The utility of methylmalonic acid, methylcitrate acid, and homocysteine in dried blood spots for therapeutic monitoring of three inherited metabolic diseases.

Backgroud: Routine metabolic assessments for methylmalonic acidemia (MMA), propionic acidemia (PA), and homocysteinemia involve detecting metabolites in dried blood spots (DBS) and analyzing specific biomarkers in serum and urine. This study aimed to establish a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous detection of three specific biomarkers (methylmalonic acid, methylcitric acid, and homocysteine) in DBS, as well as to appraise the applicability of these three DBS metabolites in monitoring patients with MMA, PA, and homocysteinemia during follow-up. Methods: A total of 140 healthy controls and 228 participants were enrolled, including 205 patients with MMA, 17 patients with PA, and 6 patients with homocysteinemia. Clinical data and DBS samples were collected during follow-up visits. Results: The reference ranges (25th-95th percentile) for DBS methylmalonic acid, methylcitric acid, and homocysteine were estimated as 0.04-1.02 µmol/L, 0.02-0.27 µmol/L and 1.05-8.22 µmol/L, respectively. Following treatment, some patients achieved normal metabolite concentrations, but the majority still exhibited characteristic biochemical patterns. The concentrations of methylmalonic acid, methylcitric acid, and homocysteine in DBS showed positive correlations with urine methylmalonic acid (r = 0.849, p < 0.001), urine methylcitric acid (r = 0.693, p < 0.001), and serum homocysteine (r = 0.721, p < 0.001) concentrations, respectively. Additionally, higher levels of DBS methylmalonic acid and methylcitric acid may be associated with increased cumulative complication scores. Conclusion: The LC-MS/MS method established in this study reliably detects methylmalonic acid, methylcitric acid, and homocysteine in DBS. These three DBS metabolites can be valuable for monitoring patients with MMA, PA, and homocysteinemia during follow-up. Further investigation is required to determine the significance of these DBS biomarkers in assessing disease burden over time.

Clinical features and ALDH5A1 gene findings in 13 Chinese cases with succinic semialdehyde dehydrogenase deficiency.

BACKGROUND AND AIMS: To investigate the clinical features, ALDH5A1 gene variations, treatment, and prognosis of patients with succinic semialdehyde dehydrogenase (SSADH) deficiency. MATERIALS AND METHODS: This retrospective study evaluated the findings in 13 Chinese patients with SSADH deficiency admitted to the Pediatric Department of Peking University First Hospital from September 2013 to September 2023. RESULTS: Thirteen patients (seven male and six female patients; two sibling sisters) had the symptoms aged from 1 month to 1 year. Their urine 4-hydroxybutyrate acid levels were elevated and were accompanied by mildly increased serum lactate levels. Brain magnetic resonance imaging (MRI) showed symmetric abnormal signals in both sides of the globus pallidus and other areas. All 13 patients had psychomotor retardation, with seven showing epileptic seizures. Among the 18 variants of the ALDH5A1 gene identified in these 13 patients, six were previously reported, while 12 were novel variants. Among the 12 novel variants, three (c.85_116del, c.206_222dup, c.762C > G) were pathogenic variants; five (c.427delA, c.515G > A, c.637C > T, c.755G > T, c.1274T > C) were likely pathogenic; and the remaining four (c.454G > C, c.479C > T, c.1480G > A, c.1501G > C) were variants of uncertain significance. The patients received drugs such as L-carnitine, vigabatrin, and taurine, along with symptomatic treatment. Their urine 4-hydroxybutyric acid levels showed variable degrees of reduction. CONCLUSIONS: A cohort of 13 cases with early-onset SSADH deficiency was analyzed. Onset of symptoms occurred from 1 month to 1 year of age. Twelve novel variants of the ALDH5A1 gene were identified.

Dual rare genetic diseases in five pediatric patients: insights from next-generation diagnostic methods.

