Genetic background of hyperphenylalaninemia in Nagasaki,Japan

Phenylketonuria (PKU) and related hyperphenylalaninemia (HPA) are caused by a deficiency in hepatic phenylalanine hydroxylase (PAH). The incidence of PKU in Nagasaki prefecture is higher than that in all parts of Japan (1/15 894 vs 1/120 000). To investigate the genetic background of patients with HPA in Nagasaki prefecture, mutation analysis was done in 14 patients with PKU or mild HPA. Homozygous or compound heterozygous PAH mutations were identified in all the patients. The spectrum of PAH mutations in the cohort was broad and similar to those in all parts of Japan and East Asian countries. R53H is the most common mutation in patients with mild HPA. The present results provide further support for genotype–phenotype correlations in patients with HPA. The high incidence of PKU in Nagasaki, the westernmost part of Japan, might be due to migration of people with PAH mutations from China and Korea, and geographic factors.     

四氢生物蝶呤反应性苯丙氨酸羟化酶缺乏症的临床与基因研究

目的 探讨四氢生物蝶呤（tetrahydrobiopterin,BH4）反应性苯丙氨酸羟化酶（phenylalanine hydroxylase,PAH）缺乏症临床表型和基因型的关系。方法 38例高苯丙氨酸血症（hyperphenylalaninemia,HPA）患儿均进行口服BH。负荷试验（20ms／kg）或Phe-BH。联合负荷试验,同时进行尿蝶呤谱分析、红细胞二氢蝶啶还原酶（dihyaropteridine reductase,DHPR）测定。对7例BH4反应性PAH缺乏症患儿采用聚合酶链反应（PCR）和单链构象多态性（single strand conformation polymorphism,SSCP）分析对PAH外显子进行突变筛检,并结合DNA直接测序方法进行突变分析。结果 确诊10例BH4反应性PAH缺乏症患儿,男6例,女4例;平均年龄7．8个月;生化代谢表型均为轻度或中度HPA。7例BH4反应性PAH缺乏症患儿PAH基因型分别为S70del／-、R241C／R243Q、S70del／A389G、Y166X／-、R11lX/-、EX6-96A〉G／R241C和IVS4-1G〉A／R241C。A389G是新发现的突变基因型。结论 BH4反应性PAH缺乏症多表现为轻、中度HPA生化代谢表型,R241C是BH4反应性相关突变基因型中较常见的一种类型。推测S70del可能是一种BH4反应性相关突变类型.     

Relation between genotype and phenotype in Swedish phenylketonuria and hyperphenylalaninemia patients

Phenylketonuria (PKU) and hyperphenylalaninemia (HPA) are caused mostly by an inherited (autosomal recessive) deficiency in hepatic phenylalanine hydroxylase (PAH) activity. More than 50 PAH mutations have ben reported. The goal of the present study was to examine the molecular basis for the clinical heterogeneity of Swedish PKU and HPA patients. Mutations were identified through allele-specific oligonucleotide hybridization or DNA sequencing on 128 of the 176 mutant alleles (73%). Three mutations (R408W, Y414C and IVS12) together accounted for 56% of all mutant alleles and ten relatively infrequent mutations were found on another 17% of all mutant alleles. Patients from 50 of the 88 families (57%) had identified mutations in both PAH genes and allowed use to compare the clinical effects of different combinations of PAH mutations. The in vitro activity of all of these mutations, including the newly identified G272X and L364, have been tested in a eukaryotic expression system. There was a strong relationship between the average in vitro PAH activity of the two mutant enzymes and both the phenylalanine tolerance and the neonatal pretreatment serum phenylalanine concentration. This confirms previous observations in Danish and German PKU patients that disease phenotype is a consequence of the nature of the mutations at the PAH locus and not significantly influenced by other loci. The sample population in the previous study did not, however, include mild HPA patients, and the observed correlation is thus restricted to severe and moderate mutant alleles. Since a comparatively high proportion of the Swedish patients were mildly affected, we have provided additional evidence that this correlation is valid throughout a continuous spectrum of clinical varieties. PAH genotyping could therefore help predict prognosis of a recently diagnosed PKU or HPA child.     

