异戊酸血症一例临床及异戊酰辅酶A脱氢酶基因突变研究

目的 了解异戊酸血症患儿的临床、实验室特点以及异戊酰辅酶A脱氢酶(IVD)基因突变情况.方法 对1例异戊酸血症患儿的病史、实验室检查以及血串联质谱和尿气相色谱质谱结果进行了分析,对IVD基因12个外显子及两端内含子行PCR扩增和DNA测序,限制性内切酶片段长度多态性分析c.466G＞C(G127A)新突变.结果 患儿男,2岁7个月,生后3 d起出现呕吐和酸中毒,行幽门切开术后仍反复呕吐,伴有酸中毒发作,智力发育明显落后.血串联质谱分析显示C5酰基肉碱水平增高至12.89μmol/L,尿气相色谱质谱分析显示异戊酰甘氨酸明显升高,临床诊断为异戊酸血症.IVD基因DNA测序显示,患儿存在复合杂合突变:c.149G＞A(R21H)和c.466G＞C(G127A),c.466G＞C(G127A)突变在IVD基因第5外显子上,是以往未报道的新突变.结论 报道1例异戊酸血症,新生儿期发病,反复呕吐,酸中毒和智力落后,血C5酰基肉碱明显升高,尿中有异戊酰、甘氨酸大量排出,基因诊断发现1个IVD基因新突变.     

Glycine therapy in isovaleric acidemia

The therapeutic efficacy of oral glycine was tested in a 3-year-old girl with isovaleric acidemia. An oral leucine load (25 mg/kg) caused a rise of the blood levels of isovaleric, lactic, and pyruvic acids as well as an increase of urinary excretion of the ketone bodies. These changes did not occur when oral glycine (250 mg/kg) was given with the leucine. Glycine supplementation favored the formation of isovalerylglycine, a nontoxic conjugate of isovaleric acid which is excreted rapidly. Excretion of isovalerylglycine rose threefold when leucine and glycine were administered simultaneously. Chronic glycine therapy was tolerated well and may have prevented one episode of ketoacidosis.     

新生儿期异戊酸血症3例诊治与随访

目的探讨新生儿期异戊酸血症的预防与治疗方法。方法分析3例异戊酸血症新生儿的临床发病特点、随访结果以及目前治疗情况,评估异戊酸血症的预后。结果经过新生儿疾病筛查确诊并规范治疗后,其中2例患儿目前发育基本正常,生化结果稳定。另一例患儿随着年龄增大,饮食控制较难管理,其发育水平仍出现下降。结论异戊酸血症需要早期确诊,新生儿疾病筛查为早期诊断此病的重要方法,规范治疗并且配合综合康复训练有助于改善患者预后。     

Phenotypic and mutation spectrums of Thai patients with isovaleric acidemia

Background: Isovaleric acidemia (IVA) is an autosomal recessive disorder caused by deficiency of isovaleryl‐CoA dehydrogenase (IVD). Clinical features include vomiting, lethargy, metabolic acidosis, and “sweaty feet” odor. The pathognomonic metabolite, isovalerylglycine, is detected on urine organic acid analysis. Clinical diagnosis of IVA can be confirmed on mutation analysis of the IVD gene. Methods: The cases of five unrelated Thai patients with IVA, identified on urine organic acid analysis, are described. Mutation analysis of the IVD gene was performed using polymerase chain reaction sequencing of the entire coding regions. Results: Four out of the five IVA patients had an acute neonatal form. The hematologic abnormalities were common and thus could be presenting symptoms in the absence of metabolic acidosis. As for the neurological outcome, only one patient had normal intelligence. Mutation analysis of the IVD gene identified the mutations c.457–3_2CA>GG, c.1199A>G (p.Y371C), c.281C>G (p.A65G), c.358G>A (p.G91R), and c.827T>C (p.L247P). The poor outcome in most patients might be explained by the delayed diagnosis and initial unavailability of the metabolic formulas and medications in Thailand. The c.457–3_2CA>GG mutation was identified in all of the present patients. This suggests that it is the most common mutation in the Thai population. Therefore, it could be a founder mutation in Thai subjects. One of the present Thai IVA patients also had the p.Y371C mutation, which is common in Han Chinese subjects. In addition, two novel mutations, p.A65G and p.L247P, were identified. Conclusion: The present study provides additional knowledge on the genotype–phenotype of IVA, suggesting that IVD mutations in Asian populations are distinct from these in Western populations.     

Therapeutic effects of glycine in isovaleric acidemia.