BACKGROUND: Clinicians traditionally aim to identify a singular explanation for the clinical presentation of a patient; however, in some cases, the diagnosis may remain elusive or fail to comprehensively explain the clinical findings. In recent years, advancements in next-generation sequencing, including whole-exome sequencing, have led to the incidental identification of dual diagnoses in patients. Herein we present the cases of five pediatric patients diagnosed with dual rare genetic diseases. Their natural history and diagnostic process were explored, and lessons learned from utilizing next-generation diagnostic technologies have been reported. RESULTS: Five pediatric cases (3 boys, 2 girls) with dual diagnoses were reported. The age at diagnosis was from 3 months to 10 years. The main clinical presentations were psychomotor retardation and increased muscular tension, some accompanied with liver dysfunction, abnormal appearance, precocious puberty, dorsiflexion restriction and varus of both feet, etc. After whole-exome sequencing, nine diseases were confirmed in these patients: Angelman syndrome and Krabbe disease in case 1, Citrin deficiency and Kabuki syndrome in case 2, Homocysteinemia type 2 and Copy number variant in case 3, Isolated methylmalonic acidemia and Niemann-Pick disease type B in case 4, Isolated methylmalonic acidemia and 21-hydroxylase deficiency in case 5. Fifteen gene mutations and 2 CNVs were identified. Four novel mutations were observed, including c.15292de1A in KMT2D, c.159_164inv and c.1427G > A in SLC25A13, and c.591 C > G in MTHFR. CONCLUSIONS: Our findings underscore the importance of clinicians being vigilant about the significance of historical and physical examination. Comprehensive clinical experience is crucial for identifying atypical clinical features, particularly in cases involving dual rare genetic diseases.

Case report: An asymptomatic mother with an inborn error of cobalamin metabolism (cblC) detected through high homocysteine levels during prenatal diagnosis.

Background: The most common disorder of the intracellular cobalamin metabolism pathway is the combined methylmalonic acidemia and homocysteinemia, cblC type (cblC). There is a variation in its clinical spectrum ranging from severe neonatal-onset forms that are highly fatal to later-onset forms which are milder. In this study, the first case of an asymptomatic Chinese woman with a defect in congenital cobalamin (cblC type) metabolism at prenatal diagnosis due to elevated homocysteine level is identified. Case presentation: The proband, a male child born to a 29-year-old G1P0 mother, admitted to local hospital with feeding disorder, intellectual disability, seizures, microcephaly, as well as heterophthalmos. The level of the urine methylmalonic was elevated. Equally found were increased blood propionylcarnitine (C3) and propionylcarnitine/free carnitine ratio (C3/C0) and decreased methionine levels. The plasma total homocysteine level was elevated at 101.04 µmol/L (normal < 15 µmol/L). The clinical diagnosis of combined methylmalonic acidemia and homocysteinemia was supported. Four years later, the mother of the boy married again and came to us for prenatal diagnosis exactly 15 weeks after her last menstrual period. Subsequently, there is an increase in the amniotic fluid methylmalonate. The level of the amniotic fluid total homocysteine was marginally high. A considerably elevated amniotic fluid C3 was equally observed. In addition, there is a respective significant increase in the plasma and urine total homocysteine at 31.96 and 39.35 µmol/L. After the sequencing of MMACHC genes, it is found that the boy, a proband carried a homozygous mutation of the MMACHC at c.658_660delAAG. While the boy's mother, she carries two mutations in MMACHC: c.658_660delAAG and c.617G>A. The fetus is a carrier of the MMACHC gene. Following the administration of routine treatment, the mother remained symptom-free in the course of pregnancy, and she gave birth to a healthy boy. Conclusion: Variable and nonspecific symptoms characterized the cblC type of methylmalonic acidemia combined with homocysteinemia. Both biochemical assays and mutation analysis are recommended as crucial complementary techniques.

Visible-Light-Promoted Direct C3-H Cyanomethylation of 2H-Indazoles.

The efficient visible-light-promoted cyanomethylation of 2H-indazoles in the presence of Ir(ppy)3 as the photocatalyst and bromoacetonitrile as the cyanomethyl radical source was achieved under mild conditions, providing a series of C3-cyanomethylated derivatives in good yields.

Late-onset cblC deficiency around puberty: a retrospective study of the clinical characteristics, diagnosis, and treatment.

