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.     

Intellectual and Developmental Status in Children With Hyperphenylalaninemia and PKU Who Were Screened in a National Program

Background:

Hyperphenylalaninemia (HPA) and Phenylkeonuria (PKU) are metabolic errors caused by deficiency of phenylalanine hydroxylase enzyme, which results in increased level of phenylalanine. This increase is toxic to the growing brain.

Objectives:

The purpose of this study was to compare the intellectual and developmental status in HPA and PKU children with normal population in national screening program.

Patients and Methods:

In a historical cohort study, 41 PKU patients who had the inclusion criteria and 41 healthy children were evaluated. Wechsler preschool and primary scale of intelligence-3rd edition (WPPI-3) was used in order to assess the intellectual status of children 4 years and older and Ages and stages questionnaire (ASQ) was used to assess the developmental status of children 5 years and younger.

Results:

In intellectual test comparison, the two groups showed significant difference in Wechsler’s performance intelligence score and some performance subscales (P-value < 0.01). In comparison of developmental status, no significant difference was observed between the two groups (P-value > 0.05).

Conclusions:

Even with early diagnosis and treatment of PKU patients, these children show some deficiencies intellectually compared to normal children. This study emphasizes on necessity for screening intellectual and developmental status of PKU patients so that effective medical or educational measures can taken in case of deficiencies.     

Early replacement therapy in a first Japanese case with autosomal recessive guanosine triphosphate cyclohydrolase I deficiency with a novel point mutation

Autosomal recessive guanosine triphosphate cyclohydrolase I (GTPCH) deficiency is an inborn error of tetrahydrobiopterin (BH4) synthesis from GTP. GTPCH deficiency causes severe reduction of BH4, resulting in hyperphenylalaninemia (HPA) and decreased dopamine and serotonin synthesis. Without treatment, a patient with GTPCH deficiency develops complex neurological dysfunctions, including dystonia and developmental delays. The first Japanese patient with GTPCH deficiency was discovered by HPA during asymptomatic newborn screening. The phenylalanine level at the age of 5 days was 1273 μmol/L (cutoff value, 180.0 μmol/L). The high serum phenylalanine level was decreased to normal after adequate BH4 oral supplementation. Serum and urinary pteridine examination revealed very low levels of neopterin and biopterin. Sequence analysis of GCH1 revealed compound heterozygous point mutations, including a novel point mutation (p.R235W). Replacement therapy with BH4 and L-dopa/carbidopa were started at the age of 1 month, and 5-hydroxytryptophan (5-HTP) was started at the age of 5 months. At 10 months of age, the patient showed slight dystonia but no obvious developmental delay. Cerebrospinal fluid should be examined to determine the appropriate dosage of supplement drugs. In conclusion, it is important to control the serum phenylalanine level and perform early replacement of neurotransmitters to prevent neurological dysfunction.     

红细胞二氢蝶啶还原酶活性测定方法的建立和应用

目的建立红细胞二氢蝶啶还原酶(DHPR)活性测定方法,对高苯丙氨酸血症(HPA)者进行DHPR缺乏型四氢生物蝶呤(BH4)缺乏症筛查。方法采用UV-2450型双光束分光光度仪、1 mmol/L细胞色素C及20 mmol/L 6-甲基四氢蝶呤等试剂测定外周干滤纸血片中DHPR活性。结果DHPR活性与年龄无关,该实验室儿童DHPR活性参考值为(2.2±0.7)nmol/(m in.5 mmd isc)[(1.02~3.35)nmol/(m in.5 mmd isc)];实验批内变异系数(CV)为9.1%,批间CV为11.5%,实验最好在37℃恒温下进行;30例HPA患儿DHPR活性测定结果为(2.4±0.8)nmol/(m in.5 mmd isc),未发现DHPR缺乏者。结论干滤纸血片中红细胞DHPR活性测定是DHPR缺乏症有效、可靠且易行的诊断方法。     

Tetrahydrobiopterin responsiveness in patients with phenylketonuria

OBJECTIVES: To investigate the BH4 response in a group of patients with phenylketonuria (PKU) in order to offer this alternative treatment to the responsive patients. DESIGN AND METHODS: The 24-h-long Phe/BH4 loading test was performed on 64 PKU patients requiring dietary treatment. RESULTS: All patients with mild-PKU and 75% of patients with moderate-PKU were BH4 responsive, while only 11% of classic-PKU patients showed good/partial response (P < 0.0001). The percentages of Phe decrease after the BH4 loading test were significantly different in the three PKU phenotypes (mild PKU: 67.9 +/- 18.7; moderate PKU: 37.4 +/- 16.8; and classical PKU: 21.9 +/- 13.7; ANOVA with Bonferroni correction: P < 0.0001). We report four mutations (P147S, D222G, P275S, and P362T) not previously associated with BH4 responsiveness, all of them combined with mutations with zero predicted residual activity. CONCLUSION: Both the percentage of Phe decrease and the Phe value achieved 24 h after BH4 loading are valuable data in predicting a response. We report four mutations not previously associated with BH4 responsiveness.     