The effect of glycine administration on acute leucine loading (125 mg/kg) was tested in a patient with isovaleric acidemia. Serum isovaleric acid at 1-3/4 hr after the leucine loading alone was elevated to 5.60 mg/100 ml and urinary isovaleryglycine excretion was 9.90 mg/mg creatine/24 hr. Whe the same amount of leucine was given with glycine (250 mg/kg) serum isovaleric acid was only 0.93 mg/200 ml. Unfortunately, urine was collected for only 12 hr after the leucine-glycine loading. However, the amount of urinary isovaleryglycine was 26.2 mg/mg creatine in this period. In the following experiments in which a meal containing 80 mg leucine/kg was given, serum isovaleric acid was elevated to 1.14 and 1.01 mg/100 ml at 3 hr and 6 hr after the loading, respectively. How-ever, serum isovaleric acid was only 0.53 and 0.79 mg/100 ml at 3 and 6 hr, respectively, when the identical mean was given with 2 g glycine. The effect of long term glycine administration (250 mg/kg/24 hr) was also tested. It did not prevent two ketotic episodes which were caused by infections. However, the duration of clinical symptoms such as vomiting and a large anion gap in the acute episodes were much shorter with rectal glycine administration. The patient's linear growth and weight gain durin glycine administration was much better than that in the pretreatment period.     

Fanconi syndrome in a patient with a variant of isovaleric acidemia

Fanconi syndrome with proximal renal tubular acidosis is caused by a variety of anatomic, functional and metabolic disorders. We report a patient with a variant of isovaleric acidosis who developed proximal tubular acidosis. This patient was able to acidify the urine during metabolic acidosis, developed a hyperchloremic metabolic acidosis, and needed 24 mEq/kg/day of bicarbonate to maintain normal serum bicarbonate. She had a FE Bicarbonate of 12 +/- 4% during bicarbonate infusion. Isovaleric acidosis may be another toxic cause of proximal RTA.     

Isovaleryl-CoA dehydrogenase activity in isovaleric acidemia fibroblasts using an improved tritium release assay

Isovaleric acidemia is a disorder of leucine metabolism caused by a deficiency of isovaleryl-CoA dehydrogenase. At least two clinical subgroups of patients exist: a severe form, in which symptoms occur within the 1st wk of life, and a milder variant in which manifestations develop later in life. We developed a modified version of the tritium release assay to accurately measure residual isovaleryl-CoA dehydrogenase activity in fibroblasts from patients with both forms of isovaleric acidemia. In the modified assay, specific isovaleryl-CoA dehydrogenase-catalyzed tritium release from [2,3-3H]isovaleryl-CoA was determined by including an inhibitor of isovaleryl-CoA dehydrogenase, (methylenecyclopropyl)acetyl-CoA, in one of the tubes in paired assays, to determine the nonspecifically released 3H2O. Residual activities of the nine isovaleric acidemia lines tested ranged from 0 to 0.67 pmol 3H2O/min/mg protein (controls 19.4 +/- 8.0). The three lines from mildly affected individuals all had no detectable activity, whereas the severe cases had a mean of 0.41 pmol 3H2O/min/mg protein. Normal human fibroblast isovaleryl-CoA dehydrogenase had a Km for isovaleryl-CoA of 22 microM, with a Vmax of 51 pmol 3H2O/min/mg protein. The Ki of isovaleryl-CoA dehydrogenase by (methylenecyclopropyl)acetyl-CoA was approximately 2 microM.     

Methylmalonic acidemia mimicking diabetic ketoacidosis in an infant

Methylmalonic acidemia (MMA) is an inherited organic acidemia usually present with recurrent episodes of acute illness. A typical episode is ushered in with ketonuria and vomiting, followed by acidosis, dehydration, and lethargy, leading, in the absence of aggressive treatment, to coma and death. We report an infant with MMA presented with diabetes symptoms. A 13-month-old girl complained of polydipsia, diuresis, and loss of weight. She had clinical signs of diabetic ketoacidosis such as dehydration, deep sighing respiration, smell of ketones, lethargy, and vomiting. Laboratory analysis showed hyperglycemia with acidosis and ketonuria. She was treated with parenteral fluid, electrolyte, and insulin infusion. Two days after her discharge, after having a meal rich in protein, she was brought unconscious with hepatomegaly, severe acidosis, ketonuria, and mild hyperammonemia. The absence of hyperglycemia and the presence of neurologic findings suggested organic acidemia. MMA was diagnosed because of methylmalonic aciduria and elevated C3 carnitine esters. Cranial magnetic resonance imaging (MRI) showed increased uptake of radiocontrast material in the basal ganglia bilaterally. A homozygous mutation in exon 4 of the MMAA gene was found in mutation analysis and confirmed the diagnosis of cblA-deficient MMA. Neurologic regression was improved with treatment of low-protein diet, vitamin B12, and l-carnitine. In patients born to consanguineous parents who admit during infancy with severe acidosis refractory to treatment, organic acidemias should be kept in mind, even they have high blood glucose. The definitive diagnosis is important because it may allow a specific treatment and a favorable evolution to prevent the sequelae.     

4-Hydroxyisovaleric acid: A new metabolite in isovaleric acidemia

In addition to N-isovalerylglycin, isovaleric, 3-hydroxyisovaleric and methylsuccinic acids the excretion of previously unreported 4-hydroxyisovaleric acid in isovaleric acidemia is described. The new metabolite seems to be an intermediate product in the formation of methylsuccinic acid from isovaleric acid by omega-oxidation.Parts of this paper have been presented during a poster session at the International Symposium on Inborn Errors of Metabolism in Humans in Interlaken/Switzerland in September 1980     

Neonatal form of isovaleric acidemia. Apropos of a new case

The case reported concerns a 18 day-old girl who was hospitalized for severe toxemia. The nauseous smell, and significant ketonuria led us to suspect a disorder in amino-acids metabolism. Diagnosis was proven by gas chromatography. With adequate diet, evolution was favourable and the child had a normal psycho-motor development.     