BACKGROUND: cblC deficiency is the most common type of methylmalonic aciduria in China. Late-onset patients present with various non-specific symptoms and are usually misdiagnosed. The purpose of this study is to investigate the clinical features of patients with late-onset cblC deficiency and explore diagnosis and management strategies around puberty. RESULTS: This study included 56 patients (35 males and 21 females) with late-onset cblC deficiency who were admitted to our clinic between 2002 and September 2021. The diagnosis was confirmed by metabolic and genetic tests. The clinical and biochemical features, disease triggers, outcome, and associated genetic variants were examined. The onset age ranged from 10 to 20 years (median age, 12 years). Fifteen patients (26.8%) presented with symptoms after infection or sports training. Further, 46 patients (82.1%) had neuropsychiatric diseases; 11 patients (19.6%), cardiovascular diseases; and 6 patients (10.7%), pulmonary hypertension. Renal damage was observed in 6 cases (10.7%). Genetic analysis revealed 21 variants of the MMACHC gene in the 56 patients. The top five common variants detected in 112 alleles were c.482G > A (36.6%), c.609G > A (16.1%), c.658_660delAAG (9.8%), c.80A > G (8.0%), and c.567dupT (6.3%). Thirty-nine patients carried the c.482G > A variant. Among 13 patients who exhibited spastic paraplegia as the main manifestation, 11 patients carried c.482G > A variants. Six patients who presented with psychotic disorders and spastic paraplegia had compound heterozygotic c.482G > A and other variants. All the patients showed improvement after metabolic treatment with cobalamin, L-carnitine, and betaine, and 30 school-aged patients returned to school. Two female patients got married and had healthy babies. CONCLUSIONS: Patients with late-onset cblC deficiency present with a wide variety of neuropsychiatric symptoms and other presentations, including multiple organ damage. As a result, cb1C deficiency can easily be misdiagnosed as other conditions. Metabolic and genetic studies are important for accurate diagnosis, and metabolic treatment with cobalamin, L-carnitine, and betaine appears to be beneficial.

[Factors affecting phenotypes in the patients with MMACHC gene c.609G>A homozygous variant cblC type methylmalonic acidemia combined with homocysteinuria].

OBJECTIVE: To investigate the factors affecting phenotypes in the patients of methylmalonic acidemia combined with homocysteinemia cblC type with MMACHC c.609G>A homologous variant. METHODS: A retrospective study on the clinical manifestations, complications, treatment, and outcome in 164 patients of cblC type with MMACHC c.609G>A homologous variant was conducted. The patients were diagnosed by biochemical and genetic analysis from January 1998 to December 2020. RESULTS: Among the 164 patients, 2 cases were prenatally diagnosed and began treatment after birth. They are 3 and 12 years old with normal physical and mental development. Twenty-one cases were diagnosed by newborn screening. Among them, 15 cases had with normal development. They were treated from the age of two weeks at the asymptomatic period. Six cases began treatment aged 1 to 3 months after onset. Their development was delayed. One hundred and forty-one cases were clinically diagnosed. Their onset age ranges from a few minutes after birth to 6 years old. 110 cases had early-onset (78.0%). 31 cases had late-onset (22.0%). Five of them died. 24 patients lost to follow-up. Of the 141 clinically diagnosed patients, 130 (92.2%) with psychomotor retardation, 69 (48.9%) with epilepsy, 39 (27.7%) with anemia, 30 (21.3%) had visual impairment, 27 (19.1%) had hydrocephalus, 26 (18.4%) had feeding difficulties, 7 (5.0%) with liver damage, and 5 (3.5%) with metabolic syndrome. The frequency of hydrocephalus and seizures was significantly higher in the early-onset group. The urinary methylmalonic acid increased significantly in the patients with epilepsy. During the long-term follow-up, the level of plasma total homocysteine in the seizure-uncontrolled group was significantly higher than that in the seizure-controlled group, the difference had a statistical significance (P<0.05). CONCLUSION: Most of the patients with MMACHC c.609G>A homozygous variant had early-onset disease, with a high mortality and disability rate. If not treated in time, it will lead to neurological damage, resulting in epilepsy, mental retardation, hydrocephalus, and multiple organ damage. Pre-symptomatic diagnosis and treatment are crucial to prevent irreversible neurological damage. Neonatal screening and prenatal diagnosis are important to improve the outcome of the patients.

Comparing amniotic fluid mass spectrometry assays and amniocyte gene analyses for the prenatal diagnosis of methylmalonic aciduria.

