H. Wick

Rapid differential diagnosis of carboxylase deficiencies and evaluation for biotin-responsiveness in a single blood sample

We have developed a method for rapid differential diagnosis of isolated or multiple deficiencies of the 3 mitochondrial biotin-dependent carboxylases: propionyl-CoA (PCC), 3-methylcrotonyl-CoA (MCC) and pyruvate carboxylase (PC), and for simultaneous evaluation of biotin-responsiveness using a single blood sample. Lymphocytes were isolated from heparinized blood and preincubated without and with 10(-5) mol/l biotin in medium before determination of PCC, MCC and PC activities. Plasma was used for estimation of biotin concentration and biotinidase activity. A definitive diagnosis could be made in 7 of 9 patients studied up to now: 4 patients suffered from biotin-nonresponsive isolated PCC-deficiency, and 3 patients from biotin-responsive multiple carboxylase deficiency caused by deficient biotinidase activity. In two patients, a carboxylase deficiency was excluded. These results were confirmed in studies using fibroblasts. In addition, a simple method for detection of deficiency in holocarboxylase synthesis is described.

Biotinidase deficiency: a cause of subacute necrotizing encephalomyelopathy (Leigh syndrome). Report of a case with lethal outcome.

ABSTRACT: An unusual clinical course of a patient with biotinidase deficiency, causing Leigh syndrome, is reported. Laryngeal stridor was the major presenting symptom followed by progressive neurologic deterioration and death at the age of 21.5 mo. Absence of skin and hair abnormalities as well as of organic aciduria delayed the correct diagnosis. Necropsy revealed subacute necrotizing encephalopathy (Leigh syndrome). Carboxylase activities (propionyl CoA carboxylase, 3-methylcrotonyl-CoA carboxylase, pyruvate carboxylase) measured in lymphocytes 1 day before death were decreased to 10% of normal values. Propionyl-CoA carboxylase was shown to be the only stable carboxylase in human postmortem tissue; in our patient it was moderately decreased in postmortem liver (29% of control) and kidney (42%), but severely decreased in brain (3%). These findings might explain the severity of neurological symptoms in the absence of marked organic aciduria. They indicate that in biotinidase deficiency the CNS may become biotin depleted earlier and more severely than other organs. Biotinidase deficiency should be included in the differential diagnosis of Leigh syndrome and of unexplained respiratory problems.

Five patients with a biotin-responsive defect in holocarboxylase formation : Evaluation of responsiveness to biotin therapy in vivo and comparative biochemical studies in vitro

Biochemical studies in five patients with a defect in biotin-responsive holocarboxylase synthesis are reported. The age of onset (2 d to 6 y) as well as the severity of illness varied considerably. In all patients diagnosis was established by the finding of organic aciduria typical for multiple carboxylase deficiency in a catabolic state. In four patients the response to biotin therapy was evaluated by measurement of mitochondrial carboxylase activities in lymphocytes and by monitoring urinary organic acid excretion. In three patients clinical symptoms disappeared with 10-20 mg biotin/d, whereas normalization of the biochemical parameters required higher doses (20-40 mg/d). The fourth patient required a dose of 100 mg biotin/d before her skin rash disappeared. She remains mentally retarded and shows slightly elevated urinary organic acid excretion. Carboxylase activities were clearly deficient in fibroblasts grown in the commonly used medium which contains 10 nmol/L biotin (contributed by FCS in medium) in two patients. Fibroblasts of the other three patients became deficient only in a low biotin medium (0.1 nmol/L). Reactivation of deficient carboxylase activities in relation to time and biotin concentration correlated well with the severity and age of onset of illness in four patients. In one patient, however, carboxylase reactivation followed a more complex pattern requiring the longest incubation time but only a moderately increased biotin concentration of 19 nmol/L compared with 3-5 nmol/L in normal cells and 34-4000 nmol/L in the other four patients. The results in the five patients are in accordance with a primary defect of holocarboxylase synthetase due to a decreased affinity for biotin, in one patient combined with a decreased Vmax.