Endogenous catabolism is the major source of toxic metabolites in isovaleric acidemia

A patient with isovaleryl-coenzyme A dehydrogenase deficiency was given a synthetic oral feed containing L-(2H3-methyl)-leucine of high isotopic purity as the only dietary precursor to the defective enzyme. Metabolites derived from this source were readily distinguished from their unlabeled endogenous counterparts by mass spectrometry. During 6 consecutive days of labeled leucine ingestion, the average daily excretion of labeled metabolites was only about 10% of the total derived from leucine. It is suggested that therapy should be directed toward the control of endogenous protein turnover rather than the restriction of dietary protein intake.     

The identification and the excretion pattern of isovaleryl glucuronide in the urine of patients with isovaleric acidemia

We identified isovaleryl glucuronide in the urine of patients with isovaleric acidemia by using gas chromatography-mass spectrometry (GC-MS) and by identifying the products of enzymatic hydrolysis. Conjugation of isovaleryl-CoA with glycine, by the action of glycine-N-acylase, is the main detoxification mechanism in isovaleric acidemia. The identification of isovaleryl glucuronide demonstrates a hitherto unknown, additional detoxification mechanism in patients with isovaleric acidemia. Quantitative analysis of 72 urine specimens from four patients with isovaleric acidemia shows that isovaleryl glucuronide is more likely to be excreted when the amount of urinary 3-hydroxyisovaleric acid excretion is high. This suggests that detoxification via glucuronide conjugation plays an important role when the glycine conjugation system is saturated.     

营养不良导致甲基丙二酸尿症合并同型半胱氨酸血症患儿皮肤损害

<正>患儿,男,2个月,因喂养困难、精神不振1月余,皮肤溃烂10 d而就诊。患儿生后3 d出现精神萎靡、嗜睡、食量减少、黄疸。当地医院检查胸片见双肺内带散在点片状阴影。头颅CT提示脑白质密度减低。     

<Emphasis Type="Italic">N</Emphasis>-carbamylglutamate treatment for acute neonatal hyperammonemia in isovaleric acidemia

Hyperammonemia occurs mainly in patients with branched-chain organic acidemias such as propionic, methylmalonic, and isovaleric acidemias. Its pathophysiological process is mainly via the competitive inhibition of N-acetylglutamate synthetase. Oral carglumic acid (N-carbamylglutamate) administration can correct hyperammonemia in neonates with propionic and methylmalonic acidemias, thus avoiding dialysis therapy. Isovaleric acidemia is an autosomal recessive disease of leucine metabolism due to deficiency of isovaleryl-CoA dehydrogenase. For the first time, we report a neonate with isovaleric acidemia, whose plasma ammonia concentration dropped dramatically after one oral load of carglumic acid. This experience suggests that carglumic acid could be considered for acute hyperammonemia resulting from isovaleric acidemia. However, trials with more patients are needed.     

Dietary therapy in two patients with vitamin B12-unresponsive methylmalonic acidemia

The biochemical and therapeutic responses to dietary therapy were studied in a 25-month-old girl and a 1-month-old girl with methylmalonic acidemia (MMA-emia), which was unresponsive to vitamin B₁₂.The minimum daily intake of protein which patients could tolerate and display a good development was between 1.0 and 1.2 g per kg body weight. Supplementation with amino acid mixture devoid of toxic amino acids was required to prevent protein malnutrition when daily protein intake was restricted to 0.6 g per kg body weight. Caloric intake should be sufficient, not only to promote growth but also to prevent a rise in MMA level, especially when a patient has ketoacidosis.It was found that MMA excretion per mg creatinine in random urine specimens correlated significantly with serum MMA and twenty four-hour output of MMA per kg body weight. Therefore measurement of MMA in a single urine specimen is useful for evaluating the in vivo accumulation of MMA.     

Glutaric acidemia, type I, missed by newborn screening in an infant with dystonia following promethazine administration

We report a child initially diagnosed with promethazine-induced dystonia despite a lack of response to diphenhydramine therapy. On further evaluation, the child was diagnosed with glutaric acidemia, type I (GA-I), an autosomal recessive inborn error of metabolism caused by the deficiency of glutaryl-CoA dehydrogenase. The characteristic clinical feature of GA-I is an acute encephalopathic and neurologic crisis typically occurring during a catabolic state. Despite slow improvement, many patients do not fully recover from a neurologic crisis, and residual neurologic morbidity can be significant. Although newborn screening using tandem mass spectrometry is expected to enable presymptomatic diagnosis of GA-I, this patient was not detected by newborn screening with tandem mass spectrometry. Therefore, a high suspicion of GA-I must be maintained in the evaluation of childhood dystonia, even when newborn screening results are reportedly normal.