BACKGROUND: Methylmalonic aciduria (MMA), a rare inherited disorder, is the most common organic aciduria in China, and prenatal diagnosis has contributed to its prevention. However, the prenatal diagnosis of MMA using cultured amniocytes or chorionic villi to detect gene mutations is exclusively applicable to families with a definite genetic diagnosis. To evaluate the reliability of mass spectrometry assays for the prenatal diagnosis of MMA, we conducted a retrospective study of our 10 years' experience. MATERIALS AND METHODS: This retrospective compare study reviewed the medical records for maternal and fetuses data for 287 mothers with a family history of MMA from June 2010 to December 2020. Methylmalonate and propionylcarnitine in cell-free amniotic fluid were measured using a stable isotope dilution method (GC/MS) and MS/MS-based method (LC/MS/MS). Total homocysteine (tHcy) was measured by fluorescence polarization immunoassay. Depending on the presence of disease-causing gene mutations in probands, gene studies on amniocytes from 222 pregnant women were performed. RESULTS: For 222 fetuses of the families with definite genetic diagnosis, gene analyses were performed using cultured amniocytes. 52 fetuses were affected by MMA, whereas 170 were "unaffected". For GC/MS and LC/MS/MS, the specificity was 96.5% and 95.9%, sensitivity was 71.2% and 84.6%, respectively. The positive and negative predictive values were 86.0% and 91.6% and 86.3% and 95.3%, respectively. Propionylcarnitine/butyrylcarnitine ratio showed the highest accuracy and could thus serve as a sensitive indicator to identify those at a risk for MMA. When GC/MS and LC/MS/MS were performed in parallel, the specificity was 92.5% and sensitivity was 95.6%. When evaluating tHcy, the positive and negative predictive values were 95.0% and 96.1%, respectively. In 65 fetuses without family genetic diagnosis, 11 were finally confirmed to have MMA and 54 were "unaffected" by amniotic fluid biochemical assays. The 54 children showed normal urine organic acids and healthy development after birth. CONCLUSIONS: Amniotic fluid biochemical assays using GC/MS and LC/MS/MS in parallel increased the accuracy of prenatal diagnosis of MMA. Propionylcarnitine is a more reliable marker than methylmalonic acid in amniotic fluid. Further, tHcy is recommended for the prenatal diagnosis of combined MMA and homocysteinemia.

Analysis of the relationship between phenotypes and genotypes in 60 Chinese patients with propionic acidemia: a fourteen-year experience at a tertiary hospital.

BACKGROUND: Propionic acidemia is a severe inherited metabolic disorder, caused by the deficiency of propionyl-CoA carboxylase which encoded by the PCCA and PCCB genes. The aim of the study was to investigate the clinical features and outcomes, molecular epidemiology and phenotype-genotype relationship in Chinese population. METHODS: We conducted a retrospective study of 60 Chinese patients diagnosed at Peking University First Hospital from 2007 to 2020. Their clinical and laboratory data were reviewed. The next-generation sequencing was conducted on blood samples from 58 patients. RESULTS: Only 5 (8.3%) patients were identified by newborn screening. In the rest 55 patients, 25 had early-onset (≤ 3 months) disease and 30 had late-onset (> 3 months) disease. Neurological abnormalities were the most frequent complications. Five cases detected by newborn screening had basically normal development. Nine (15%) cases died in our cohort. 24 patients (41.4%) harbored PCCA variants, and 34 (58.6%) harbored PCCB variants. 30 (11 reported and 19 novel) variants in PCCA and 28 (18 reported and 10 novel) variants in PCCB mere identified. c.2002G>A and c.937C>T in PCCA, and c.838dupC in PCCB were the most common variants in this cohort, with the frequency of 13.9% (6/44 alleles), 13.9% (6/44 alleles) and 12.5% (8/64 alleles), respectively. There was no difference in clinical features and outcomes between patients with PCCA and PCCB variants. Certain variants with high frequencies and homozygotes may be associated with early-onset or late-onset propionic acidemia. CONCLUSIONS: Although the genotype-phenotype correlation is still unclear, certain variants seemed to be related to early-onset or late-onset propionic acidemia. Our study further delineated the complex clinical manifestations of propionic acidemia and expanded the spectrum of gene variants associated with propionic acidemia.

Analysis of 70 patients with hydrocephalus due to cobalamin C deficiency.

