Tyrosinemia I,a model for human diseases mediated by 2-oxoacid-utilizing dioxygenases: hepatotoxin suppression by NTBC does not normalize hepatic collagen metabolism

OBJECTIVES: Medical treatment of tyrosinemia I relies on the herbicide NTBC [Orfadin 2-(2-nitro-4-trifluoromethylbenzoyl)-cyclohexane-1,3-dione], an inhibitor of plant and mammalian 2-oxoacid-utilizing dioxygenases with a collective catalytic cycle ('HAG' mechanism). We hypothesize that NTBC-treated tyrosinemia I is a human model for the pathogenic role of two major enzymes in this class, 4-hydroxyphenylpyruvate dioxygenase (4-HPPD; EC 1.13.11.27) and prolyl 4-hydroxylase (P4-H; E.C. 1.14.11.2), essential for tyrosine and collagen metabolism, respectively. METHODS: In a patient with established tyrosinemia I, we monitored the in vivo activities of 4-HPPD and P4-H via five biomarkers before and during NTBC medication. Hypothesis testing at the molecular level was performed by computational modeling of NTBC binding to the crystal structure-derived active site of 4-HPPD, and then relating these findings to our experimental results and to known P4-H data. RESULTS: NTBC rapidly normalized the biomarkers for 4-HPPD activity. However, those for P4-H activity remained uniformly elevated after one hundred days on NTBC, the PIIINP biomarker even increasing above its grossly abnormal, initial level. This selective enzyme inhibition despite a collective catalytic cycle is attributed to the conformation of NTBC, which only fits the active site of 4-HPPD, as confirmed by its crystal structure. CONCLUSIONS: Normalization of hepatic collagen formation, highly desirable in all fibrotic liver diseases, is not achieved by NTBC in tyrosinemia I. By establishing the molecular cause for this failure, our results also establish a rational approach to identify inhibitors that achieve that goal, either by joint 4-HPPD / P-4H inhibition, or by inhibition of only P-4H.     

Favorable outcome of treatment with NTBC of acute liver insufficiency disclosing hereditary tyrosinemia type I]

BACKGROUND: Hereditary tyrosinemia type I is a disease with a severe prognosis. Main causes of death are acute liver failure, neurologic crises and hepatocarcinoma. NTBC, which acts as an inhibitor of the 4-hydroxyphenylpyruvate dioxygenase, prevents the formation of toxic metabolites involved in hepatic, renal and neurologic lesions. CASE REPORTS: Results of NTBC therapy used in three infants with type I tyrosinemia who presented with acute liver failure are reported. The diagnosis relied on the finding of high plasmatic levels of tyrosine and methionine, and abnormal urinary excretion of succinyl acetone and delta aminolevulinic acid. Treatment with NTBC was initiated within 2 to 8 days from onset of symptoms. Signs of liver failure resolved after 3 weeks therapy. After 12 to 39 months of follow-up, outcome remains favorable. CONCLUSION: The results reported here highlight the efficiency of NTBC in type I tyrosinemia with early acute onset. However, the long term outcome needs to be determined with regards to prevention of hepatocarcinoma and toxicity of the drug.     

Clinical practice

Four patients with tyrosinemia type 1 (ages 6–32 months) were treated with 2-(2-nitro-4-trifluoro-methylbenzoyl)-1,3-cyclohexandion (NTBC) at Cairo University Children’s Hospital, Egypt and followed up for 12–27 months. The recommended average dose of NTBC is 1 mg/kg/day. They were started on the following doses: 0.8, 0.58, 0.5, and 0.625 mg/kg/day, respectively. Two months after start of therapy, succinylacetone was undetectable in patients 1, 2, and 4, while in case 3, it was 5.4 μM. Her NTBC dose was increased from 0.5 to 0.65 mg/kg/day, and succinylacetone was undetectable 1 month later. They were kept on NTBC doses ranging from 0.55 to 0.65 mg/kg/day. These doses allowed catch up growth, normalization of synthetic liver functions, steep drop in serum alpha fetoprotein, reduction in phosphate loss in urine, normalization of serum calcium, phosphate, and alkaline phosphatase, and healing of active rickets. Succinylacetone was undetectable in urine on these doses. In conclusion: Doses of NTBC, lower than recommended, may be helpful in treatment of tyrosinemia, on condition that succinylacetone production is suppressed, and AFP is maintained normal or showing a progressive decrease. This cost-effective dose may allow treatment of affected children from economically underprivileged countries, but longer follow up periods are needed.     