Atypical cases of phenylketonuria

Conclusion Neonatal HPA can be caused by deficiency of PAH or of its cofactor. At present, conventional methods are not able to delineate the molecular basis of the mutations in PKU patients. DNA analysis might in future visualize the different genotypes, but might not solve the problem of therapeutic decision.All infants with HPA should be screened for THB deficiency. Diagnostic tools are now available for the recognition of these variants among hyperphenylalaninemic infants. The most important question-which infants can achieve normal development if treated early-remains tobe answered. Efforts have to be directed toward better characterization of individual residual capacity to synthesize THB and toward and definition of protocols for the follow-up of neurotransmitter replacement therapy.Abbreviations PKU phenylketonuria - HPA hyperphenylalaninemia - PAH phenylalanine hydroxylase - DHPR dihydropteridine reductase - BS biopterin synthetase - THB tetrahydrobiopterin - GTP guanosine triphosphate - GTP-ch GTP-cyclohydrolase - N/B ratio neopterin/biopterin ratio     

四氢生物蝶呤反应性苯丙氨酸羟化酶缺乏症

目的：四氢生物蝶呤(BH4)可以使BH4缺乏症病人的血液苯丙氨酸水平正常化,但是对苯丙酮酸尿症(PKU)病人无效。最近在新生儿PKU筛查中发现了对BH4有反应的轻度PKU患者。本研究将探讨BH4和苯丙氨酸羟化酶(PAH)基因突变在对BH4有反应的轻度PKU和轻度高苯丙酸血症(HPA)患者中的作用。方法：对经新生儿PKU筛查中发现的生物蝶呤代谢正常的轻度HPA患者,进行单次(10mg/kg)、4次、1周[20 mg/(kg·d)]的BH4口服负荷试验及长期BH4治疗,评估其对BH4口服负荷试验的反应性。结果：在单剂量BH4口服负荷试验中,典型PKU患者的血苯丙氨酸水平没有降低。在单剂量BH4口服负荷试验中血苯丙氨酸水平下降超过20%的患者,在4次BH4口服负荷试验中下降亦超过20%。1周BH4负荷试验确认在单剂量和4次BH4负荷试验中表现出弱反应性的病人对BH4有反应。许多患轻度PKU和轻度HPA且有R241C基因位点的病人,都对BH4治疗有反应。在无BH4反应性的典型PKU病人中未发现R241C、P407S和A373T基因突变。结论：1周BH4负荷试验用于诊断BH4反应性PAH缺乏症最为有效。等位基因R241C、P407S和A373T与轻度HPA和轻度PKU病人具有H4反应性有关。BH4治疗是针对轻度HPA和轻度PKU的一种新颖、有效的药物治疗,有望代替限制苯丙氨酸饮食的方法。     