OBJECTIVE: To analyze the clinical characteristics of patients with hydrocephalus secondary to cobalamin C (cblC) deficiency and to discuss the optimal strategies for assessing and treating such patients by performing clinical and laboratory studies in 70 patients. METHODS: A total of 1,211 patients were clinically diagnosed with methylmalonic acidemia (MMA) from 1998 to 2019. Among them, cblC deficiency was confirmed in 70 patients with hydrocephalus by brain imaging and biochemical and genetic analysis. RESULTS: Of the 70 patients, 67 (95.7%) had early-onset MMA and homocystinuria. The patients typically had high blood propionylcarnitine and total homocysteine, low methionine, and methylmalonic aciduria. Signs of intracranial hypertension were relatively rare. We measured ventricular dilatation early in the disease by cranial ultrasound and MRI and/or CT. Eighteen different MMACHC mutations, including 4 novel mutations (c.427C>T, c.568insT, c.599G>A, and c.615C>A), were identified biallelically in all 70 patients. c.609G>A was the most frequent mutation, followed by c.658_660del, c.217C>T, and c.567dupT. Three cases were diagnosed by postmortem study. Metabolic therapy, including cobalamin injections supplemented with oral l-carnitine and betaine, was administered in the remaining 67 cases. A ventriculoperitoneal shunt was performed in 36 cases. During the follow-up, psychomotor development, nystagmus, impaired vision, and sunset eyes improved gradually. CONCLUSION: Hydrocephalus is a severe condition with several different causes. In this study, ventriculomegaly was found in 70 patients with cblC deficiency. Early diagnosis, etiologic treatment, and prompt surgical intervention are crucial to improve the prognosis of patients.

Variable phenotypes and outcomes associated with the MMACHC c.609G>A homologous mutation: long term follow-up in a large cohort of cases.

BACKGROUND: Cobalamin C deficiency (cblC) caused by the MMACHC mutations is the most common type of the disorders of intracellular cobalamin metabolism. While the c.609G > A mutation is most frequent in Chinese cblC patients, its correlation with phenotype has not been delineated. Here we aim to investigate the factors affecting variable phenotypes and outcomes associated with the MMACHC c.609G > A homologous mutation in 149 Chinese cases to have implications for treatment and prevention. METHODS: We assessed 149 cblC patients caused by MMACHC c.609G > A homozygous mutation. The clinical manifestations, complications, treatment, and outcomes were evaluated; 120 patients were followed-up till December 2019. RESULTS: Two patients (1.3%) were prenatally diagnosed, treated after birth and consequently showed normal development. In 15 patients (10.1%) detected by newborn screening, 10 were treated at the age of 2 weeks and showed normal development, while the other 5 were treated after onset and showed neurologic disorders. All 132 clinically diagnosed patients (88.6%) developed symptoms at age from few minutes after birth to 72 months. Among them, 101 (76.5%) had early-onset (before the age of 12 months) and 31 (23.5%) had late-onset (after the age of 12 months). Totally 5 patients died and 24 were lost to follow-up. Of the 132 clinical diagnosed patients, 92 (69.7%) presented with developmental delay, 65 (49.2%) had seizures, 37 (28.0%) had anemia, 24 (18.2%) had feeding difficulty, 23 (17.4%) had ocular problems, and 22 (16.7%) had hydrocephalus. Compared with the non-developmental delay group, the onset age, the age at treatment initiation and the time from onset to treatment initiation were later in the developmental delay group. Seizure group showed significantly higher urinary methylmalonic acid concentration. During long-term follow-up, plasma total homocysteine (tHcy) levels were significantly higher in patients in the uncontrolled group than those in the seizure-free group. CONCLUSIONS: Most cblC patients caused by MMACHC c.609G > A homozygous mutation showed early-onset. The clinically diagnosed patients usually showed the presence of irreversible brain disorders. Patients treated from the pre-symptomatic stage showed favorable outcomes. Therefore, newborn screening, prenatal diagnosis and early treatment are crucial and the c.609G > A mutant allele should be listed in the pre-pregnancy carrier screening panel in China.

Eleven novel mutations and clinical characteristics in seven Chinese patients with thiamine metabolism dysfunction syndrome.

Thiamine metabolism dysfunction syndrome (THMD) comprises a group of clinically and genetically heterogeneous encephalopathies with autosomal recessive inheritance. Four genes, SLC19A3, SLC25A19, SLC19A2, and TPK1, are associated with this disorder. This study aimed to explore the clinical, biochemical and molecular characteristics of seven Chinese patients with THMD. Targeted next-generation sequencing of mitochondrial DNA and nuclear DNA was used to identify the causative mutations. The patients presented with subacute encephalopathy between the ages of 1-27 months. Brain magnetic resonance imaging (MRI) revealed abnormalities in the basal ganglia, indicating Leigh syndrome. Urine α-ketoglutarate in five patients was elevated. In four patients, five novel mutations (c.1276_1278delTAC, c.265A > C, c.197T > C, c.850T > C, whole gene deletion) were found in SLC19A3, which is associated with THMD2. In two patients, four novel mutations (c.194C > T, c.454C > A, c.481G > A, and c.550G > C) were identified in SLC25A19, supporting a diagnosis of THMD4. In one patient, two novel mutations (c.395T > C and c.614-1G > A) were detected in TPK1, which is indicative of THMD5. The patients received thiamine, biotin, and symptomatic therapy, upon which six patients demonstrated clinical improvement. Our findings expanded the phenotypic and genotypic spectrum of THMD, with eleven novel mutations identified in seven Chinese patients. Early diagnosis and treatment have a significant impact on prognosis.