Biotinidase Deficiency Associated with Renal Loss of Biocytin and Biotin

Clinical and biochemical investigations in six patients with congenital biotinidase deficiency are presented. The time course of biotin depletion in relation to carboxylase activities and clinical onset of symptoms was studied after withdrawal of biotin supplementation. Renal biotin clearance studies were performed in patients and controls. Renal loss of biocytin and biotin itself are shown to be a major cause for the increased biotin requirement in patients with congenital biotinidase deficiency.

Biotinidase Deficiency: Factors Responsible for the Increased Biotin Requirement

Inability to recycle biotin from endogenous biocytin in congenital biotinidase deficiency is associated with increased requirement of exogenous free biotin. We have observed that severe biotin depletion with clinical and biochemical consequences occurs within 12 days after birth in a newborn patient and within 15–20 days after withdrawal of biotin supplementation in four other patients. Our studies have shown that:(1)Urinary loss of biotin and biocytin are major causes for this rapid biotin depletion.(2)Intestinal absorption of biotin seems to be normal at least at the loading dose of 1.5 µg/kg.(3)At normal or subnormal plasma biotin concentrations biocytin is found in low concentrations (below 1 nmoll−1) in plasma of patients but at much higher concentrations in urine (100–600 nmoll−1).(4)An oral load of biocytin results in patients in unchanged biotin levels but in a marked rise of biocytin in plasma followed by rapid renal excretion of biocytin whereas in controls biotin levels in plasma increase rapidly and biocytin remains below detection levels.

Comparison of patients with complete and partial biotinidase deficiency: Biochemical studies

SummarySeventeen partially biotinidase-deficient patients detected by neonatal screening or family studies were compared with four patients with classical biotinidase deficiency. Using a sensitive HPLC method for biotinidase in plasma (substrate: biocytin) the patients could be divided into two groups: one with residual biotinidase activity, and the second with undetectable biotinidase activity (0-activity). Biocytin excretion, characteristically elevated in 0-activity patients, decreased rapidly with increasing residual biotinidase activity and was almost normal when residual activity exceeded 2–3% of mean normal. In one patient with classical disease (0-activity) biotin deficiency, typical organic aciduria and multiple carboxylase deficiency were found as early as at the second week of life. In contrast, 13 infants with residual activities from 1.2% to 23% had no remarkable clinical or biochemical abnormalities. However, in three 5-, 14- and 15-year-old healthy siblings with residual biotinidase activities between 2.3% and 4.2%, biotin deficiency was proven by decreased activities of the mitochondrial carboxylases in lymphocytes (30–57% of mean normal) and, in the older siblings, also by subnormal plasma biotin concentrations. In biotinidase deficiency, biotin depletion presumably occurs earlier in the brain than in other tissues and may thus first affect the central nervous system. For this reason and because of discrete biochemical abnormalities found in a patient with residual biotinidase activity of 8%, we suggest that at least all patients with residual activities below 10% should be treated with biotin.

Late-onset holocarboxylase synthetase-deficiency: pre- and post-natal diagnosis and evaluation of effectiveness of antenatal biotin therapy

Abstract The clinical and biochemical findings in a family with late-onset holocarboxylase synthetase (HCS) deficiency are described. The index patient had two life-threatening episodes of metabolic decompensation at the age of 13 and 18 months with ketotic hypoglycaemia, vomiting and progressive loss of consciousness. The child recovered without biotin therapy. Organic aciduria characteristic of multiple carboxylase deficiency (MCD) was found, however, the key metabolites were only slightly elevated in some samples. Biotinidase deficiency was considered but excluded by the finding of normal plasma biotinidase activity. The correct diagnosis was made only at the age of 19 months when severe MCD was found in lymphocytes in the presence of normal plasma biotin concentration. HCS deficiency was confirmed by fibroblast studies. Biotin therapy (20 or 40 mg/day) prevented further episodes and normalized biochemical parameters with so far normal development.During two subsequent pregnancies, 10 mg biotin/day was administered to the mother from the 20th week of gestation. At delivery plasma biotin in cord blood samples was 3–4 times higher than in maternal plasma. The 2nd child was unaffected. In the 3rd pregnancy prenatal diagnosis was performed at 16 weeks of gestation. The concentration of methylcitrate in amniotic fluid was within the normal range and that of 3-hydroxyisovalerate only slightly elevated. However, enzyme assays in cultured amniotic fluid cells were consistent with an affected fetus. At birth, carboxylase activities in lymphocytes of this newborn were only moderately decreased to 37% of mean normal. HCS deficiency was confirmed postnatally in fibroblasts. Development remains normal on biotin therapy (20 mg/day). Conclusion Prenatal diagnosis in families with milder forms of HCS deficiency has to be performed by enzyme assays in cultured amniotic cells since organic acid analysis of amniotic fluid may be inconclusive in affected fetuses. Biotin administered prenatally is effectively taken up by the fetus and prevents functional deficiency of the carboxylases in an affected newborn.

