmol/L was below the reference value (10.00 - 35.00 µmol/L) and lower than that in the isolate MMA group (15.35 (4.18 - 59.50) µmol/L) and the control group (15.59 (10.20 - 34.68) µmol/L, all P < 0.05).

CONCLUSIONS

Significant increases in the urine level of methylmalonic acid and C3/C2 may be specific to MMA. Organic acid analyses of gas chromatography-mass spectrometry and acylcarnitines with tandem mass spectrometry are required for a definite diagnosis of this disorder. And repeated tests and genomic mutation analysis are necessary for patients with mildly abnormal biochemical indices.

Chromosomal Mapping and QTL Analysis of Resistance to Downy Mildew in Cucumis sativus

Downy mildew of cucumber (Cucumis sativus), caused by Pseudoperonospora cubensis, is a major foliar disease worldwide. The cucumber inbred lines K8 (resistant to downy mildew) and K18 (susceptible) were used to study the inheritance of resistance to downy mildew. Chromosomal mapping of the resistance genes was completed to provide a theoretical basis for the resistance mechanisms and for marker assisted selection (MAS). Inoculation was used to test the level of resistance to P. cubensis in the F₂ and F_2:3 families derived from the cross K8 × K18. Simple sequence repeat (SSR) analysis, combined with bulked segregation analysis (BSA), was done with the DNA of F₂ plants using 2,360 pairs of SSR primers. JoinMap Version 3.0 and MapInspect were used to construct SSR linkages and to verify the relationships between these SSR linkages and cucumber chromosomes. Quantitative trait locus (QTL) analysis of downy mildew resistance was done using MapQTL Version 4.0. Inheritance of resistance to downy mildew in K8 was quantitative. Five QTLs for resistance to downy mildew were detected: dm1.1, dm5.1, dm5.2, dm5.3, and dm6.1. The loci of dm1.1 and dm6.1 were on chromosomes 1 and 6, respectively. The loci of dm5.1, dm5.2, and dm5.3 were on chromosome 5, and were linked. Six linked SSR markers for these five QTLs were identified: SSR31116, SSR20705, SSR00772, SSR11012, SSR16882, and SSR16110. Six and four nucleotide binding site (NBS)-type resistance gene analogs (RGAs) were predicted in the region of dm5.2 and dm5.3, respectively. These results will be of benefit for fine-mapping the major QTLs for downy mildew resistance, and for MAS in cucumber.

Identification of a distinct mutation spectrum in the SMPD1 gene of Chinese patients with acid sphingomyelinase-deficient Niemann-Pick disease

Background

Clinical observations and molecular analysis of the SMPD1 gene in Chinese patients with acid sphingomyelinase deficiency Niemann-Pick disease (NPD) are scarce.

Methods

A cohort of 27 Chinese patients diagnosed with acid sphingomyelinase deficiency, within the past five years, were collected and investigated for genotype, phenotype, and their correlations.

Results

The majority of our patients (25/27) were under 18 years of age. From the cohort group, eight (30%) fulfilled characters of type A. Four other patients experienced neurologic involvement after two years of age, these were classified as intermediate type. The remaining fifteen presented without clear neurologic involvement and were regarded as type B. One patient, from the type B group, presented with the unusual symptom of a secondary amenorrhea. Three patients, one from the type B group and two from the intermediate group, presented with pronounced proteinuria, in the late stages of the disease, indicating possible kidney involvement in NPD. Twenty-four SMPD1 gene mutations had been identified; eighteen of these are novel ones. These included four exonic small deletions/duplications (c.4delC, c.147_150del4, c.842-849dup8, c.1307-1312dup6), one termination mutation (p.Glu248X), and thirteen exonic point mutations (p.Gly336Ser, p.Trp342Cys, p.Leu382Phe, p.Pro429Leu, p.Pro430Ser, p.Trp437Arg, p.Thr451Pro, p.His461Pro, p.Ala484Val, p.Ser486Arg, p.Tyr500His, p.Pro533Leu, p.Val559Leu). Notably, eight mutations had more than one occurrence with c.4delC and p.Glu248X accounting for ~30% of all alleles. Correlation analysis of genotype and phenotype indicated eight mutations, c.842-849dup8, p.Glu248X, p.Arg230Cys, p.Trp437Arg, p.His461Pro, p.Ala484Val p.Ser486Arg, and p.Pro533Leu,to be severe mutations. Five mutations, c.4delC, p.Leu382Phe, p.Pro429Leu, p.Pro430Ser and p.Val559Leu were projected to be mild mutations. Interestingly, three intermediate individuals carried combinations of a mild mutation, c.4delC, on one allele and a severe mutation on the other allele.

Conclusions

The Chinese population may have a comparably high incidence of sphingomyelinase-deficient Niemann-Pick disease type A. This study has identified some novel genotype and phenotype correlations in this rare and devastating disorder.