Reduced 24-h Sodium Excretion Is Associated With a Disturbed Plasma Acylcarnitine Profile in Vasovagal Syncope Children: A Pilot Study.

Objective: To investigate if the low sodium intake is associated with the plasma carnitine and acylcarnitine profile in children with vasovagal syncope (VVS). Materials and Methods: Twenty-six children suffering from VVS were recruited in the present study and divided into a group of low urinary sodium excretion or a group of normal urinary sodium excretion according to the excretion of 24-h urinary sodium <3 or 3-6 g, respectively. The excretion of 24-h urinary sodium was detected with ion-selective electrode approach. Plasma carnitine and acylcarnitine concentrations were measured with tandem mass spectrometry. Each participant completed the head-up tilt test. The demographics, clinical characteristics, hemodynamic parameters and plasma carnitine and acylcarnitine concentrations were compared between the two groups. A bivariate correlation between plasma acylcarnitine profiles and the excretion of 24-h urinary sodium was conducted with Spearman's correlation coefficients. Results: Of the enrolled VVS patients, 14 patients were assigned to the group of low urinary sodium excretion and the remaining 12 patients were assigned to the group of normal urinary sodium excretion. Symptoms of fatigue were more prevalent in the group of low urinary sodium excretion than in the group of normal urinary sodium excretion (p = 0.009). Aside from fatigue, no other differences in the demographics, clinical characteristics or hemodynamic parameters during the head-up tilt test were found between the two groups (p > 0.05). Concentrations of plasma tiglylcarnitine (C5:1), hydroxyhexadecanoylcarnitine (C16OH), hydroxyoctadecanoylcarnitine (C18OH), and carnitine C22 were significantly higher in the group of low urinary sodium excretion than in the group of normal urinary sodium excretion (all p-values = 0.048); moreover, they were all negatively correlated with 24-h urinary sodium levels (all p-values = 0.016). There were no differences between the two groups in other acylcarnitines or free carnitine. Conclusions: Reduced excretion of 24-h urinary sodium is associated with a disturbed plasma acylcarnitine profile in children with VVS. The findings suggest that restricted sodium intake-induced disturbance of plasma acylcarnitines and related cellular energy metabolism might be involved in the pathogenesis of VVS in children.

A study on a cohort of 301 Chinese patients with isolated methylmalonic acidemia.

Methylmalonic acidemia (MMA) is the most common organic acidemia in China. This study aimed to characterise the genotypic and phenotypic variabilities, and the molecular epidemiology of Chinese patients with isolated MMA. Patients (n = 301) with isolated MMA were diagnosed by clinical examination, biochemical assays, and genetic analysis. Fifty-eight patients (19.3%) were detected by newborn screening and 243 patients (80.7%) were clinically diagnosed after onset. Clinical onset ranged from the age of 3 days to 23 years (mean age = 1.01 ± 0.15 years). Among 234 MMA patients whose detailed clinical data were available, 170 (72.6%) had early onset disease (before the age of 1 year), and 64 (27.4%) had late-onset disease. The 234 MMA patients manifested with neuropsychiatric impairment (65.4%), haematological abnormality (31.6%), renal damage (8.5%), and metabolic crises (67.1%). Haematological abnormality was significantly more common in early-onset patients than that in late-onset patients. The incidence of metabolic crises was significantly high (P < 0.001) in patients with mut type than those with other types of isolated MMA. Variations (n = 122) were identified in MMUT, MMAA, MMAB, MMADHC, SUCLG1, and SUCLA2, of which 45 were novel. c.729_730insTT was the most frequent MMUT mutation, with a significantly higher frequency in our patients than that in 151 reported European patients. The frequency of c.914T>C in MMUT in our cohort was also higher than that in 151 European patients. MMUT mutations c.729_730insTT and c.914T>C are specific for the Chinese population. Our study expanded the spectrum of phenotypes and genotypes in isolated MMA.