In vivo regulation of phenylalanine hydroxylase in the genetic mutant hph-1 mouse model

The hph-1 mouse has low liver activity of GTP cyclohydrolase 1, the rate limiting enzyme in the biosynthesis of tetrahydrobiopterin (BH₄). BH₄ is the cofactor for phenylalanine hydroxylase (PAH) and in the early stages of life the hph-1 mouse is hyperphenylalaninemic. At approximately 15 days after birth the blood phenylalanine levels normalize. During this period the animals provide an in vivo model which can be used to study the regulatory effects of phenylalanine on PAH, and for related pediatric metabolic disease in humans; from birth to youth. We therefore, examined; liver PAH activity using BH₄ and 6-methyltetrahydropterin (6MPH₄) as cofactor; PAH total enzyme concentration by Western blotting using the PH8 antibody, and PAH state of phosphorylation using the PH7 antibody from 4 to 18 days after birth. The findings were compared to the wild type animals that are not hyperphenylalaninemic during this period. PAH (6MPH₄) activity and total protein (PH8 antibody) rose steadily in the hph-1 mice. In control mice, both activity and total protein fluctuated. The degree of phosphorylation of PAH in the mutants and the state of activation (as measured by the 6MPH₄/BH₄ activity ratio) increased as phenylalanine levels rose, and decreased when they fell. Similar patterns were not seen in the control animals. These studies provide in vivo evidence that phenylalanine concentration regulates the activity of PAH in the hph-1 mouse and that this acts via a mechanism that includes phosphorylation of the PAH molecule. The kinetic values (K_m and V_max) for mouse PAH are also reported.     

Induced PKU in rats: effects of age and melatonin treatment

Newborn rats injected on Days 1-8 of life with L-phenylalanine (2 g/kg) and p-chlorophenylalanine (80 mg/kg) displayed biochemical symptoms analogous to human phenylketonuria (PKU) and maze learning impairments. The behavioral effects were less evident in rats treated on Days 9-16 or 7-24. None of the symptoms observed were alleviated by simultaneous administration of melatonin (10 mg/kg/day).     

Incidence of Neonatal Hyperphenylalaninemia in Fars Province,South Iran

Objective

Phenylalanine hydroxylase or its cofactor, tetrahydrobiopterin (BH₄), deficiency causes accumulation of phenylalanine in body fluids and central nervous system. Considering the fact that hyperphenylalaninemia is a preventable cause of mental retardation in infants, the objective of this study was to determine the incidence of congenital hyperphenylalaninemia in Fars province, south of Iran.

Methods

In a period of one year from November 2007 to November 2008 blood samples were withdrawn from all newborns born in Fars province for measurement of serum phenylalanine. The samples with a serum level of≥ 2 mg/dl were referred to pediatric endocrine clinic for confirmation and determination of the type of hyperphenylalaninemia by quantitive serum phenylalanine measurements by using High-Pressure liquid chromatography (HPLC) method.

Findings

Nine out of 76966 newborns had a serum phenylalanine level≥2mg/dl, of which 8 cases were confirmed by HPLC. The incidence of the disease was 1:10000. The incidence of mild hyperphenylalaninemia and phenylketonuria (PKU) among the patients was 62.5% and 37.5% respectively and the incidence of BH₄ deficiency was 1/76966.

Conclusion

These findings indicate a high incidence of hyperphenylalaninemia, in the newborns from Fars province. The high incidence makes a comprehensive screening program for management of the disease necessary.     

A defective splice site at the phenylalanine hydroxylase gene in phenylketonuria and benign hyperphenylalaninemia among Palestinian Arabs.

Phenylketonuria (PKU) and benign hyperphenylalaninemia (HPA) result from different combinations of mutations at the locus for phenylalanine hydroxylase (PAH). While some of these mutations show widespread ethnic distribution, others are unique to specific communities. We report here the first point mutation common among Palestinian Arabs. The mutation (IVS2nt1) involves a dinucleotide substitution (Gg-->Aa) at the donor splice site of intron 2 of the PAH gene and abolishes a recognition site of the restriction enzyme MnlI. IVS2nt1 is associated with two PAH polymorphic haplotypes, 7 and 42. Homozygotes for this mutation are affected with severe, classical PKU. Compound heterozygotes carrying the IVS2nt1 allele and one of several other yet unknown mutations show different degrees of benign HPA.     

高苯丙氨酸血症的抽搐机制研究

目的四氢生物喋呤缺乏症和苯丙酮尿症均可导致继发性癫痫,本研究拟探讨两类患者的临床与实验室特点。方法将两组患者出现癫痫的年龄、发作形式、脑电图特点及治疗预后进行比较。结果在391例晚治的高苯丙氨酸血症患者中,共有98例苯丙酮尿症和12例四氢生物喋呤缺乏症患者合并癫痫。98名苯丙酮尿症患者出现癫痫发作的年龄是10.7±4.6(4.5~27.1)个月,表现为多种形式,其中55例(56.1%)表现为婴儿痉挛症。经丙戊酸钠和其他抗癫痫药物治疗后,癫痫较难控制,经低苯丙氨酸饮食治疗后临床发作及脑电图均有所减轻。12例四氢生物喋呤缺乏症患儿出现癫痫的年龄为5.1±1.9(2.7~11.0)个月,主要表现为肢体铅管样扭转,哈气样症状。其中10例患者进行了脑电图检查,3例有轻度的痫样放电,7例脑电图正常。治疗后随访脑电图无特异性变化。在服用美多巴后,发作立即得到控制。结论四氢生物喋呤缺乏症和苯丙酮尿症导致癫痫的机制不同,两组患者发作开始年龄、形式、脑电图表现差异显著,治疗方法及预后完全不同。