Urinary Free Metanephrines for Diagnosis of Pheochromocytoma and Paraganglioma

BACKGROUND

Pheochromocytoma and paraganglioma (PPGL) is diagnosed through biochemical confirmation of excessive catecholamines in urine and plasma. Recent technological developments have allowed us to measure urinary free metanephrines; however, the diagnostic accuracy of these new methods and the diagnostic cutoff values have not been evaluated.

METHODS

This is a retrospective study of 595 subjects, including 71 PPGL cases and 524 controls. PPGL was based on pathological confirmation. Subjects with no evidence of PPGL over 2 years were included in the control group.

RESULTS

Urinary free metanephrines yielded similar area under the curve (AUC) to urinary fractionated metanephrines and plasma free metanephrines. However, urinary free normetanephrine yielded a better AUC than did urinary fractionated normetanephrine. The optimal cutoff for urinary free metanephrine and normetanephrine corrected for urinary creatinine yielded 97.2% sensitivity and 98.1% specificity.

CONCLUSION

Urinary free metanephrines are a reliable method for diagnosing PPGL in Asian populations compared with existing biochemical methods.

Extremely elevated international normalized ratio of warfarin in a patient with CYP2C9*1/*3 and thyrotoxicosis

A 73-yr-old Korean man with permanent atrial fibrillation visited outpatient clinic with severely increased International Normalized Ratio (INR) values after taking a usual starting dosage of warfarin to prevent thromboembolism. We found out later from his blood tests that he had hyperthyroidism at the time of treatment initiation. His genetic analysis showed CYP2C9*1/*3 and VKORC1+1173TT genotypes. We suspect that both hyperthyroidism and genetic variant would have contributed to his extremely increased INR at the beginning of warfarin therapy. From this case, we learned that pharmacogenetic and thyroid function test might be useful when deciding the starting dosage of warfarin in patients with atrial fibrillation.

Dried Blood Spot Multiplexed Steroid Profiling Using Liquid Chromatography Tandem Mass Spectrometry in Korean Neonates

BACKGROUND

Screening for congenital adrenal hyperplasia (CAH) using immunoassays for 17α-hydroxyprogesterone generates many false-positive results. We developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for simultaneous quantification of nine steroid hormones in dried blood spot (DBS) samples, and established reference intervals for these hormones.

METHODS

We examined our method for linearity, precision, accuracy, extraction recovery, and matrix effects and determined the reference intervals of cortisol, 17α-hydroxyproges-terone, 11-deoxycortisol, 21-deoxycortisol, androstenedione, corticosterone, 11-deoxycorticosterone, testosterone, and progesterone in 1,146 DBS samples (from 272 preterm and 874 full-term neonates). Immunoassay and LC-MS/MS methods were compared for 17α-hydroxyprogesterone. Fourteen additional samples were tested to validate the clinical applicability of the LC-MS/MS method.

RESULTS

The linearity range was 2.8-828.0 nmol/L for cortisol and 0.9-40.0 nmol/L for the other steroids (R²>0.99). Intra-day and inter-day precision CVs were 2.52-12.26% and 3.53-17.12%, respectively. Accuracy was 80.81-99.94%, and extraction recovery and matrix effects were 88.0-125.4% and 61.7-74.2%, respectively. There was a negative bias, with higher values measured by immunoassay compared with LC-MS/MS (r=0.8104, P<0.0001). The LC-MS/MS method was successfully applied to the analysis of nine steroids in DBS for screening and diagnosis of CAH using the 14 additional samples.

CONCLUSIONS

Our method enables highly sensitive and specific assessment of nine steroids from DBS and is a promising tool for clinical analysis of CAH.

Author Correction: Machine Learning Classifies Core and Outer Fucosylation of N-Glycoproteins Using Mass Spectrometry

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Therapeutic drug monitoring of mirtazapine in a routine outpatient setting in Asian psychiatric patients

INTRODUCTION

Mirtazapine is an antidepressant that acts by enhancing serotonergic and noradrenergic neurotransmission. This study aimed to evaluate mirtazapine pharmacokinetic data from Korean psychiatric patients and to identify the potential factors affecting its steady-state concentration.

METHODS

A total of 337 samples of steady-state mirtazapine concentrations from 188 adult psychiatric outpatients were retrospectively evaluated. Serum mirtazapine concentrations were measured by high-performance liquid chromatography-tandem mass spectrometry.