青岛市苯丙氨酸羟化酶缺乏症患儿基因突变分析

目的探讨青岛市苯丙氨酸羟化酶(phenylalanine hydroxylase,PAH)缺乏症患儿的基因突变特点,为青岛市PAH缺乏症的产前诊断、治疗提供科学参考依据。方法对经青岛市新生儿疾病筛查确诊的44例PAH缺乏症患儿,应用第二代高通量测序及多重连接酶探针依赖扩增(multi-ligase probe dependent amplification,MLPA)技术进行基因分析,检测患儿基因突变位点,应用Sanger测序对其父母的PAH基因相应突变位点进行检测并验证。根据患儿血苯丙氨酸浓度,分为经典型苯丙酮尿症、轻度苯丙酮尿症和轻度高苯丙氨酸血症。结果①44例PAH缺乏症患儿PAH基因中均检测到2个突变位点,其中2例为纯合突变,纯合突变的频率为4.6%,所有突变在患儿父母相应突变位点处均能检测到。②44例PAH缺乏症患儿共检测到突变36种,其中c.728G>A突变频率最高(15.9%,14/88),其次是c.1068C>A(10.2%,9/88),再次为c.158G>A(9.1%,8/88)。③21例经典型苯丙酮尿症患儿PAH基因突变19种,其中c.1068C>A突变频率最高(21.4%,9/42),其次是c.728G>A(19.0%,8/42)。10例轻度苯丙酮尿症患儿PAH基因突变14种,其中c.721C>T/722delG突变频率最高(15.0%,3/20),其次为c.1197A>T、c.1301C>A、c.721C>T、c.728G>A(均为10.0%,2/20)。13例轻度高苯丙氨酸血症患儿PAH基因突变17种,其中c.158G>A突变频率最高(26.9%,7/26),其次为c.728G>A(15.4%,4/26)。结论青岛市PAH缺乏症患儿PAH基因突变以复合杂合突变为主,具有明显热点突变(c.728G>A、c.1068C>A、c.158G>A),经典型苯丙酮尿症患儿以c.1068C>A、c.728G>A为主,轻度苯丙酮尿症患儿以c.721C>T/722delG为主,轻度高苯丙氨酸血症患儿以c.158G>A为主。本研究明确了青岛市PAH缺乏症患儿基因的突变类型与特点,为深入开展PAH缺乏症的诊断以及进一步的基因治疗奠定了基础。     

In vivo studies of phenylalanine hydroxylase by phenylalanine breath test: diagnosis of tetrahydrobiopterin-responsive phenylalanine hydroxylase deficiency

Tetrahydrobiopterin (BH4)-responsive phenylalanine hydroxylase (PAH) deficiency is characterized by reduction of blood phenylalanine level after a BH4-loading test. Most cases of BH4-responsive PAH deficiency include mild phenylketonuria (PKU) or mild hyperphenylalaninemia (HPA), but not all patients with mild PKU respond to BH4. We performed the phenylalanine breath test as reliable method to determine the BH4 responsiveness. Phenylalanine breath test quantitatively measures the conversion of L-[1-13C] phenylalanine to 13CO2 and is a noninvasive and rapid test. Twenty Japanese patients with HPA were examined with a dose of 10 mg/kg of 13C-phenylalanine with or without a dose of 10 mg . kg(-1) . d(-1) of BH4 for 3 d. The phenylalanine breath test [cumulative recovery rate (CRR)] could distinguish control subjects (15.4 +/- 1.5%); heterozygotes (10.3 +/- 1.0%); and mild HPA (2.74%), mild PKU (1.13 +/- 0.14%), and classical PKU patients (0.29 +/- 0.14%). The genotypes in mild PKU cases were compound heterozygotes with mild (L52S, R241C, R408Q) and severe mutations, whereas a mild HPA case was homozygote of R241C. CRR correlated inversely with pretreatment phenylalanine levels, indicating the gene dosage effects on PKU. BH4 loading increased CRR from 1.13 +/- 0.14 to 2.95 +/- 1.14% (2.6-fold) in mild PKU and from 2.74 to 7.22% (2.6-fold) in mild HPA. A CRR of 5 to 6% reflected maintenance of appropriate serum phenylalanine level. The phenylalanine breath test is useful for the diagnosis of BH4-responsive PAH deficiency and determination of the optimal dosage of BH4 without increasing blood phenylalanine level.     

