Diagnosis and treatment of hereditary tyrosinemia in Japan

Hereditary tyrosinemia is an autosomal recessive inherited disease that manifests as three types (types I–III). We conducted a nationwide survey of this disease in Japan, and here review the results in relation to prevalence, clinical characteristics, and treatment and diagnosis. A definitive diagnosis of tyrosinemia type I is difficult to obtain based only on blood tyrosine level. Detection of succinylacetone using dried blood spots or urinary organic acid analysis, however, is useful for diagnosis. In tyrosinemia type I, dietary therapy and nitisinone (Orfandin®) are effective. Prognosis is greatly affected by the complications of liver cancer and hypophosphatemic rickets; even patients that are treated early with nitisinone may develop liver cancer. Long‐term survival can be expected in type I if nitisinone therapy is effective. Prognosis in types II and III is relatively good.     

Response of metastatic recurrent neuroblastoma to nitisinone: a modulator of tyrosine metabolism

Nitisinone blocks the tyrosine pathway and may be effective in treating neuroblastoma. A 33-month-old male with heavily treated metastatic, recurrent, N-MYC amplified neuroblastoma received nitsinone (0.8 mg/kg/day escalated to 5.0 mg/kg/day). Dramatic tumor regression and resolution of pain without toxicity were observed. At 10 weeks, the tumor progressed. Nitisinone, low dose cyclophosphamide and doxorubicin subsequently produced a very good partial response. At 18 months the disease progressed. The child succumbed 21 months after starting nitisinone. Nitisinone produced an increase in tyrosine and catecholamine metabolite (HVA, VMA, and metanephrines) levels. Nitisinone may be a promising agent in metastatic neuroblastoma.     

Pediatric hepatocellular carcinoma in a developing country: Is the etiology changing?

HCC is the second most common malignant liver tumor of childhood. It typically affects children with a median age of 10–14 yr on background hepatitis B‐related liver disease and is often metastatic or locally advanced at diagnosis. Children below the age of five yr typically constitute <10% of all children with HCC. In these children, it occurs on a background of congenital or metabolic liver disease. The records of all children with HCC who presented to our department over a six‐yr study period were reviewed. Twelve patients with a median age of 5.9 yr (range 1.6–15.4) were diagnosed to have HCC. All patients underwent liver transplantation, and none were resected. Eleven patients had background congenital or metabolic liver disease. All five of those with hereditary tyrosinemia type 1 who presented to us were found to have HCC. No patient had hepatitis B‐related liver (HBV) disease. Eight (66.7%) patients had incidentally discovered HCC on examination of the explant. Incidentally discovered HCC were smaller, well differentiated, and did not show microvascular invasion compared to those diagnosed preoperatively. There was no recurrence with a median follow‐up of five months. The patient demographic for pediatric HCC is changing probably as a consequence of successful immunization against HBV. Younger patients with congenital and metabolic liver disease in whom liver transplantation is the ideal treatment are likely to constitute an ever‐increasing proportion of patients with pediatric HCC as HBV disease is controlled or eradicated.     

The efficacy of liver transplantation in malignant liver tumors associated with tyrosinemia: clinical and laboratory findings of five cases

To evaluate clinical and laboratory findings of these patients and the efficacy of liver transplantation in children with hepatocellular carcinoma (HCC) and hepatoblastoma (HB) associated with tyrosinemia. Among 113 children with liver tumors diagnosed between 1972 and 2004 five patients had HCC or HB associated with tyrosinemia. The age at diagnosis of the HCC or HB ranged from 9.5 to 17 yr and male:female ratio was 1:4. During regular clinic visits for tyrosinemia, elevated alpha-fetoprotein (AFP) was detected in all patients. AFP levels ranged between 13.7 and 29 340 IU/mL. Radiological studies including ultrasound, computed tomography and magnetic resonance imaging showed heterogeneous parenchyma and nodules in the liver. The patients did not have any metastatic disease. The time from diagnosis of tyrosinemia to HCC or HB ranged from 9.25 to 15.25 yr. Histopathologically, four patients have been diagnosed as HCC and one patient had HB. All patients were given chemotherapy including cisplatin and adriamycin. In three patients, living-related liver transplantation was performed. They had no treatment after transplantation. All of them are disease free. One patient was treated with chemotherapy and right hepatectomy. She had no suitable donor for living-related liver transplantation. Three months after completing chemotherapy, she had recurrent tumor in the left lobe of the liver and she died with progressive disease. The last patient whose parents were not suitable as donors for living-related liver transplantation is waiting for a deceased donor graft. All patients had limited disease to liver due to close clinical and radiological follow up for tyrosinemia. In these patients liver transplantation is curative both for liver tumor and tyrosinemia.     