RESULTS

Median mirtazapine concentration was 43.6 μg/L (164.37 nmol) at a daily dosage range of 7.5-60 mg. At the steady state, mirtazapine dose had a positive correlation with the drug concentration. Mean concentration-to-dose (C/D) ratio was 1.48 μg/L/mg/day (5.58 nmol/mg/day), which was higher than that in a previous study in Caucasian subjects. Age and paroxetine co-medication were positively associated with C/D ratio. Initial mirtazapine concentration and C/D ratio did not show an association with responsiveness in depressive patients.

DISCUSSION

This study presented the therapeutic drug monitoring data for mirtazapine and pharmacokinetic variations of mirtazapine in an Asian population. A further study could be helpful for clinical decision making based on the characteristics of patients.

Weight-based vancomycin loading strategy may not improve achievement of optimal vancomycin concentration in patients with preserved renal function

We performed a retrospective study to evaluate clinical effectiveness of vancomycin loading strategy and factors associated with achieving optimal C min. Patients administered vancomycin for ≥72 h from January to June 2018 were enrolled. Patients were divided into two groups: loading (LD) and non-loading (NLD). LD was defined as initial vancomycin dose ≥20 mg/kg and ≥120% of maintenance dose. During study period, 70 and 71 received initial LD (24.2 ± 2.5 mg/kg) and NLD (17.3 ± 3.3 mg/kg) doses of vancomycin, respectively (p < .001). Achievement of optimal C min was not different before administration of the third dose (24.4% in LD versus 18.2% in NLD, p = .484) and within 72 h (22.9% versus 28.2%, p = .759). Risk factors for failure to achieve optimal C min before administration of the third dose were higher creatinine clearance and higher level of serum albumin. Therefore, more sufficient loading or patient-specific dose strategies should be used to achieve optimal serum vancomycin C min.

The Identification of a Novel Thiopurine S-Methyltransferase Allele, TPMT*45, in Korean Patient with Crohn's Disease

Pediatric Crohn's disease (CD) carries a higher genetic susceptibility and an increased risk of a more aggressive disease course than adult CD. Treatment of CD is based on immunomodulatory drugs, such as thiopurines. The enzyme mainly involved in drug metabolism is thiopurine S-methyltransferase (TPMT). An increased concentration of drug metabolites can cause adverse drug effects, such as myelosuppression and hepatotoxicity; therefore, assessing the activity of TPMT is essential both before and during treatment. TPMT genotyping result is not affected by previous thiopurine dose and currently is the primary component of TPMT activity and disease monitoring. Until now, more than 40 allelic variants of the TPMT gene have been reported, with most of them having an uncertain or no enzyme function. In this article, we report the first case of a novel TPMT allele, TPMT*45, that was identified in a Korean girl with CD whose findings suggested decreased TPMT activity. This newly observed variant is caused by a single nucleotide polymorphism resulting in nonsense mutation (c.676C>T, p.R226*) and the partial loss of amino acids in the TPMT protein. Initially, the patient began azathioprine at a standard dosage (1.5 mg/kg/day), and her laboratory results, including red blood cell (RBC) TPMT activity (6-methylmercaptopurine 2.68 nmol/mL/h and 6-methylmercaptopurine riboside 4.82 nmol/mL/h) along with thiopurine metabolite levels (6-thioguanine nucleotides 479.3 pmol/8×108 RBC), suggested an enzyme deficiency. The thiopurine dose was reduced to half (0.7 mg/kg/day), and the follow-up metabolite results as well as the associated inflammatory markers were continuously within reference ranges. Along with an improvement in the patient's subjective reports and clinical symptoms, the patient demonstrated a good treatment response to the adjusted dose. The results of our report illustrate the importance of TPMT genotyping and pharmacogenetic-based thiopurine dose adjustment. Further research should focus on the functional characterization and impact on this novel allele's treatment effect.

Down-Regulation of Serum High-Mobility Group Box 1 Protein in Patients with Pulmonary Tuberculosis and Nontuberculous Mycobacterial Lung Disease

BACKGROUND

Recently, increased levels of high-mobility group box 1 protein (HMGB1) have been identified in various inflammatory conditions and infections. However, no studies have evaluated the HMGB1 level in nontuberculous mycobacterial (NTM) lung disease, and compared it to mycobacterial lung disease.

