Department of Medical Biochemistry, School of Medicine, Balikesir University, Balikesir, Turkey.
Department of Medical Biochemistry, Institute of Health Sciences, School of Medicine, Dokuz Eylul University, Izmir, Turkey.
Ann Clin Biochem. 2020 Jul;57(4):291-299. doi: 10.1177/0004563220935140.
Vitamin B12 deficiency frequently appears in phenylketonuria patients having a diet poor in natural protein. The aims of this study were to evaluate vitamin B12 status in phenylketonuria patients by using combined indicator of vitamin B12 status (cB12) as well as methylmalonic acid and homocysteine, more specific and sensitive markers, in comparison with healthy controls.
Fifty-three children and adolescents with phenylketonuria under dietary treatment and 30 healthy controls were assessed cross-sectionally. Serum vitamin B12 and folate concentrations were analysed by chemiluminescence immunoassay. Plasma methylmalonic acid and total homocysteine concentrations were measured by liquid chromatography-tandem mass spectrometry and liquid chromatography, respectively. cB12 was calculated by using a formula involving blood parameters.
Methylmalonic acid and folate concentrations in phenylketonuria group were higher compared with controls. Methylmalonic acid concentrations were high in 56.5% of the patients and 26.7% of the controls with normal vitamin B12 concentrations. Based on cB12, a significant difference within the normal values was detected between the groups. However, although 24.5% of phenylketonuria patients and 13.3% of controls had decreased vitamin B12 status according to cB12, there was no significant difference.
Children and adolescents with phenylketonuria having a strict diet can be at risk of functional vitamin B12 deficiency. This deficiency can be accurately determined by measuring methylmalonic acid concentrations. Calculation of cB12 as a biochemical index did not provide additional information compared with the measurement of methylmalonic acid alone, but may be helpful for classification of some patients with increased methylmalonic acid as having adequate vitamin B12 status.
维生素 B12 缺乏症经常出现在饮食中天然蛋白质含量低的苯丙酮尿症患者中。本研究旨在通过使用维生素 B12 状态综合指标 (cB12) 以及更具体和敏感的甲基丙二酸和同型半胱氨酸标志物来评估苯丙酮尿症患者的维生素 B12 状态，并与健康对照组进行比较。
对 53 名接受饮食治疗的苯丙酮尿症儿童和青少年以及 30 名健康对照者进行横断面评估。采用化学发光免疫分析法检测血清维生素 B12 和叶酸浓度。采用液相色谱-串联质谱法和液相色谱法分别测定血浆甲基丙二酸和总同型半胱氨酸浓度。cB12 通过涉及血液参数的公式计算。
苯丙酮尿症组的甲基丙二酸和叶酸浓度高于对照组。尽管维生素 B12 浓度正常，但仍有 56.5%的患者和 26.7%的对照组的甲基丙二酸浓度升高。根据 cB12 值，两组之间在正常值范围内存在显著差异。然而，尽管根据 cB12 值，24.5%的苯丙酮尿症患者和 13.3%的对照组出现维生素 B12 状态降低，但无统计学差异。
严格饮食的苯丙酮尿症儿童和青少年可能存在功能性维生素 B12 缺乏症。这种缺乏症可以通过测量甲基丙二酸浓度来准确确定。与单独测量甲基丙二酸相比，计算 cB12 作为生化指标并未提供额外信息，但可能有助于将一些甲基丙二酸升高的患者分类为具有足够维生素 B12 状态的患者。