Favorable outcome of primary liver transplantation in children with cirrhosis and hepatocellular carcinoma

The outcome of HCC after transplantation (OLT) in children is not well known. Unfavorable features based on adult reports may lead to contraindicate OLT even in children. We reviewed a cohort of children with cirrhosis and HCC to evaluate their outcome after primary transplantation. We considered children with cirrhosis and HCC who had a primary OLT. We retrospectively recorded demographic, medical and surgical features, and MC as predictors of outcome. Among 456 children transplanted in the last 15 yr, 10 (2%), median age at diagnosis 1.8 yr (range 0.5-7.2), had HCC in biliary atresia (3), BSEP deficiency (3), tyrosinemia type 1 (2), complications of choledocal cyst and glycogen storage disease type IV (1 each). At HCC discovery, median AFP was 2322 ng/mL (3-35,000), high or rising in 9/10 patients. Six patients were outside the MC. Median time on the waiting list was 38 days (1-152). Two patients died from early complications of OLT. In the other eight patients, there was no tumor recurrence after a median follow-up of four yr. Children with cirrhosis may develop HCC at a very young age. The outcome appears excellent even outside MC. Primary liver transplantation is advisable for children with cirrhosis, HCC, and no extrahepatic disease.     

Tyrosinemia: A Review

Hypertyrosinemia encompasses several entities, of which tyrosinemia type I (or hepatorenal tyrosinemia, HT1) results in the most extensive clinical and pathological manifestations involving mainly the liver, kidney, and peripheral nerves. The clinical findings range from a severe hepatopathy of early infancy to chronic liver disease and rickets in the older child; gradual refinements in the diagnosis and medical management of this disorder have greatly altered its natural course, mirroring recent advances in the field of metabolic diseases in the past quarter century. Hepatorenal tyrosinemia is the inborn error with the highest incidence of progression to hepatocellular carcinoma, likely due to profound mutagenic effects and influences on the cell cycle by accumulated metabolites. The appropriate follow-up of patients with cirrhosis, the proper timing of liver transplantation in the prevention of carcinoma, and the long-term evolution of chronic renal disease remain important unresolved issues. The introduction of a new pharmacologic agent, NTBC, holds the hope of significantly alleviating some of the burdens of this disease. Mouse models of this disease have permitted the exploration of newer treatment modalities, such as gene therapy by viral vectors, including ex vivo and in utero methods. Finally, recent observations on spontaneous genetic reversion of the mutation in HT1 livers challenge conventional concepts in human genetics. Received November 15, 2000; accepted December 7, 2000.     

Living donor liver transplantation for pediatric patients with metabolic disorders: The Japanese multicenter registry

LDLT is indicated for a variety of metabolic disorders, primarily in Asian countries due to the absolute scarcity of deceased donor LT. We analyzed data for all pediatric LDLTs performed between November 1989 and December 2010, during which 2224 pediatric patients underwent LDLT in Japan. Of these patients, 194 (8.7%) underwent LDLT for metabolic disorders. Wilson's disease (n = 59; 30.4%) was the most common indication in the patients with metabolic disorders, followed by OTCD (n = 40; 20.6%), MMA (n = 20; 10.3%), and GSD (n = 15; 7.7%). The one‐, five‐, 10‐, and 15‐yr patient and graft survival rates were 91.2%, 87.9%, 87.0%, and 79.3%, and 91.2%, 87.9%, 86.1%, and 74.4%, respectively. Wilson's disease and urea cycle deficiency were associated with better patient survival. The use of heterozygous donors demonstrated no negative impact on either the donors or recipients. With regard to X‐linked OTCD, symptomatic heterozygote maternal donors should not be considered potential donor candidates. Improving the understanding of the long‐term suitability of this treatment modality will require the registration and ongoing evaluation of all patients with inherited metabolic disease considered for LT.     