Application of liquid chromatography-tandem mass spectrometry in the diagnosis and follow-up of maple syrup urine disease in a Chinese population

BACKGROUND

Maple syrup urine disease (MSUD) is an inherited disorder caused by a deficiency of the mitochondrial branched-chain keto acid dehydrogenase complex. We investigated whether liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a more reliable and accurate method than MS/MS in the diagnosis and management of patients with MSUD in a Chinese population.

METHODS

A total of 370 dried blood spots (DBS) from healthy neonates, 44 DBS specimens from phenylketonuria neonates, and 38 DBS samples from 10 MSUD patients were retrospectively tested using the LC-MS/MS method. The results were compared with those obtained by the MS/MS method.

RESULTS

The reference intervals of branched-chain amino acids (BCAAs) and alloiosleucine (Allo-Ile) were estimated for both sexes. In classic MSUD patients, Allo-Ile was markedly elevated (average of 136 μmol/L, which was significantly higher than the normal value, <5 μmol/L). The averages of BCAAs were also markedly elevated continually during the treatment.

CONCLUSIONS

The application of the LC-MS/MS method in the measurement of Allo-Ile and BCAAs in DBS is more useful for diagnosing and managing classic MSUD than the MS/MS method.

NOX, the main regulator in oxidative stress in experimental models of phenylketonuria?

AIM

To reveal the role of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) in the integration of the redox signal in the oxidative molecular regulation mechanism in phenylketonuria (PKU).

METHODS

The blood samples were obtained from Pahenu2-BTBR PKU and wild-type mice, respectively. Phe concentration, total antioxidant capacity (T-AOC), glutathione (GSH) and maleic dialdehyde (MDA) were analyzed. After collection of the mononuclear cells, reverse transcription polymerase chain reaction (RT-PCR) for NOX was performed. In addition, NOX activity and superoxide in mononuclear cells were determined.

RESULTS

Compared to the control group, Phe concentration, T-AOC and MDA were markedly increased in PKU mice (p<0.01, p<0.05, p<0.01, respectively). However, the GSH level in PKU mice was less than that in control group (p<0.05). The mRNA level of subunits of NOX included p47phox and p67phox, were increased in PKU mice (p<0.05), however, the gp91phox had no obvious change in the two groups (p>0.05). NOX activity and superoxide were also remarkably elevated in PKU mice (p<0.05).

CONCLUSION

NOX may play an important role in the integration of the redox signal in the oxidative molecular regulation mechanism in PKU.

[Comparison and clinical application of two methods for determination of plasma chitotriosidase activity]

OBJECTIVE

Chitotriosidase (CT) is a plasma biomarker for Gaucher disease (GD), the enzyme activity is usually markedly elevated in plasma of Gaucher patients, and it was reported that levels of plasma chitotriosidase activity was mildly-moderately increased in patients with Niemann-Pick disease (NPD). The aim of this study was to compare chitotriosidase activity using 4-methylumbelliferyl-β-D-N, N', N″-triacetyl-chitotrioside (4MU-C3) with 4-methylumbelliferyl 4-deoxy-β-D-chitobiose (4MU-4dC2) as substrates, and apply chitotriosidase activity measurement to help clinical determination of GD and NPD, and to monitor therapy in GD patients.

METHOD

Plasma of 45 healthy individuals, 31 patients with GD and 9 patients with NPD type A/B was collected from outpatient clinics of the Department of Pediatric Endocrinologic, Genetic and Metabolic Diseases, Xinhua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine. Plasma chitotriosidase activity was measured with the substrates 4MU-C3 and 4MU-4dC2 respectively. Determinations were based on the methods described by Hollak et al and Rodrigues et al. Meanwhile, common mutation dup24 of the human chitotriosidase gene was detected.

RESULT

(1) Chitotriosidase activity when measured with 4MU-4dC2 gave higher values than 4MU-C3. In the healthy controls chitotriosidase activity was increased 3.7-fold when the 4MU-dC2 was used as substrate as compared with the 4MU-C3 (Z = -4.703, P < 0.001). In the untreated GD patients, the median value was increased 794-fold and 610-fold of the control subjects (Z = -3.823, P < 0.001) when the enzyme was measured with two substrates respectively. In the GD patients during therapy, chitotriosidase activity was increased 134-fold and 79-fold, and after changing therapeutic dose chitotriosidase activity was increased 215-fold and 118-fold of the controls (Z = -2.521, P < 0.05). In the NPD patients chitotriosidase activity was increased 8-fold and 14-fold of the controls (Z = -1.604, P = 0.109). (2) Consistent with the results of chitotriosidase activity, 30 of 85 (35.3%) individuals were homozygotes of dup24 mutation, which are completely chitotriosidase enzyme deficiency. Among GD patients with wild-type and heterozygotes for the dup24 mutation, chitotriosidase activity highly increased in the plasma compared with the controls.

CONCLUSION

The use of 4MU-4dC2 as substrate makes chitotriosidase activity measurement more sensitive. The determination of plasma chitotriosidase activity is a useful tool to assist the clinical identification of Gaucher disease, and to monitor enzyme replacement therapy (ERT) of non-chitotriosidase deficient GD patients. Chitotriosidase activity determination has no value in the clinical identification of NPD.