Science, medicine and phenylketonuria

Science addresses ignorance; medicine uses facts. The scientific approach to phenylketonuria (PKU) led to the discovery of its causes, both ultimate (allelic heterogeneity at the PAH locus) and proximate (dietary phenylalanine), the proximal phenotype (phenylalanine hydroxylase deficiency), the associated metabolic phenotype and the major distal phenotype (impaired cognitive development and neuropsychological function) for which the pathogenesis is still being investigated. By applying knowledge through newborn screening, early diagnosis and treatment, the brain disease of PKU has been greatly ameliorated. The population approach, which converted incidence into cases, revealed genetic heterogeneity in hyperphenylalaninemia involving four other loci, controlling cofactor (BH₄) synthesis and recycling, and non-random geographic distribution of mutant PAH alleles of which more than 170 were known in April 1994. Various mechanisms including founder effect, genetic drift, hypermutability and selection (perhaps) explain the polymorphic aggregate frequency (∼ 0.01) and spectrum of PKU mutations in human populations.     

Automated sequencing detects all mutations in Northern Irish patients with phenylketonuria and mild hyperphenylalaninaemia

In the first phase of the Northern Ireland PKU Study, we used automated sequencing to identify the spectrum of mutations in a random group of 32 unrelated phenylketonuria (PKU) families. We also investigated 7 Northern Irish patients with mild hyperphenylalaninaemia not requiring dietary intervention (MHP, previously referred to as non-PKU HPA). Disease-causing mutations were identified on all 78 investigated chromosomes. We found 23 different mutations, including 20 missense, 1 nonsense and 2 splice site mutations. All mutations were located within exons or at intronexon boundaries of the phenylalanine hydroxylase gene. Seven mutations occurred at CpG sites, confirming these sites as mutation hot-spots in PKU. Mutations R408W and I65T are the two commonest PKU mutations in the Northern Irish population. Two mutations (T380M and V245A) can be characterized as MHP mutations; they are quasi dominant markers for MHP since they cause mild hyperphenylalaninaemia even when occurring in conjunction with the most severe PKU mutations. The results have proven valuable for the development of a routine PKU mutation analysis system in Northern Ireland.     

Long-term treatment and diagnosis of tetrahydrobiopterin-responsive hyperphenylalaninemia with a mutant phenylalanine hydroxylase gene

A novel therapeutic strategy for phenylketonuria (PKU) has been initiated in Japan. A total of 12 patients who met the criteria for tetrahydrobiopterin (BH(4))-responsive hyperphenylalaninemia (HPA) with a mutant phenylalanine hydroxylase (PAH) (EC 1.14.16.1) gene were recruited at 12 medical centers in Japan between June 1995 and July 2001. Therapeutic efficacy of BH(4) was evaluated in single-dose, four-dose, and 1-wk BH(4) loading tests followed by long-term BH(4) treatment, and also examined in relation to the PAH gene mutations. The endpoints were determined as the percentage decline in serum phenylalanine from initial values after single-dose (>20%), four-dose (>30%), and 1-wk BH(4) (>50%) loading tests. Patients with mild PKU exhibiting decreases in blood phenylalanine concentrations of >20% in the single-dose test also demonstrated decreases of >30% in the four-dose test. The 1-wk test elicited BH(4) responsiveness even in patients with poor responses in the shorter tests. Patients with mild HPA, many of whom carry the R241C allele, responded to BH(4) administration. No clear correlation was noted between the degree of decrease in serum phenylalanine concentrations in the single- or four-dose tests and specific PAH mutations. The 1-wk test (20 mg/kg of BH(4) per day) is the most sensitive test for the diagnosis of BH(4)-responsive PAH deficiency. Responsiveness apparently depends on mutations in the PAH gene causing mild PKU, such as R241C. BH(4) proved to be an effective therapy that may be able to replace or liberalize the phenylalanine-restricted diets for a considerable number of patients with mild PKU.     