METHODS

A total of 60 patients newly diagnosed with NTM lung disease, 44 culture-positive pulmonary tuberculosis (TB) patients, and 34 healthy controls, were included in this study. The serum HMGB1 concentrations were quantified using HMGB1 enzyme-linked immunosorbent assay kits.

RESULTS

Serum HMGB1 level in patients with pulmonary TB or NTM lung disease, was significantly lower than that of the healthy controls. In addition, the serum HMGB1 level in TB patients was significantly lower than patients with NTM lung disease. However, the levels in NTM patient subgroups did not differ according to the causative species, disease progression, and disease phenotype.

CONCLUSION

Although low levels of serum HMGB1 has the potential to be a marker of mycobacterial lung disease, these levels were unable to differentiate disease progression and disease phenotype in NTM lung diseases.

Optimal Use and Need for Therapeutic Drug Monitoring of Teicoplanin in Children: A Systematic Review

BACKGROUND

Teicoplanin is a glycopeptide antimicrobial that treats serious invasive infections caused by gram-positive bacteria, such as the methicillin-resistant Staphylococcus aureus. Despite some comparable advantages, there is no guideline or clinical recommendation for teicoplanin in the pediatric population, unlike vancomycin where abundant studies and the recently revised guideline on therapeutic drug level monitoring (TDM) exist.

METHODS

The systematic review was performed in accordance with the preferred reporting items for systematic reviews. Two authors (JSC and SHY) searched PubMed, Embase, and Cochrane Library databases using relevant terms independently.

RESULTS

Fourteen studies were finally included with a total of 1,380 patients. TDM was available in 2,739 samples collected in the nine studies. Dosing regimens varied widely, and eight studies used recommended dosing regimens. Timing for measuring TDM was mostly 72-96 hours or longer after the initiation of the first dose, which was expected to be a steady-state. The majority of studies had target trough levels of 10 µg/mL or above. Three studies reported that the clinical efficacy and treatment success rate of teicoplanin was 71.4%, 87.5%, and 88%. Adverse events associated with teicoplanin use were described in six studies with a focus on renal and/or hepatic impairment. Except for one study, no significant relation was noted between the incidence of adverse events and trough concentration.

CONCLUSION

Current evidence on teicoplanin trough levels in pediatric populations is insufficient due to heterogeneity. However, target trough levels with favorable clinical efficacy are achievable by recommended dosing regimen in the majority of patients.

Association of ATP7B mutation detection rate with biochemical characteristics in Korean patients with Wilson disease

Wilson disease (WD) is an autosomal recessive disorder caused by mutations in the ATP7B gene, yet many patients have either one mutation, or no mutation. We investigated whether the mutation detection rate is associated with any biochemical characteristics of WD. In a study of 71 patients, we used PCR-sequencing to screen for ATP7B mutations in 7 exons (exons 8, 10, 11, 14, 15, 16, and 18) covering 95% of known mutations in Korean patients with WD. We also investigated serum concentrations of various biochemical analytes. Data were analyzed by linear association test and one-way ANOVA. Based on the number of detected ATP7B mutations, a significant difference in serum ceruloplasmin concentration was found among the 3 groups (p <0.001). Serum ceruloplasmin concentration averaged 3.32 +/- 1.74, 10.8 +/- 5.50, and 14.9 +/- 3.88 mg/dl (mean +/- SD) in the 25, 20, and 26 patients with two, one, and no ATP7B mutations, respectively. We observed 82.9% and 16.7% of mutant allele frequency in WD patients with ceruloplasmin concentration <10 mg/dl and 10-20 mg/dl, respectively (p <0.001). Thus serum ceruloplasmin concentrations among WD patients differed according to the number of ATP7B mutations detected.