Liver transplantation may prevent neurodevelopmental deterioration in high‐risk patients with urea cycle disorders

UCDs are among the most common inherited metabolic diseases in Japan. We investigated the clinical manifestations, treatment, and prognoses of 177 patients with UCDs who were evaluated and treated from January 1999 to March 2009 in Japan, using a questionnaire survey. Among these 177 patients, 42 (seven with carbamoyl phosphate synthetase 1 deficiency, 27 with ornithine transcarbamylase deficiency, seven with argininosuccinate synthetase deficiency, and one with arginase 1 deficiency) underwent living‐donor LT. Although this study was retrospective and included limited neurodevelopmental information before and after LT, we evaluated whether LT could improve neurodevelopmental outcomes in patients with UCDs. The neurodevelopmental outcomes of patients with a MAC of <300 μmol/L at the time of onset were not significantly different between the LT and non‐LT groups (P=.222). LT may have prevented further neurodevelopmental complications in children with MAC ≥300 μmol/L (P=.008) compared with non‐transplant management. Therefore, Liver transplant should be considered in patients with UCD with a MAC of ≥300 μmol/L at the time of disease onset.     

Pediatric liver transplantation in metabolic disease: clinical decision making

Proper utilization of liver transplantation in the management of pediatric metabolic diseases requires a comprehensive understanding of both metabolic disease and the risk and benefits of transplantation. This brief review focuses on issues that pertain to the treatment of tyrosinemia type I, bile acid biosynthesis disorders, primary hyperoxaluria, Crigler-Najjar Type I, and mitochondrial diseases. These entities are used as prototypes to illustrate many of the principles that are applied in a more general sense to the management of metabolic diseases. The natural history of these disorders are considered in the context of the risks of liver transplantation. Indications, contraindications, and both current and future alternatives to transplantation, are considered.     

Tyrosinemia type 1 in Spain: Mutational analysis,treatment and long‐term outcome

Background: Tyrosinemia type 1 (HT1) is a rare but treatable disease. The aim of the present study was to review the efficacy of long‐term treatment of HT1 with nitisinone, expand knowledge about the clinical spectrum of the disease and assess a possible genotype–phenotype correlation. Methods: A retrospective multicenter study was carried out based on questionnaires on genotype, phenotype, therapy and outcome in 34 Spanish patients with HT1. Results: The main manifestations that led to the diagnosis were acute liver failure (55.8%), asymptomatic hepatomegaly (44.1%) and renal tubular dysfunction (29.4%). Laboratory analysis indicated a marked increase of α‐fetoprotein and coagulopathy. The most common mutation was IVS6‐1(G > T; 66.6% of 24/34 patients for whom mutation analysis was available) and these patients presented less nephrocalcinosis and more hepatomegaly at diagnosis; two novel mutations (c.974C>T, c.398A>T) were found. The mean duration of treatment was 6.73 years. Dietary compliance was very good in 47.1% and good in 20.6%; nitisinone treatment adherence was very good in 85.2% of cases. Mean dose of nitisinone was 0.87 mg/kg per day with average plasma levels of 45.67 µmol/L. Only one patient required liver transplantation after nitisinone and none had hepatocellular carcinoma. Conclusions: Treatment with nitisinone has improved the prognosis of HT1, and compliance is good. In Spain, screening for HT1 by plasma tyrosine and urine succinylacetone determination may be implemented with IVS6‐1(G > T) mutational analysis. A correlation between low frequency of nephrocalcinosis and IVS6‐1(G > T) mutation was observed.     

Liver transplantation for hereditary tyrosinemia type I: analysis of the UNOS database

Patients with HT-1 can develop progressive liver disease and have a high incidence of HCC. LT is indicated in patients with fulminant liver failure, HCC or decompensated chronic liver disease refractory to NTBC. To determine the need for LT and outcomes after LT in children with HT-1. Children with HT-1 who had LT between 10/1987 and 5/2008 were identified from the UNOS database. Of 11,467 children in the UNOS database, 125 (1.1%) required LT secondary to HT-1. Mean age at LT was two and half yr (s.d. ± 3.6 yr). Mean age at LT during the first 10 yr of the study (1.82, s.d. ± 2.86 yr) was significantly lower than in the last decade (3.70, s.d. ± 4.42 yr), p = 0.01. Nearly half of the patients (58, 46.4%) were transplanted between 1988 and 1992. Overall, one- and five-yr patient survival was 90.4% and 90.4%, respectively. LT is a valuable option for children with HT-1 with fulminant liver failure or when medical treatment fails. The rate of LT for children with HT-1 has decreased and age at transplant increased over the last decade most probably reflecting the effect of early diagnosis and treatment with NTBC.     