Hereditary tyrosinemia type 1 from a single center in Egypt: clinical study of 22 cases

Background  

Hereditary tyrosinemia type 1 (HT1) is an increasingly recognized inborn error of metabolism among Egyptian children. This study was undertaken to define the presenting clinical, biochemical and imaging features and outcome of 2-(2-motrp-4-trifluoromethylbenzoyl)-1, 3-cyclohexanedione (NTBC) therapy and liver transplantation in a cohort of Egyptian children diagnosed with HT1.     

Serum type III procollagen in children with type I hereditary tyrosinemia.

BACKGROUND: Type I hereditary tyrosinemia leads to hepatic dysfunction and fibrosis and is associated with a high risk of hepatic malignancy. Serum N-terminal propeptide of type III procollagen is a sensitive marker of organ fibrosis of diverse origins. The current study was conducted to determine whether analysis of serum levels of type III procollagen in hereditary tyrosinemia would be useful in the follow-up of the progressive liver disease and eventually in detecting hepatic malignancy. METHODS: Serum N-terminal propeptide of type III procollagen was sequentially studied in 10 children with type I hereditary tyrosinemia. RESULTS: At diagnosis of type I hereditary tyrosinemia, serum N-terminal propeptide of type III procollagen ranged from 0.6 to 2.9 multiples of age-related median. During follow-up, serum N-terminal propeptide of type III procollagen decreased, yet remained elevated 0.2 to 2.6 years after diagnosis. Children with the acute type of the disease tended to have higher serum N-terminal propeptide of type III procollagen than did those with the chronic type. Porphyria crises were associated with elevated serum type III procollagen. The one patient receiving 2-(2-nitro-4-trifluoromethyl-benzoyl)-1,3-cyclohexanedione (NTBC) did not differ from the other ones in serum type III procollagen levels. Serum N-terminal propeptide of type III procollagen did not increase with developing hepatocellular carcinoma. CONCLUSIONS: Serum N-terminal propeptide of type III procollagen may be useful in monitoring the hepatopathy in type I hereditary tyrosinemia but is not useful in detecting malignant transformation in the liver.     

Kidneys of mice with hereditary tyrosinemia type I are extremely sensitive to cytotoxicity

Children with hereditary tyrosinemia type 1 (HT1) suffer from liver failure, renal tubular dysfunction, and rickets. The disease is caused by deficiency of fumarylacetoacetate hydrolase (FAH), the last enzyme of tyrosine catabolism, and leads to accumulation of the toxic substrate fumarylacetoacetate (FAA) in hepatocytes and renal proximal tubular cells. Patients are treated with 2-(2-nitro-4-trifluoro-methylbenzoyl)-1,3 cyclohexanedione (NTBC), which prevents accumulation of FAA by blocking an enzyme upstream of FAH. Liver transplantation is performed when patients do not respond to NTBC or develop hepatocellular carcinoma. This reduces the tyrosine load for the kidney but does not abolish renal exposure to locally produced FAA. To investigate the pathogenesis of liver and kidney damage induced by tyrosine metabolites, we challenged FAH-deficient mice with various doses of homogentisic acid (HGA), a precursor of FAA. Injecting NTBC-treated Fah-/- mice with low doses of HGA caused renal damage and death of renal tubular cells, as was shown by histologic analyses and deoxynucleotidyl transferase-mediated dUDP nick-end labeling (TUNEL) assay but did not lead to liver damage. In addition, kidney function, but not liver function, was affected after exposure to low doses of HGA. Administration of high doses of HGA led to massive cell death in both the liver and kidneys. Resistance to HGA-induced cell death was seen after withdrawing NTBC from Fah-/- mice. The finding that the kidneys of Fah-/- mice are especially sensitive to damage induced by low doses of HGA underscores the need to perform careful monitoring of the kidney function of tyrosinemia patients undergoing any form of treatment.     

Reversibility of cirrhotic regenerative liver nodules upon NTBC treatment in a child with tyrosinaemia type I

In a male patient with hereditary tyrosinaemia type I (HTI), NTBC [2-(2-nitro-4-trifluoro-methylbenzoyl)-1,3-cyclohexandion] treatment and a diet low in phenylalanine and tyrosine were started at the age of 4 wk. At the recommended average dosage (1 mg kg(-1)), liver failure improved transiently. After 4 mo of treatment, with increased body weight, the dose had decreased to 0.7 mg kg(-1), and diffuse cirrhotic changes in liver parenchyma and multiple nodules were visualized by ultrasonography. Multiple nodules in the liver parenchyma were differentiated from hepatocellular carcinoma by magnetic resonance imaging (MRI) using mangafodipir trisodium as a paramagnetic liver-specific contrast agent. Augmentation of NTBC dosage resulted in a decrease in serum alpha-fetoprotein levels and in significant regression of liver nodules on MRI. CONCLUSION: In HTI patients with a poor response to NTBC treatment and/or development of cirrhotic changes of liver parenchyma, augmentation of the recommended NTBC dosage may result in significant improvement of symptoms.     