PKU and NON-PKU Hyperphenylalaninemia: Differentiation, Indication for Therapy and Therapeutic Results

The differential diagnosis of phenylalanine hydroxylase deficiency (PAHD) by biochemical methods is difficult. Using standardized oral protein loading or the intravenous deuterated phenylalanine (phe) load in 46 patients with PAHD, three groups could be distinguished: 1) Phenylketonuria (PKU) with plasma phe levels over 20 mg% under the protein load and with residual activities of less than 1% of normal; 2) mild PKU with plasma phe of 10–20 mg% and residual enzyme activities of 1–3%; 3) Non-PKU hyperphenylalaninemia with plasma phe levels of less than 10 mg% and residual enzyme activities of more than 3%. Psychomotor development in 32 untreated patients with PAHD showed that there is a high risk of brain damage for all patients with in vivo residual activities of less than 3% of normal. Restriction fragment length polymorphism (RFLP) haplotypes at the phenylalanine hydroxylase (PAH) locus in 60 German patients with PAHD showed that 90% of the mutant alleles are confined to four distinct haplotypes. Using an oligonucleotide probe for the splicing mutation associated with mutant haplotype 3 a close association between the mutation and the haplotype 3 has been observed. There is also an association between haplotypes 2 and 3 and PKU patients with residual enzyme activities of less than 1%. However, in only 37% of our patients with PAHD could a direct diagnosis of the mutations in the PAH gene be made. More knowledge of other mutations in the PAH gene is necessary to differentiate patients with PAHD on the DNA level.     

北京地区苯丙酮尿症基因突变构成及基因型与表型相关分析

目的 明确北京地区苯丙酮尿症(phenylketonuria,PKU)患儿苯丙氨酸羟化酶基因(phylalanine hydroxylase gene,PAH)突变图谱及其突变基因的微单体型(STR/VNTR)构成,探讨突变基因型与生化代谢表型的相关关系.方法 应用PCR/SSCP、序列分析和变性凝胶电泳等技术,对50例北京地区PKU患儿及其父母,进行PAH基因的全部外显子及两侧的内含子序列和STR与VNTR多态性分布的分析.依据由基因型预测生化代谢表型的方法进行基因型与生化代谢表型的相关关系分析.结果 (1)共检测到34种PAH突变基因,总的检出率为95%;较为常见的突变有R243Q(20%)、EX6-96A＞G(11%)、Y356X(9%)和V399V(7%),其次是R111x(5%)、R413P(5%)、R252Q(3%)和A434D(3%).(2)北京地区PKU患儿的STR杂合度较高,共检测出8种等位基因,以240 bp(34%)和244 bp(44%)最为常见;而VNTR的杂合度较低,只检测到3种等位基因,以VNTR3(83%)最为常见.(3)由基因型预测的生化代谢表型与患儿实际的生化代谢表型之间一致率为81.5%,在经典型PKU中一致率达到87.5%.结论 (1)北京地区共有34种PAH基因突变,检出率为95%,以R243Q、EX6-69A＞G、Y356X和V399V突变为常见突变.(2)PAH突变基因的微单位(STR/VNTR)构成以240/3和244/3最为常见.(3)PKU患儿基因型与生化代谢表型之间存在较好的相关关系,一致率达到80%以上.     

Follow-up study of 16 years neonatal screening for inborn errors of metabolism in West Germany

Capillary blood samples from almost one million neonates from Baden-Württemberg were investigated for inborn errors of metabolism between 1969 and 1984 in our screening centre. Besides 7 patients with maple syrup urine disease (MSUD), 3 with homocystinuria and 18 with galactosaemia, a follow-up of the positive screening results confirmed 94 patients with phenylketonuria (PKU) and 76 with non-PKU hyperphenylalaninaemia (non-PKU HPA). The incidence of PKU is 1: 10 000, and that of HPA in the wider sense (PKU and non-PKU HPA) as obtained by newborn screening before further classification at 6 months 1: 5532.For West Germany as a whole, the number of newly discovered cases with persistent hyperphenylalaninaemia was 1480 in the same period. The subdivision into PKU and non-PKU HPA is not yet possible from this figure. It is strongly suggested that the abnormal results of newborn screening for phenylalanine be designated as hyperphenylalaninaemia (in the wider sense) and that the terms PKU or non-PKU HPA be used only after further differentiation as carried out by us at the age of 6 months.Abbreviations MSUD maple syrup urine disease - PKU phenylketonuria - non-PKU HPA non-PKU hyperphenylalaninaemia     