One potential hotspot ACADVL mutation in Chinese patients with very-long-chain acyl-coenzyme A dehydrogenase deficiency.

Very long-chain acyl-coenzyme A dehydrogenase deficiency (VLCAD deficiency), a rare autosomal recessive disorder, is characterized by hypoketotic hypoglycemia, cardiomyopathy, liver damage, and myopathy. VLCAD deficiency is caused by defects of ACADVL gene, which encodes VLCAD protein. The aim of this study was to determine the clinical, biochemical, prognosis and mutation spectrum of patients with VLCAD deficiency in mainland China. A total of Six families visited us, four patients (2 boys and 2 girls) were admitted in hospital due to liver dysfunction, hypoglycemia, and positive newborn screen result. The parents of the other two patients (2 girls) visited us for genetic consultation after their children's death. All the six patients had elevated level of serum tetradecenoylcarnitine (C14:1-carnitine), four of them showed decreased free carnitine (C0) level, and three had dicarboxylic aciduria. Eight types of mutations of the ACADVL gene were detected, three of them are novel, including c.563G > A (p.G188D) c.1387G > A (p.G463R) and c.1582_1586del (p.L529Sfs*31). The p.R450H mutation accounts for 9/52 alleles (5/40 in previous study of 20 unrelated patients, and 4/12 in this study) of genetically diagnosed Chinese VLCAD deficiency cases. The four alive patients (Patient 1-4) responded well to diet prevention and drug therapy with stable hepatic dysfunction condition. In conclusion, we describe three novel mutations of the ACADVL gene among six unrelated families with VLCAD deficiency. Moreover, we suggest that the p.R450H may be a potential hotspot mutation in the Chinese population.

Eight novel mutations detected from eight Chinese patients with isovaleric acidemia.

BACKGROUND: Isovaleric acidemia (IVA), a rare autosomal recessive disorder in leucine metabolism caused by defected IVD gene, is characterized by episodes of acute metabolic crisis and psychomotor development retardation. This study aimed to determine the clinical, biochemical, and mutation spectrum of patients with IVA from mainland China. METHODS: Eight patients (three boys and five girls) from eight unrelated families were collected, IVD gene mutations and phenotypes were examined. RESULTS: The patients were admitted because of vomiting, feeding difficulty, psychomotor retardation and "dirty sock" odor. Elevated blood isovaleryl (C5)-carnitine and urine isovalerylglycine were detected from all our patients. Fourteen mutations of the IVD gene were detected, eight of them are novel, c.145C>T (p.Q49Ter), c.359G>A (p.R120Q), c.424C>T (p.R142C), c.458T>C (p.L153P), c.466-1G>T, c.676_677insA (p.T226Nfs*13), c.1039G>A (p.A347T) and c.1076A>G (p.D359G). With this study, a total of 34 alleles were studied in the Chinese population. c.1208A>G (p.Y403C), the common mutation in Taiwan, accounts for 9/34 alleles (7 in previous reports and 2 in this study). CONCLUSIONS: We described eight novel mutations detected from eight unrelated Chinese patients and provided evidence to support that the p.Y403C is the hotspot mutation in this population.

Mutation Hot Spot Region in the HOGA1 Gene Associated with Primary Hyperoxaluria Type 3 in the Chinese Population.

BACKGROUND: Primary hyperoxaluria type 3 (PH3) is a rare autosomal recessive disorder that affects glyoxylate metabolism. PH3 is caused by defects in 4-hydroxy-2-oxoglutarate aldolase, which is encoded by the HOGA1 gene. However, only 3 cases of PH3 have been described in Asians until today. This study aimed to determine the clinical and mutation spectra of patients from mainland China with PH3. METHODS: We applied targeted next-generation sequencing to four non-consanguineous, unrelated Chinese families with PH3 to identify the genes hosting disease-causing mutations. This approach was confirmed by Sanger sequencing. RESULTS: Five patients (2 boys and 3 girls) from four unrelated Chinese families were admitted because of kidney stones. Five HOGA1 gene sequence mutations were detected, including two novel mutations, c.811C>T (p.R271C) and c.812G>A (p.R271H). These compound heterozygous mutations were detected in a female PH3 patient (patient 4). Other patients included 2 boys who had heterozygous c.834_834+1GG>TT and c.834G>A (p.A278A) mutations (patients 1 and 2), a girl with homozygous c.834G>A (p.A278A) mutation (patient 3), and a girl with heterozygous c.834_834+1GG>TT and c.346C>T (p.Q116X) mutations (patient 5). The mutations in the c.834_834+1 region, including c.834G>A, c.834+1G>T, and c.834_834+1GG>TT, account for 5/8 of alleles in our study and 3/4 of alleles reported among Chinese patients. All patients in this study received hyperhydration and urine alkalinization treatment. CONCLUSION: Five PH3 cases were reported. Potential mutation hot spot region (c.834_834+1) in the Chinese population and two novel mutations were found.