Experience with NTBC therapy in hereditary tyrosinaemia type I: an alternative to liver transplantation

We present the clinical data of five infants with type I (hepato-renal) tyrosinaemia on NTBC therapy. All presented initially at the local hospital in the 1st year of life with progressive abdominal distension owing to hepato-splenomegaly and with radiological evidence of liver cirrhosis, except for one child who was diagnosed during screening because of an affected sibling. Age at commencement of NTBC therapy ranged from 6 to 30 months. All infants showed remarkable improvement within 2-6 months of starting NTBC treatment, except one who died 2 months after commencement of therapy from uncontrolled liver failure, severe coagulopathy and Streptococcus pneumoniae septicaemia. NTBC treatment along with a phenylalanine- and tyrosine-restricted diet has effectively reversed most clinical manifestations of this disease. To date, none of our patients has developed hepatic carcinoma and NTBC was well tolerated without side-effects. NTBC is costly but life-saving and is an obvious alternative to more hazardous liver transplantation.     

Rapid improvement in the renal tubular dysfunction associated with tyrosinemia following hepatic replacement.

The postoperative management of patients with hereditary tyrosinemia type I (McKusick 27670) following liver transplantation is often complicated by the renal tubular dysfunction associated with this disease. To characterize better the temporal course of the improvement in renal excretory activity following hepatic replacement, renal tubular function and metabolite excretion were studied in a 4-year-old girl with hereditary tyrosinemia during the immediate post-transplantation course. Tubular reabsorption of bicarbonate and phosphate were normal 5 days following transplantation, in contrast to glucosuria, hyperaminoaciduria, and tyrosyluria, which persisted for approximately 3 weeks. After hepatic replacement, serum amino acid concentrations returned to normal and succinylacetone was no longer detected in the urine. This is the third tyrosinemia patient reported to achieve complete resolution of urinary abnormalities following transplantation, and the only patient in whom renal tubular function was formally assessed within the first postoperative week.     

Indications and outcome of liver transplantation in tyrosinaemia type 1

A retrospective analysis was performed on 17 patients presenting with tyrosinaemia type 1 (TT1) between 1989-1997; 7 pre 1992 prior to the introduction of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) therapy and 10 post 1992. During this time, eight children (5 males) underwent orthotopic liver transplantation (OLT); six prior to the introduction of NTBC in 1992 and two on NTBC therapy. The primary indications for OLT pre-1992 were risk of hepatocellular carcinoma with evidence of hepatic dysplasia in all, associated with liver failure in two, and rise in !-fetoprotein (AFP) in four. Two of the ten treated with NTBC required OLT. The indications were non-response to NTBC in one child and development of hepatic dysplasia associated with poor quality of life in the second patient. Median age for OLT was 64 months (range 5-127 months) with a median weight of 24 kg (range 6-25 kg). The histology of hepatectomy specimens at transplantation showed: cirrhosis in 8, hepatic dysplasia in 6 and hepatocellular carcinoma in 1. Plasma tyrosine and AFP returned to normal in all cases. Urinary succinylacetone reduced but persisted in small amounts (median 7.7 7mol/mmol creatinine). Hypertrophic cardiomyopathy resolved in 3/3 patients. Hypoglycaemia, not responding to dietary therapy or NTBC treatment, resolved post-transplant in one patient. There were two deaths, one from primary non-function and one from chronic rejection. Late complications in survivors (n=6) include post-transplant lymphoproliferative disease of the iris in one child which resolved and renal dysfunction with a fall in glomerular filtration rate in three (50%). Median follow up post OLT is 6.7 years (range 1-7 years). Quality of life post-transplant in survivors is good with unrestricted diet in all. Conclusion Liver transplantation is an effective treatment for TT1 with good quality of life. The current indications of OLT in TT1 are non-response to NTBC, risk of malignancy and poor quality of life related to dietary restriction and frequency of blood sampling.     

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.     