Early liver transplantation is indicated for tyrosinemia type I

Liver transplantation is now accepted as the treatment of choice for tyrosinemia type I (hereditary tyrosinemia). In an effort to determine whether any factors in these patients would aid in predicting optimal timing of the transplant procedure, we evaluated several clinical, biochemical, and radiographic parameters in five successive patients undergoing liver transplant for tyrosinemia type I at the University of Minnesota. All five patients evidenced prolonged periods of clinical and metabolic stability with dietary therapy and four of five remained stable at the time of evaluation for transplantation. Nevertheless, all five suffered significant and unexpected complications of tyrosinemia prior to the time of liver transplant. Four developed renal stones, two were in liver failure, and one developed a neurologic crisis that left him completely paralyzed. Hepatocellular carcinoma was found in one of the five at transplant. We could identify no clinical, biochemical, or radiographic study that was predictive of the likelihood of significant complications of the disorder. Survival from the transplant procedure itself was 100%. The inability to predict or prevent significant complications of tyrosinemia and the favorable outcome from transplantation lead us to recommend liver transplant for all patients with tyrosinemia type I by 12 months of age.     

Living‐donor liver transplantation for mild Zellweger spectrum disorder: Up to 17 years follow‐up

Mild Zellweger spectrum disorder, also described as Infantile Refsum disease, is attributable to mutations in PEX genes. Its clinical course is characterized by progressive hearing and vision loss, and neurodevelopmental regression. Supportive management is currently considered the standard of care, as no treatment has shown clinical benefits. LT was shown to correct levels of circulating toxic metabolites, partly responsible for chronic neurological impairment. Of three patients having undergone LT for mild ZSD, one died after LT, while the other two displayed significant neurodevelopmental improvement on both the long‐term (17 years post‐LT) and short‐term (9 months post‐LT) follow‐up. We documented a sustained improvement of biochemical functions, with a complete normalization of plasma phytanic, pristanic, and pipecolic acid levels. This was associated with stabilization of hearing and visual functions, and improved neurodevelopmental status, which has enabled the older patient to lead a relatively autonomous lifestyle on the long term. The psychomotor acquisitions have been markedly improved as compared to their affected siblings, who did not undergo LT and exhibited a poor neurological outcome with severe disabilities. We speculate that LT performed before the onset of severe sensorineural defects in mild ZSD enables partial metabolic remission and improved long‐term clinical outcomes.     

活体肝移植治疗Ⅰ型酪氨酸血症的疗效

目的 探讨活体肝移植治疗Ⅰ型酪氨酸血症(HT Ⅰ)的手术疗效和预后.方法 2013年7月至2015年5月,4例确诊为HT Ⅰ的患儿(3男1女)在我中心接受了活体肝移植手术,手术指征均为肝硬化失代偿及AFP过高.患儿术前Child分级:B级3例,C级1例.患儿中位手术年龄4.4岁(1.9～5.9岁),供体均为患儿父母.患儿术后中位随访时间17个月(9～24个月).结果 4例活体肝移植手术供、受体均手术顺利,术后恢复良好.患儿术后酪氨酸代谢恢复正常,异常代谢产物琥珀酰丙酮(SA)、琥珀酰乙酰乙酸(SAA)、延胡索酰乙酰乙酸(FAA)和马来酰乙酰乙酸(MAA)的血清水平下降到测不出水平,肝功能和AFP在随访期间都维持正常.术后电解质水平恢复正常,肾功能维持稳定.所有患儿术后均表现出追长趋势.并发症方面,1例患儿出现EBV病毒感染和急性排斥反应,1例患儿术后存在乳糜漏和反复腹水,1例患儿出院后6个月感染手足口病病毒,均得以治愈.结论 活体肝移植是治疗HTⅠ的有效方式,术后患儿的代谢异常、肝肾功能和AFP水平均恢复正常,其术后生存率令人满意,但长期随访应注意肾功能的检测.     

