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Mitochondrial acetoacetyl-CoA thiolase (T2) deficiency is an inborn error of metabolism that affects isoleucine catabolism and ketone body metabolism. We identified 7 novel and 2 previously reported mutations in six T2-deficient patients. Transient expression analysis of wild-type and eight mutant cDNAs was performed at 40, 37 and 30 degrees C. Although no significant residual activity was detected, mutant proteins were detected in the N158D, N158S, R208Q, Y219H and N282H mutants. Accumulation of these mutant proteins was temperature-sensitive with the highest expression levels at lower temperatures. Expression of Q73P and N353K cDNAs yielded neither residual T2 protein nor enzyme activity. An E252del mutant T2 was detected with a relative protein amount and enzyme activity of 30% and 25%, respectively, in comparison to the wild-type at 37 degrees C. The E252del mutant protein was more stable at 30 degrees C expression than 37 degrees C, but was essentially undetectable at 40 degrees C, indicating its temperature-sensitive instability. Kinetic studies revealed a twofold K(m) elevation for substrates coenzyme A and acetoacetyl-CoA in the E252del mutant, while V(max) was comparable to the wild-type. We conclude that the E252del is a temperature-sensitive K(m) mutant. This correlates well with the effect predicted from the T2 tertiary structure analysis, using the crystal structure of the human T2 homotetramer. The probable effect of the other mutations on the T2 tertiary structure was also evaluated.

Six subjects with classical phenylketonuria (PKU) were treated with large neutral amino acid supplements (PreKUnil, Nilab, Dk) at 0.4g/kg/day in equally divided doses three times each day on an increased natural protein diet. All six subjects had low or deficient blood concentrations of both tyrosine and tryptophan, which are precursors for dopamine and serotonin, respectively, at the beginning of the study and were increased substantially throughout the study. Blood phenylalanine concentrations remained essentially unchanged, while the brain phenylalanine concentrations gradually decreased toward the carrier range as seen in parents of children with PKU. Two subjects were diagnosed with clinical depression and were in counseling programs at initiation of the study. At the end of the study all patients reported increased energy and overall improvement in well-being.

For pregnant women with phenylketonuria (PKU), maintaining blood phenylalanine (Phe)360μmol/L is critical due to the toxicity of elevated Phe to the fetus. Sapropterin dihydrochloride (sapropterin) lowers blood Phe in tetrahydrobiopterin (BH4) responsive patients with PKU, in conjunction with a Phe-restricted diet, but clinical evidence supporting its use during pregnancy is limited. As of June 3, 2013, the Maternal Phenylketonuria Observational Program (PKU MOMS) sub-registry contained data from 21 pregnancies - in women with PKU who were treated with sapropterin either before (N=5) or during (N=16) pregnancy. Excluding data for spontaneous abortions (N=4), the data show that the mean of median blood Phe [204.7±126.6μmol/L (n=14)] for women exposed to sapropterin during pregnancy was 23% lower, and had a 58% smaller standard deviation, compared to blood Phe [267.4±300.7μmol/L (n=3)] for women exposed to sapropterin prior to pregnancy. Women on sapropterin during pregnancy experienced fewer blood Phe values above the recommended 360μmol/L threshold. When median blood Phe concentration was360μmol/L throughout pregnancy, 75% (12/16) of pregnancy outcomes were normal compared to 40% (2/5) when median blood Phe was360μmol/L. Severe adverse events identified by the investigators as possibly related to sapropterin use were premature labor (N=1) and spontaneous abortion (N=1) for the women and hypophagia for the offspring [premature birth (35w4d), N=1]. One congenital malformation (cleft palate) of unknown etiology was reported as unrelated to sapropterin. Although there is limited information regarding the use of sapropterin during pregnancy, these sub-registry data show that sapropterin was generally well-tolerated and its use during pregnancy was associated with lower mean blood Phe. Because the teratogenicity of elevated maternal blood Phe is without question, sapropterin should be considered as a treatment option in pregnant women with PKU who cannot achieve recommended ranges of blood Phe with dietary therapy alone.