Elevated plasma bile acid concentrations in two sisters with tyrosinaemia type I

A 21-month-old girl suffering from tyrosinaemia type I and undergoing treatment with 2-(2-nitro-4-trifluoro-methylbenzoyl)-1,3-cyclohexanedione (NTBC) presented with pruritus which rapidly ceased with administration of high doses of ursodeoxycholic acid. Determination of plasma bile acids revealed clearly elevated levels both in samples taken before and after the onset of NTBC therapy, thus indicating, that the increase was not related to the administration of this drug. This result is corroborated by data from the first patient's newborn sister, diagnosed with the same disease, who showed elevated plasma bile acid concentrations in all samples examined, except for the cord plasma. This is the first report on altered bile acid concentrations in tyrosinaemia type I, and underlines the need for thorough investigation of bile acid metabolism in this disease.     

Tyrosinämie Typ I Klinische und biochemische Symptome bei 3 Säuglingen

Background. Tyrosinemia type I is an autosomal recessively inherited deficiency of fumarylacetoacetate hydrolase resulting in accumulation of tyrosin and its degradation products (succinylacetoacetone mainly). Typical clinical features include liver and kidney failure as well as central nervous system involvement. There are three main forms of the disease: the acute form with manifestation in newborn infants and the subacute and the chronic form in children older than one year of age. Case reports. We report on three infants with acute tyrosinemia type 1. In two patients impaired liver function with coagulopathy, hypalbuminemia and low cholinesterase as well as renal tubulopathy with urinary phosphate loss led to the diagnosis. In one patient high galactose and phenylalanine levels at routine neonatal screening gave the hint for further investigations. All patients had anemia and thrombocytopenia. Diagnosis was established by measurement of urinary succinylacetoacetone at mean age of 54.6 days. Treatment. Treatment with 2-(nitro-4-trifluoromethylbenzoyl)-1–3-cyclohexanedione (NTBC) and a diet low in tyrosine, and phenylalanine was started. Clinical improvement and normalization of laboratory findings were noted in all patients. Discussion. Tyrosinemia type I must be considered in newborns and infants with impaired hepatic synthesis of coagulation parameters, albumin and cholinesterase and with additional signs of renal tubulopathy (hypophosphatemia and rickets mainly). For diagnosis measurements of urinary succinylacetoaceton is essential.     

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.     

血尿琥珀酰丙酮检测在酪氨酸血症-Ⅰ型诊断中的应用

目的 探讨血、尿琥珀酰丙酮检测在酪氨酸血症-Ⅰ型诊断中的价值.方法 对临床疑似酪氨酸血症、血串联质谱检测酪氨酸水平增高的190例患儿,进行血串联质谱琥珀酰丙酮检测、尿气相色谱-质谱琥珀酰丙酮及有机酸检测.确诊条件为临床表现、血酪氨酸增高及血或尿琥珀酰丙酮增高.结果 确诊酪氨酸血症-Ⅰ型患儿11例,男9例,女2例,年龄2个月至6岁.患儿血琥珀酰丙酮显著升高( 14.2±7.8) μmol/L(参考值1～5μmol/L).其中7例患儿进行了尿气相色谱-质谱琥珀酰丙酮检测,4例阳性,3例阴性.血酪氨酸水平为(327.3±125.8) μmol/L(参考值为20 ～ 100μmol/L).临床表现均有肝肿大.结论 血或尿琥珀酰丙酮升高是诊断酪氨酸血症-Ⅰ型的最重要依据.串联质谱检测血琥珀酰丙酮较气相色谱-质谱检测尿琥珀酰丙酮对诊断酪氨酸血症-Ⅰ型更可靠,气相色谱-质谱尿琥珀酰丙酮检测可能导致假阴性.     

Contribution of extrahepatic tissues to biochemical abnormalities in hereditary tyrosinemia type I: study of three patients after liver transplantation

Three patients with hereditary tyrosinemia type I were examined before and after liver transplantation to assess the role of extrahepatic tissues in the biochemical disorders of this disease. Before transplantation the three patients excreted excessive amounts of succinylacetoacetate (SAA), succinylacetone (SA), tyrosyl acidic compounds, and 5-aminolevulinate (ALA). The activity of 5-aminolevulinate dehydratase (ALA-D) in red blood cells was markedly inhibited (1% to 5% of control) in the three patients. Successful liver transplantation resulted in decreased excretion of urinary SAA plus SA, tyrosyl acidic compounds, and ALA. Two of the patients continued to excrete significant amounts of SAA plus SA, whereas those compounds were undetectable in the urine of the third patient. Tyrosine loading resulted in increased excretion of SAA plus SA in two patients, but those compounds remained undetectable in the third. All three patients continued to excrete higher than normal amounts of ALA, but the activity of ALA-D in red blood cells returned to normal after transplantation, indicating marked clearance of SA from the blood. Liver transplantation may not totally correct the biochemical abnormalities of hereditary tyrosinemia. It is likely that the kidney is the source of persistent biochemical aberrations in the urine without significant effects on the blood. Our results suggest the existence of heterogeneity for renal involvement in hereditary tyrosinemia.     