Surgical management of children and adolescents with upfront completely resected hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is an aggressive malignant neoplasm that is often chemoresistant. Complete surgical resection remains the mainstay of therapy. The role of liver transplantation (LT) in pediatric HCC is in evolution, as is the role of adjuvant chemotherapy for stage I disease.

Methods

A retrospective review of patients < 18 years of age with completely resected HCC treated with surgical intervention alone at our institution from 2004 to 2015 was conducted.

Results

Twelve patients with a median age of 12 years (range = 1–17; number of females = 7) with upfront resected HCC (Evans stage I) were identified. Four patients had HCC without identifiable risk factors (fibrolamellar‐HCC = 2; early HCC arising in focal nodular hyperplasia = 1, well‐differentiated [wd] HCC = 1). Four patients had early or wd‐HCC in the context of portosystemic shunts (Abernethy = 2; mesocaval shunt and portal vein thrombosis = 2). Four patients had moderate to wd‐HCC in the context of pre‐existing liver disease with cirrhosis (progressive familial intrahepatic cholestasis type‐2 = 2, alpha‐1 antitrypsin deficiency = 1, Alagille syndrome = 1). Seven patients underwent LT (multifocal = 5; solitary = 2); five exceeded Milan criteria (MC) by imaging. Five patients underwent complete resection (segmentectomy = 2; hemihepatectomy = 3). Ten patients received no adjuvant chemotherapy. All patients are alive without evidence of disease with a median follow‐up of 54.1 months (range = 28.1–157.7 months).

Conclusions

Pediatric and adolescent patients with upfront, completely resected HCC can be effectively treated without chemotherapy. LT should be considered for nonmetastatic HCC, especially in the context of pre‐existing chronic liver disease, even when the tumor exceeds MC. Distinct pediatric selection criteria are needed to identify patients most suitable for LT.

     

Hepatocellular carcinoma in children and effect of living-donor liver transplantation on outcome

Hepatocellular carcinoma (HCC) is primarily observed in the older children and in most cases it develops in association with liver cirrhosis. Liver transplantation offers a good chance for long-term cure. To evaluate the outcome of children with HCC and the impact of living-donor orthotopic liver transplantation (OLT) on survival a retrospective review of radiographic, laboratory, pathologic, and therapeutic data in 13 children (six female and seven male) with chronic liver disease accompanied with HCC were studied. The patients were divided into two groups according to therapeutic modality: transplanted and non-transplanted patients. Kaplan-Meier survival curves in various therapeutic groups were plotted. The mean age of patients was 6.4 +/- 4.8 yr. Pediatric end-stage liver disease score was adapted to model for end-stage liver disease score for HCC and ranged between 1-44 and 18-44, respectively. The underlying liver diseases were tyrosinemia type 1 (n = 6), chronic hepatitis B infection (n = 6), glycogen storage disease type 1 (n = 1). Alfa-feto protein levels were elevated in all patients except one. Median number of tumor nodules was three (1-10), median maximal diameter of tumor nodules was 3.4 cm (0.5-8). Eleven patients were eligible for OLT whereas two patients were not eligible. Seven of the 11 patients considered for transplantation underwent living-donor OLT. Remaining four patients died while waiting on cadaveric transplant list. Overall 1 and 4-yr survival rates for all patients were 53.3 and 26.6%, respectively, and were found significantly higher in transplanted children than non-transplanted children (72%, 72% vs. 33% and 16.6%). No patient had tumor recurrence at median of 36-month follow-up after OLT. OLT is a life-saving procedure for children with chronic liver disease accompanying with HCC. Living-donor OLT avoids the risk of tumor progression and transplant ineligibility in these children.     

Liver transplantation for neonatal‐onset citrullinemia

Citrullinemia or ASS deficiency in its classical form presents in the neonatal period with poor feeding, hyperammonemia, encephalopathy, seizures, and if untreated can be fatal. Despite advances in medical therapy, neurocognitive outcomes remain suboptimal. LT has emerged as a potential management option. A retrospective single‐center review identified 7 children with a median age of 1.1 years (range, 0.6‐5.8) at referral. Five children presented clinically, and 2 were treated prospectively from birth due to positive family history. All patients received standard medical and dietary therapy prior to LT. The indications for LT were frequent metabolic decompensations in 4, elective in 2, and ALF in 1. The median age at LT was 2.4 years (range, 1.3‐6.5). Five patients received 6 left lateral segment grafts, one a live unrelated donor left lateral segment as an APOLT graft, and one a cadaveric whole liver graft as APOLT. One child required retransplantation due to hepatic artery thrombosis. Graft and patient survival were 86% and 100%, respectively. Median follow‐up is 3.1 years (range, 0.1‐4.1), and the median age at follow‐up is 5.5 years (range, 4.0‐9.8). There have been no metabolic decompensations in 6 children, while 1 patient (with APOLT) developed asymptomatic hyperammonemia with no clinical or histological signs of liver injury, requiring additional medical therapy. Our medium‐term experience following LT in citrullinemia is favorable, demonstrating a positive transformation of the clinical phenotype.     

