The natural history of untreated phenylketonuria over 20 years

Fifty-one adults with untreated phenylketonuria (PKU), have been reviewed after a 20 year interval, at ages ranging from 28.8 to 71.8 years. Five died of causes unrelated to PKU. Three severely affected individuals had shown a progressive loss of motor function and three had developed epilepsy, bringing the total with this problem to 12. No loss of abilities was apparent in 41 patients. Other health problems, including cataracts, were not frequent. Serum phenylalanine levels had decreased over the 20 year period. Untreated PKU does not generally cause progressive loss of abilities during adult life.     

Diet and phenylketonuria: time for change?

This article is a report of a meeting of dietitians held on 15 September 1992 in Birmingham to discuss the recommendations of a 'Medical Research Council Working Party on the Dietary Management of Phenylketonuria'. (Contributions on the day of the meeting came from Judith Houghton, Eleanor Weetch, Isabel Smith, Sheena Laing, Ruth Watling, John Walter, Rodney Pollitt.)     

母亲苯丙酮尿症后代的脑MRI表现

目的 提高对母亲苯丙酮尿症(MPKU)后代脑MRI表现的认识。资料与方法 报告2例生化及临床检查证实为MPKU双胞胎的．MRI改变，并复习文献。结果 文中2例表现与文献报道不一致．与苯丙酮尿症患儿的表现相似。常规T2WI及FLAIR均显示室周白质、侧脑室三角区、半卵圆中心条片状高信号。弥散加权成像(DWI)除更清楚地显示上述改变外，尚显示双侧内囊后肢及胼胝体压部信号增高。结论 常规T2WI及FIJAIR上可显示MPKU后代脑白质异常，DWI可提供更多诊断依据。     

Clinical consequences of heterozygosity for autosomal-recessive diseases*,**

Heterozygotes of autosomal-recessive diseases can often be recognized by special heterozygote tests, since enzyme activities are normally reduced in comparison with the normal homozygote state. In Drosophila, the majority of recessive lethal mutations shows a reduction of fitness in heterozygotes, whereas in a strong minority fitness of heterozygotes is increased. This review will be devoted to a consideration of the extent to which heterozygotes for a wide variety of nominally recessive diseases are subject either to an increased liability for common diseases or slight shifts of behavioral characteristics. The available evidence has been collected and will be discussed in three steps: Most studies are available for phenylketonuria. For this group of diseases, a slight reduction of average--especially verbal--I.Q. in heterozygotes has been reported together with signs of a slightly increased cerebral irritability, a possible slight increase of risk for mental disease, and an increase of blood phenylalanine levels in stress situations. The PKU example is used to discuss methodological problems involved in such studies. Other conditions for which relevant deviations in heterozygotes are possible or even likely include among others lipid storage diseases, microcephaly, myoclonus epilepsy, Wilson's disease, galaktokinase deficiency, homocystinuria, recessive myotonia and ataxia- teleangiectasia (increased cancer risk). Since heterozygotes for autosomal recessive diseases are common, it is possible that an appreciable fraction of "multifactorial" genetic liabilities for common, "constitutional" or mental disease might simply be due to heterozygosity for genes whose homozygous affects are already well known. By the same token, much of the "normal" genetic variability influencing cognitive performance (I.Q.)--especially in the lower range--and personality characteristics could also be caused by recessive genes in the heterozygous state.     

三个新的PAH基因短串联重复序列多态性及其在苯丙酮尿症产前诊断中的应用

目的提高经典型苯丙酮尿症的产前诊断的成功率。方法在苯丙氨酸羟化酶（phenylalanine hydroxylase，PAH）基因附近选择了3个新的短串联重复序列（short tandem repeat，STR）位点（PAH26、PAH32和PAH9），进行扩增长度片段多态性分析，确定它们在中国人群的分布及在诊断中的应用价值。结果3个新的STR位点的多态信息含量分别为0．518（PAH26）、0．413（PAH32）和0．362（PAH9）。这3个位点之间，PAH9与第3内含子中的STR位点（TCTA）n之间存在连锁不平衡，其他位点组合不存在连锁不平衡。联合第3内含子中的STR位点（TCTA）n和2个新的位点，可以对家系中突变基因标记进行95％N断，并成功地用于4例产前诊断中。结论选择性地应用PAH基因中的3个STR位点组合，可以95％地区分经典型苯丙酮尿症家系中父母的两个基因，从而准确地进行快速产前诊断。     