Quantitative determination of biocytin in urine of patients with biotinidase deficiency using high-performance liquid chromatography (HPLC)

A specific method for the quantitative determination of biocytin from urine of biotinidase deficient patients is described using HPLC-separation and quantitative determination by an avidin binding method. Partial purification of biocytin from urine was achieved with an anion exchange resin and concentration of the eluate by lyophilization. The recovery of biocytin from urines was 95.3 +/- 5.9 (mean +/- SD). The precision of biocytin estimation in patients urines including the HPLC-sample preparation procedure varied between 5.9% and 10.5% (CV). Biocytin concentrations were measured in urine samples of 5 patients obtained during and/or before biotin therapy. Before treatment biocytin excretion ranged from 6.2-28.8 nmol/mmol creatinine. During therapy biocytin excretion increased to the 1.3 to 4-fold level in 3 out of 4 patients. However, there was no dose-related increase of biocytin excretion when pharmacological doses were administered. Apart from biocytin and biotin, patients excrete additional biotin derivatives. Some of these have been preliminary identified as bisnorbiotin and oxidation products of bisnorbiotin, biocytin and biotin.

Comparison of Folic Acid Coenzyme Distribution Patterns in Patients with Methylenetetrahydrofolate Reductase and Methionine Synthetase Deficiencies

ABSTRACT: Folic acid coenzyme distribution patterns were examined in the liver and kidney of two patients with homocystinuria due to different inborn errors of metabolism affecting the remethylation of homocysteine to methionine. One patient, with severe mental retardation (and death at 3½ yr), had greatly reduced levels of methylenetetrahydrofolic acid (THF) reductase in fibroblasts as well as in liver and kidney. Chromatographic separation of folate coenzymes in liver showed an abnormal pattern with THF as the main component and almost no methyl-THF but total folate was normal. The other patient, who was dystrophic, microcephalic, and had megaloblastic anemia died at age 4 months. He had reduced levels of methionine synthetase in liver and kidney due to a defect of intracellular cobalamin metabolism. Chromatographic analysis of his tissues showed methyl-THF to be the principal principal folate form and a markedly reduced total folate. These results support the “methyl-THF trap” hypothesis and offer information with respect to the possible therapy of these two disorders.

Low biotinidase activity in plasma of some preterm infants: possible source of false-positive screening results

Screening for biotinidase deficiency has been added recently to some national screening programmes. To clarify the problem of false-positive screening tests in premature infants, we have studied biotinidase activities in the plasma of this population in more detail. In 64 newborns (premature and term babies) biotinidase activities correlated positively with gestational age from the 2nd to the 30th day of life. During the 1st–3rd day the activities were below the normal adult range in all 64 infants. In 56 infants the activities subsequently increased gradually and reached the normal adult range during the 4th–40th day of life. In contrast, the biotinidase activities in eight preterm infants dropped during the 3rd–7th day of life. Impaired liver function as a possible cause for this finding could be ruled out in these infants. The lowest activities in these infants were measured during the 4th–6th day of life, i.e. unfortunately at a time when samples for the screening are normally taken. According to our data, 4–8 out of 48 preterm or small-for-date infants with biotinidase activities ranging from 4.7%–26% of the mean adult value would have given false-positive screening tests. A positive screening test was also obtained in a newborn and in an older unrelated child with a partial biotinidase deficiency. In these children the biotinidase activity did not rise but remained slightly below or at the lower range for heterozygotes (at 31% and 38% of the mean adult value). Currently we do not know whether such individuals are heterozygotes, or whether they have a variant of biotinidase deficiency. However, these children have developed normally without biotin therapy.