Experience of a Single Center in NTBC Use in Management of Hereditary Tyrosinemia Type I in Libya

Background:

Hereditary Tyrosinemia type I (HTI) is a metabolic disease caused by deficiency of fumarylacetoacetate hydrolase enzyme.

Objectives:

This study reports beside its clinical and biochemical presentation, the outcome of NTBC [2- (2-nitro-4-trifloro-methylbenzoyl)-1, 3-cyclohexanedion] treatment of the disease and evaluates its biochemical markers in 16 pediatric Libyan patients.

Patients and Methods:

The diagnosis was based on presence of high tyrosine levels in blood and succinylacetone in urine.

Results:

The consanguinity rate was 81.2%, the median age at onset, at diagnosis and at starting treatment were 4.5, 8, and 9.5 months respectively. At presentation hepatomegaly, jaundice, rickets and high gamma glutamyl transferase (GGT) were observed in 87.5% of patients. All patients had extremely high alpha fetoprotein (AFP) and high alkaline phosphatase (ALP) levels. Fifteen patients were treated with NTBC, normalization of PT (Prothrombine time) was achieved in average in 14 days. The other biochemical parameters of liver function (transaminases, GGT, ALP, bilirubin and albumin) took longer to improve and several months to be normalized. Survival rate with NTBC was 86.6%. Patients who started treatment in a median of 3 months post onset observed a fast drop of AFP in 90.6% of patients (P = 0.003). Abnormal liver function and rickets were the common presentations, GGT was an early cholestatic sensitive test. ALP was constantly high even in asymptomatic patients.

Conclusions:

In HT1 a faster dropping of AFP is a marker of good prognosis.     

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.     

Diagnostic Problems of Disorders of Tyrosine Metabolism

Abnormalities of tyrosine metabolism have been reported in infants and children with a variety of liver diseases. Especially infants with hereditary fructose intolerance show often the very similar picture of clinical symptoms with congenital tyrosinemia. The livers of the patients, two cases of congenital tyrosinemia type 1 and three cases of hereditary fructose intolerance, were studied biochemically and compared to normal control livers. Kinetic studies of p-hydroxyphenylpyruvate oxidase revealed that crude extract of livers from patients with congenital tyrosinemia were distinctively inhibited by substrate in low concentration. It is suggested that this kinetic abnormality is closely related to the fundamental defect of congenital tyrosinemia. Activity of p-hydroxyphenylpyruvate oxidase was noted in peripheral leucocytes. The patient showed a reduced activity as low as 20% of normal. Enzyme assay in leucocytes might be useful in making the definite diagnosis prior to starting correct diagnosis for tyrosinemic state.     

Hereditary tyrosinemia of chronic course without rickets and renal tubular dysfunction

Three patients with hereditary tyrosinemia type 1, two brothers and one girl, studied at the age of 5, 12 and 15 years, respectively, had neither generalized hyperaminoaciduria, glucosuria nor clinical symptoms of rickets. Untreated the elder brother had only slightly elevated plasma tyrosine level (141 mumol/l, normal less than 80), and low excretion of p-hydroxyphenyllactate. He presented with pronounced thrombocytopenia (3 X 10(9)/l). At 13 years of age he contracted hepatocellular carcinoma. The younger brother presented with serum tyrosine of 318 mumol/l and thrombocyte count 48 X 10(9)/l. Succinylacetone in urine was elevated in both, 30 and 79 mumol/mmol creatinine, respectively. The female patient was investigated for hepatomegaly in infancy, atypical tyrosinemia being considered, but afterwards developed normally without diet or any other treatment until she contracted hepatoma at the age of 15 years. Her plasma tyrosine level was 600-700 mumol/l, and she excreted large amounts of p-hydroxyphenyllactate. Succinylacetone in urine was low but elevated (8 mumol/mmol creatinine). The fumarylacetoacetase activity in fibroblasts from the brothers and in lymphocytes from the girl was less than 5% and 10% of control levels, respectively. In conclusion, the chronic form of hereditary tyrosinemia may occur without evidence of renal tubular dysfunction.