Medium-chain acyl-coenzyme A dehydrogenase deficiency: Six cases in the Chinese population.

BACKGROUND: Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD) is a rare autosomal recessive disorder that affects the degradation of medium-chain fatty acids. Few cases of MCADD have been documented to date in mainland China. METHODS: Medium-chain acyl-coenzyme A dehydrogenase deficiency was diagnosed in six patients (three girls and three boys) from six unrelated Chinese families at ages ranging from 10 days to 3 years old. The diagnosis was confirmed by the identification of a primary biomarker of serum octanoyl-carnitine (C8) and genetic pathogenic mutations. RESULTS: Only two patients were admitted because of vomiting, diarrhea, myasthenia, and coma; the other four patients were diagnosed via the newborn screening process. Six mutations were found in acyl-CoA dehydrogenase medium chain (ACADM). One mutation (c.727C>T) was novel and the others (c.158G>A, c.387+1delG, c.449_452del, c.1045C>T, and c.1085G>A) have been previously reported. CONCLUSIONS: Six Chinese cases of MCADD were identified. One novel mutation was found. c.449_452del and c.1085G>A were common mutations in this study.

Patients with cobalamin G or J defect missed by the current newborn screening program: diagnosis and novel mutations.

Cobalamin G (cblG) and cobalamin J (cblJ) defects are rare disorders of cbl metabolism caused by MTR and ABCD4 mutations, respectively. Patients with atypical biochemical features can be missed by current newborn screening using tandem mass spectrometry (MS/MS), in which total homocysteine (tHCY) in dried blood spots (DBS) is not a primary biomarker. Two Chinese patients suspected of cbl defect but missed by newborn screening were studied. Using comprehensive metabolic analyses including MS/MS assay for tHCY in DBS, slightly low methionine in Patient 1, methymalonic aciduria in Patient 2, and homocysteinemia in both patients were detected, and DBS tHCY of two patients were obviously elevated (59.22 µmol/L, 17.75 µmol/L) compared to 140 healthy controls (2.5th-97.5th percentile, 1.05-8.22 µmol/L). Utilizing whole-exome sequencing, we found two novel MTR variants c.871C>T (p.Pro291Ser) and c.1771C>T (p.Arg591*) in Patient 1, and a ABCD4 homozygous variant c.423C>G (p.Asn141Lys) in Patient 2. Our study identified the first cblG patient and cblJ patient in mainland China, and highlighted comprehensive metabolic analyses and genetic tests in patients suspected of cbl defects. It also indicated that supplementary MS/MS assay for tHCY in DBS may be practical for early diagnosis of homocysteinemia, without repeated blood sampling.

Mutations of MACF1, Encoding Microtubule-Actin Crosslinking-Factor 1, Cause Spectraplakinopathy.

As a member of spectraplakin family of cytoskeletal crosslinking proteins, microtubule-actin crosslinking factor 1 (MACF1) controls cytoskeleton network dynamics. Knockout of Macf1 in mice resulted in the developmental retardation and embryonic lethality. Spectraplakinopathy type I, a novel neuromuscular condition characterized by periodic hypotonia, lax muscles, joint contracture, and diminished motor skill, was reported to be associated with heterozygous genomic duplication involving the MACF1 loci, with incomplete penetrance and highly variable clinical presentation in a single pedigree. In this study, parental-derived compound heterozygous novel missense mutations of MACF1, c.1517C>T (p.Thr506Ile) and c.11654T>C (p.Ile3885Thr), were found to co-segregate with disease status in two affected brothers presenting with progressive spastic tetraplegia, dystonia, joint contracture, feeding difficulty and developmental delay. We speculated that MACF1 mutations cause spectraplakinopathy inherited in an autosomal recessive manner. Our clinical findings expanded the phenotype of this neuromuscular disorder and provided new insights into the function of MACF1.