Implementing a Transition Program from Paediatric to Adult Services in Phenylketonuria: Results after Two Years of Follow-Up with an Adult Team

We aimed to report the implementation of a phenylketonuria (PKU) transition program and study the effects of follow-up with an adult team on metabolic control, adherence, and loss of follow-up. Fifty-five PKU patients were analysed in the study periods (SP): 2 years before (SP1) and after the beginning of adult care (SP2). Retrospective data on metabolic control and number of clinic appointments were collected for each SP, and protein intakes were analysed. In SP2, three patients (6%) were lost to follow-up. There was a small but statistically significant increase in median number of annual blood spots from SP1 to SP2: 11 (7–15) vs. 14 (7–20); p = 0.002. Mean ± SD of median blood Phe remained stable (525 ± 248 µmol/L vs. 552 ± 225 µmol/L; p = 0.100); median % of blood Phe < 480 µmol/L decreased (51 (4–96)% vs. 37 (5–85)%; p = 0.041) and median number of clinic appointments increased from SP1 to SP2: (5 (4–6) vs. 11 (8–13); p < 0.001). No significant differences were found regarding any parameter of protein intake. Our results suggest that the implementation of an adult service was successful as impact on metabolic control was limited and attendance remained high. Continuous dietetic care likely contributed to these results by keeping patients in follow-up and committed to treatment.     

内蒙古经典型苯丙酮尿症PAH基因外显子11突变的检测

目的：研究内蒙古地区经典型苯丙酮尿症（PKU）苯丙氨酸羟化酶（PAH）基因突变的特点和频率，以提高该地区PKU的基因诊断率。方法：应用PCR—SSCP-银染法和DNA直接测序的方法，对22例内蒙古地区PKU病人PAH基因外显子11进行了检测。站果：检出一种已知突变Y356X（TAC→TAA），突变频率为13．6％。结论：内蒙古地区PKU病人PAH基因外显子11的突变频率均高于我国的其它北方人群，也高于云南PKU病人的突变频率，这为内蒙古地区PKU病人PAH基因分析和产前诊断提供了科学依据。     

近14年四川省新生儿 PKU 及 CH 筛查情况分析

目的：分析四川省近14年间新生儿苯丙酮尿症（ PKU）和先天性甲状腺功能减低症（ CH）的筛查情况,为卫生行政部门提供决策依据。方法医务人员开展新生儿疾病筛查健康教育,经家长知情同意后对出生72小时后的新生儿进行血样标本采集、保存和递送;新筛中心及时验收血样标本,对合格标本进行PKU和CH筛查,对可疑或阳性结果进行复查,复查阳性者通知确诊。结果14年来四川省新生儿苯丙酮尿症和先天性甲状腺功能减低症筛查率和覆盖面逐年明显提高,2013年筛查率达到91．74％,市（州）筛查覆盖率达到100％,县（区）筛查覆盖率达到94．48％,采血单位覆盖率达到74．30％,年度筛查率、市（州）、县（区）、采血单位筛查覆盖率均有极显著性差异（χ2值分别为4530453．36、157．76、970．97、12314．65,均P＜0．01）。2000至2013年四川省新生儿PKU和CH筛查数为4348607,成都市新筛中心、自贡市新筛中心、南充市新筛中心、四川省新筛中心的年度筛查率均有极显著性差异（χ2值分别为879606．29、601375．16、379461．09、3030668．08,均P＜0．01）;确诊PKU138例,PKU发生率为1：31511,CH1711例,CH发生率为1：2542,各年度CH发病率有显著性差异（χ2＝37．59,P＜0．01）,各年度PKU发病率无显著性差异（χ2＝11．01,P＞0．05）。四川省新生儿苯丙酮尿症和先天性甲状腺功能减低症筛查仍有提升空间,筛查工作还有待进一步深入。结论14年来四川省新生儿苯丙酮尿症和先天性甲状腺功能减低症筛查工作取得明显成效,显示出明显的社会效益,需进一步加大相关工作力度,提高新生儿遗传代谢病筛查率和筛查质量。     

First structure of full-length mammalian phenylalanine hydroxylase reveals the architecture of an autoinhibited tetramer