四氢生物蝶呤负荷试验诊断四氢生物蝶呤反应性苯丙氨酸羟化酶缺乏症的临床研究

目的探讨四氢生物蝶呤(BH4)反应性苯丙氨酸羟化酶(PAH)缺乏症的临床诊断方法,进一步了解其临床特征,为该型患儿应用BH4药物治疗提供科学依据。方法73例高苯丙氨酸血症(HPA)患儿,男47例,女26例,平均年龄1.93个月。所有患儿都进行口服BH4负荷试验,同时进行尿蝶呤谱分析、红细胞二氢蝶啶还原酶测定。对其中血苯丙氨酸(Phe)浓度<600μmol/L者给予口服Phe BH4联合负荷试验,对部分BH4反应性PAH缺乏症患儿,在普食条件下给予BH4片剂(10～20mg/kg)替代治疗6～7天,观察其疗效。结果(1)在BH4负荷试验中,不同类型HPA患儿的血Phe浓度表现出特征性的曲线改变,22例诊断为经典型苯丙酮尿症(PKU),39例中度PKU,12例四氢生物蝶呤缺乏症;(2)在中度PKU患儿中发现22例(56.4%)对BH4有反应;(3)6例BH4反应性PAH缺乏症患儿以BH410mg/kg治疗6～7天,其中4例血Phe浓度能控制到正常或接近正常治疗水平,另2例BH4需增加到20mg/kg使Phe浓度显著下降。结论在BH4负荷试验中,部分因苯丙氨酸羟化酶缺乏引起的中轻度PKU患儿对BH4有反应性,给予这些患儿BH4治疗可部分或全部替代低苯丙氨酸饮食治疗,拓宽了PKU的治疗方法,有助于提高患儿的生活质量。     

上海地区遗传代谢病的新生儿筛查(英文)

Objectives Inborn errors of metabolism (IEM) has a diverse spectrum and different incidence in different countries, the early diagnosis at presymptomatic stage is imperative to benefic patient from sequelae. Phenylke-tonuria (PKU) / hyperphenylalaninemia (HPA) is the most common metabolism disorder in Shanghai as well as in other regions. The study is to further clarify the incidence of inborn errors of metabolism among newborn in Shanghai. Methods The dried blood spot specimens were collected from near 90 ...     

In vivo assessment of mutations in the phenylalanine hydroxylase gene by phenylalanine loading: Characterization of seven common mutations

Abstract Mutations in the gene encoding phenylalanine hydroxylase (PAH) cause persistent hyperphenyl-alaninaemia. To date, more than 200 point mutations and microdeletions have been characterized. Each mutation has a particular quantitative effect on enzyme activity and recessive expression of different mutant alleles results in a marked interindividual heterogeneity of metabolic and clinical phenotypes. In this paper we demonstrate how a simple clinical test can be used to evaluate the correlation between mutation genotype and phenylalanine metabolism. In hyperphenylalaninaemic patients with known PAH mutation genotype, we have investigated phenylalanine turnover in vivo by measuring the ability to eliminate a test dose ofl-phenyl-alanine. All patients could be considered functionally hemizygous for one of their mutant alleles by carrying on the other allele a mutation that is known to completely abolish PAH activity and encode a peptide with no immunoreactivity. Seven mutations (R408W, IVS-12nt1, R261Q, G46S, Y414C, A104D, and D415N) were characterized by oral phenylalanine loading, each mutation being represented by at least three patients. The elimination profile determined for a 3-day period provides a measure to compare residual activity of the mutant proteins and to assign each mutation to a particular metabolic phenotype. The established relation between genotype and phenotype may enable prediction of the severity of the disease by genotype determination in the newborn period. This will aid in the management of hyperphenylalaninaemia and may improve prognosis.Conclusion The possibility of predicting the residual enzyme activity by DNA analysis performed already in the newborn period allows the prompt implementation of a diet that is adjusted to the degree of PAH deficiency. This may improve management and prognosis of hyperphenylalaninaemia.     