Liver transplantation for homozygote familial hypercholesterolemia: the only curative treatment

FH is an autosomal dominant genetic disorder characterized by increased TC and LDL level, which leads to xanthomas, atherosclerosis, and cardiac complications even in childhood. The treatment options are diet, medical treatment, lipid apheresis, and LT. The aim of our study was to analyze our data of patients with FH. Between 2004 and 2015, there were 51 patients who underwent pediatric LT at our center. All patients with FH were identified, and the data were retrospectively analyzed. There were eight patients with homozygous FH in the median age of 10 years (IQR 6–12) who underwent LT. The median pre‐operative TC and LDL levels were 611 mg/dL (IQR: 460–844) and 574 mg/dL (IQR: 398–728) and decreased to normal levels 1 week after LT (TC: 193 mg/dL and LDL: 141 mg/dL). Two patients died two and 18 months after LT due to sudden cardiac arrest. Both patients were diagnosed with cardiovascular disease pre‐operatively. The LT is the only curative treatment for this disease. To achieve an excellent outcome, it should be performed before the development of cardiovascular disease, because the regression of severe cardiovascular disease after transplantation is limited.     

Heart Rate Variability in Children With Fontan Circulation: Lateral Tunnel and Extracardiac Conduit

The technique in Fontan surgery has developed from the lateral tunnel (LT) toward the extracardiac conduit (EC) used to reduce long-term complications such as atrial arrhythmia and sinus node dysfunction. Heart rate variability (HRV) examines cardiac nervous activity controlling the sinus node. This study aimed to investigate HRV in a cohort of children with univentricular hearts, focusing on the relation between HRV and surgical procedure. For 112 children with Fontan circulation, HRV was analyzed using power spectral analysis. Spectral power was determined in three regions: very-low-frequency (VLF), low-frequency (LF), and high-frequency (HF) regions. Patients were compared with 66 healthy controls subject. Patients with LT were compared with patients who had EC. The children with Fontan circulation showed a significantly reduced HRV including total power (P < 0.0001), VLF (P < 0.0001), LF (P < 0.0001), and HF (P = 0.001) compared with the control subjects. The LT and EC patients did not differ significantly. Reduced HRV was found in both the LT and EC patients. In terms of HRV reduction, EC was not superior to LT.     

HEREDITARY TYROSINEMIA

The clinical and biochemical findings in the case of an infant with hereditary tyrosinemia followed from birth have been reported. The child received a low protein diet from birth and a formula diet restricted in phenylalanine and tyrosine when the diagnosis was established at 54 days of age. There was a steady progress of the disease and the baby died from liver failure complicated with septicemia when he was 5½ months old. The clinical course and the biochemical findings as well as the morphological changes were typical of the acute type of the disease. A 6½ year old brother suffers from the same disease of the chronic type and the two types of hereditary tyrosinemia therefore seem to belong to the same genotype. The biochemical data from the patient with hereditary tyrosinemia have been compared with those in a healthy looking baby with longstanding and pronounced transient tyrosinemia of early infancy. The patterns of amino acids in blood and of phenolic acids in urine were similar in the two patients and it is concluded that an early laboratory differential diagnosis between hereditary tyrosinemia and transient tyrosinemia may only be made by observing the biochemical response to a diet restricted in tyrosine and phenylalanine in combination with the results of phenylalanine tolerance tests. The clinical features of hereditary tyrosinemia can apparently not be attributed to a high serum-tyrosine concentration or to the overproduction of phenolic acids; the lack of effect of early restriction in the intake of phenylalanine and tyrosine indicates a more complex pathogenesis of hereditary tyrosinemia than a primary deficiency of p-hydroxyphenylpyruvate hydroxylase.