Improved understanding of the relationship among structure, dynamics, and function for the enzyme phenylalanine hydroxylase (PAH) can lead to needed new therapies for phenylketonuria, the most common inborn error of amino acid metabolism. PAH is a multidomain homo-multimeric protein whose conformation and multimerization properties respond to allosteric activation by the substrate phenylalanine (Phe); the allosteric regulation is necessary to maintain Phe below neurotoxic levels. A recently introduced model for allosteric regulation of PAH involves major domain motions and architecturally distinct PAH tetramers [Jaffe EK, Stith L, Lawrence SH, Andrake M, Dunbrack RL, Jr (2013) Arch Biochem Biophys 530(2):73–82]. Herein, we present, to our knowledge, the first X-ray crystal structure for a full-length mammalian (rat) PAH in an autoinhibited conformation. Chromatographic isolation of a monodisperse tetrameric PAH, in the absence of Phe, facilitated determination of the 2.9 Å crystal structure. The structure of full-length PAH supersedes a composite homology model that had been used extensively to rationalize phenylketonuria genotype–phenotype relationships. Small-angle X-ray scattering (SAXS) confirms that this tetramer, which dominates in the absence of Phe, is different from a Phe-stabilized allosterically activated PAH tetramer. The lack of structural detail for activated PAH remains a barrier to complete understanding of phenylketonuria genotype–phenotype relationships. Nevertheless, the use of SAXS and X-ray crystallography together to inspect PAH structure provides, to our knowledge, the first complete view of the enzyme in a tetrameric form that was not possible with prior partial crystal structures, and facilitates interpretation of a wealth of biochemical and structural data that was hitherto impossible to evaluate.Mammalian phenylalanine hydroxylase (PAH) (EC 1.14.16.1) is a multidomain homo-multimeric protein whose dysfunction causes the most common inborn error in amino acid metabolism, phenylketonuria (PKU), and milder forms of hyperphenylalaninemia (OMIM 261600) (1). PAH catalyzes the hydroxylation of phenylalanine (Phe) to tyrosine, using nonheme iron and the cosubstrates tetrahydrobiopterin and molecular oxygen (2, 3). A detailed kinetic mechanism has recently been derived from elegant single-turnover studies (4). PAH activity must be carefully regulated, because although Phe is an essential amino acid, high Phe levels are neurotoxic. Thus, Phe allosterically activates PAH by binding to a regulatory domain. Phosphorylation at Ser16 potentiates the effects of Phe, with phosphorylated PAH achieving full activation at lower Phe concentrations than the unphosphorylated protein (5, 6). Allosteric activation by Phe is accompanied by a major conformational change, as evidenced by changes in protein fluorescence and proteolytic susceptibility, and by stabilization of a tetrameric conformer (3).There are >500 disease-associated missense variants of human PAH; the amino acid substitutions are distributed throughout the 452-residue protein and among all its domains (Fig. 1A) (7–9). Of those disease-associated variants that have been studied in vitro (e.g., ref. 10), some confound the allosteric response, and some are interpreted as structurally unstable. We also suggest that the activities of some disease-associated variants may be dysregulated by an altered equilibrium among conformers having different intrinsic levels of activity, arguing by analogy to the enzyme porphobilinogen synthase (PBGS) and its porphyria-associated variants (11). Consistent with this notion, we have recently established that PAH can assemble into architecturally distinct tetrameric conformers (12), and propose that these conformers differ in activity due to differences in active-site access. This idea has important implications for drug discovery, as it implies that small molecules could potentially modulate the conformational equilibrium of PAH, as has already been demonstrated for PBGS (e.g., ref. 13). Deciphering the relationship among PAH structure, dynamics, and function is a necessary first step in testing this hypothesis.Open in a separate windowFig. 1.The structure of PAH. (A) The annotated domain structure of mammalian PAH. (B) The 2.9 Å PAH crystal structure in orthogonal views, colored as in part A, subunit A is shown in ribbons; subunit B is as a Cα trace; subunit C is in sticks; and subunit D is in transparent spheres. In cyan, the subunits are labeled near the catalytic domain (Top); in red, they are labeled near the regulatory domain (Bottom). The dotted black circle illustrates the autoregulatory domain partially occluding the enzyme active site (iron, in orange sphere). (C) Comparison of the subunit structures of full-length PAH and those of the composite homology model; the subunit overlay aligns residues 144–410. The four subunits of the full-length PAH structure (the diagonal pairs of subunits are illustrated using either black or white) are aligned with the two subunits of 2PAH (cyan) and the one subunit of 1PHZ (orange). The catalytic domain is in spheres, the regulatory domain is in ribbons, and the multimerization domain is as a Cα trace. The arrow denotes where the ACT domain and one helix of 2PAH conflict.Numerous crystal structures are known for one- and two-domain constructs of mammalian PAH (14).

Table S1.

Mammalian PAH structures available in the PDB (August 2015)