The PKU mouse project: its history, potential and implications

To produce genetic-based animal models for the human disease phenylketonuria (PKU), we treated mice with the powerful germline mutagen ethylnitrosourea and screened the progeny of these animals for the symptom hyperphenylalaninemia (HPH). Six independent mutant strains have been produced to date that exhibit heritable HPH. The first mutation isolated was found to cause a reduced level of GTP-cyclohydrolase I activity and, as such, yields a model for tetrahydrobiopterin-dependent HPH. The next two mutations have yet to be fully characterized but cause syndromes that appear distinct from any PKU or HPH syndromes yet reported for humans and they are allelic. Next we isolated a mutation that caused a marked reduction in hepatic phenylalanine hydroxylase activity levels. The enzyme deficiency was not sufficient to cause a PKU syndrome but instead produced a mild HPH syndrome. This strain played an instrumental role, however, in the identification of two additional mutant strains that appear to model human PKU very accurately in the laboratory mouse. These latter strains have levels of HPH very similar to human PKU patients, exhibit a phenylalanine-dependent hypopigmentation, and have reproductive difficulties that resemble human maternal PKU.     

Assessment of tetrahydrobiopterin responsiveness in Turkish hyperphenylalaninemic patients

Tetrahydrobiopterin (BH4) therapy is the latest alternative approach in phenylalanine hydroxylase (PAH) deficiency, and is suggested for a number of hyperphenylalaninemic (HPA) patients with certain mutations. In our unit, therapeutic efficacy of BH4 was evaluated in 20 HPA patients (4 mild HPA, 9 mild phenylketonuria-PKU, 7 moderate PKU) by a single oral dose of BH4. Overall, 60% of the patients responded (45% favorably, 15% partially). All of the mild HPA patients and 55% of mild PKU patients responded to BH4 favorably and an additional 11% of mild PKU patients responded partially. Of 7 moderate PKU patients, 2 responded partially (28%). The genotypes of the patients who responded to BH4 favorably were: DelF39/-, L48S/L48S, R261Q/- (4 patients), A300S/IVS2nt5g > c, A300S/-, E390G/E390G. The genotypes of the patients who exhibited a partial response were: L48S/L48S, R261Q/ R261Q, IVS10nt546/-. We concluded that since there are too many mutations and many patients are compound heterozygote, it is difficult to predict BH4 responsiveness based solely on genotype, especially for the mutations which show inconsistent phenotypes. The best way to identify the patients who are more likely to benefit from BH4 administration is performing BH4 loading test. Long-term BH4 loading test should be performed in classical and moderate PKU patients to confirm that they are not responsive to BH4.     

Follow-up study of a nation-wide neonatal metabolic screening program in Japan

A nationwide neonatal sreening program for phenylketonuria (PKU), maple syrup urine disease (MSUD), homocystinuria, histidinemia and galactosemia was started in Japan in 1977. The total number of infants screened had reached 6,311,754 by March, 1982. A follow-up study revealed the incidence of the disease in Japan: 1/108,823 for PKU; 1/450,840 for hyperphenylalaninemia (HPA); 1/1,577,939 for biopterin deficiency; 1/525,980 for MSUD; 1/1,051,959 for homocystinuria; 1/8,371 for histidinemia, and 1/788,969 for galactosemia type 1. The incidences of PKU, HPA, homocystinuria, and galactosemia (type 1) were found to be markedly low in Japan as compared with those in Caucasian countries. There was no great difference in the incidence of MSUD between both. On the other hand, the incidence of histidinemia was higher in Japan.It was found that most of the patients with PKU, HPA, MSUD, homocystinuria, or galactosemia are developing normally due to the early initiation of dietary treatment. These results clearly indicate that the neonatal mass screening program plays a great role in preventing the occurrence of handicapped children.