Comparative Analysis of Liquid Chromatography-Tandem Mass Spectrometry and Radioimmunoassay in Determining Plasma Aldosterone Concentration and Plasma Renin Activity for Primary Aldosteronism Screening

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) accurately measures plasma aldosterone concentration (PAC), but its correlation with radioimmunoassay (RIA), equivalent RIA levels, and optimal cutoff for PAC and aldosterone-to-renin ratio (ARR) in primary aldosteronism (PA) screening have not been determined in a Korean population. Our study of 127 patients who underwent diagnostic testing for PA showed that the LC-MS/MS and RIA methods have good correlation, with a mean bias of 29.3% for PAC. An LC-MS/MS PAC level of 11.7 ng/dL was equivalent to an RIA PAC level of 15 ng/dL. Receiver operating characteristic curve analysis showed that an LC-MS/MS PAC level of 10.3 ng/dL and LC-MS/MS ARR level of 20.0 provided sensitivity of 73.1% with a specificity of 57.3% and sensitivity of 92.3% with a specificity of 14.7%, respectively. When the LC-MS/MS method is used for PA screening, an adjustment of cutoff values is necessary.

A novel ATP7A gross deletion mutation in a Korean patient with Menkes disease

Menkes disease (MD, MIM 309400) is a fatal X-linked recessive disorder that is caused by mutations in the gene encoding ATP7A, a copper-transporting, P-type ATPase. Patients with MD are characterized by progressive hypotonia, seizures, failure to thrive, and death in early childhood. Two Korean patients were diagnosed with Menkes disease by clinical and biochemical findings. We found one missense mutation and one gross deletion in the ATP7A gene in the patients. The missense mutation in Patient 1, c.3943G>A (p.G1315R) in exon 20, was identified in a previous report. Patient 2 had a gross deletion of c.1544-?_2916+?, which was a novel mutation. The patients' mothers were shown to be carriers of the respective mutations. Prenatal DNA diagnosis in the family of Patient 2 was successfully performed, showing a male fetus with the wild-type genotype. The gross deletion is the first mutation to be identified in the ATP7A gene in Korean MD patients. We expect that our findings will be helpful in understanding the wide range of genetic variation in ATP7A in Korean MD patients.

Therapeutic Drug Level Monitoring of Teicoplanin in Korean Pediatric Patients with Normal versus Impaired Renal Function

BACKGROUND

Teicoplanin is used to treat serious gram-positive infections. Optimal teicoplanin trough levels are considered to be ≥ 10 μg/mL. Despite its wide use in various clinical settings, data on teicoplanin trough level in pediatric patients are limited. Therefore, the aim of this study was to investigate the therapeutic drug level monitoring of teicoplanin in Korean pediatric patients, including those with impaired renal function.

METHODS

A retrospective study was performed in pediatric patients (age ≤ 18 years old) who received teicoplanin from September 2014 to April 2018. The regimen included a loading dose of 10 mg/kg/dose at 12 hours' interval three times in a row, and a maintenance dose of 10 mg/kg/dose commenced at 24 hours of interval after the loading dose, with a maximum of 400 mg/dose, respectively. The first therapeutic drug levels were measured. Distribution and characteristics of trough levels in patients with decreased renal function and those with bacteremia were also assessed.

RESULTS

A total of 187 trough levels were collected from 143 patients. Hematologic and oncologic diseases were the most common underlying diseases (83.2%, n = 119). One hundred eighty trough levels were first measured, and their median value was 16.2 μg/mL (range, 2.3-100 μg/mL) and the median interval between initial teicoplanin injection and 1st trough level was 96.5 hours (range 47.6-179.3 hours). Lower steady-state levels were observed in younger age group (median, 13.5 vs. 18.0 μg/mL, P = 0.038). Median trough levels were higher in patients with decreased renal functions (P < 0.001). In addition, among eight with gram-positive bacteremia, seven of them had a favorable outcome.

CONCLUSION

This study provides additive information on trough level monitoring of teicoplanin in children with impaired renal function and treatment effect in patients with gram-positive bacteremia. Careful monitoring for steady state trough levels of teicoplanin is warranted.

Genetic polymorphisms and their association with methotrexate polyglutamates during maintenance treatment in Korean children and young adults with acute lymphoblastic leukemia

The aim of this study was to investigate the impact of genetic polymorphisms on methotrexate (MTX) metabolism in Korean children and young adults with acute lymphoblastic leukemia, specifically focusing on MTX polyglutamates (MTX-PGs) in erythrocytes, which have been rarely studied. Korean children and young adult patients undergoing maintenance therapy for acute lymphoblastic leukemia, who were receiving weekly oral MTX doses of 20 mg/m²/week, were prospectively included. We investigated erythrocyte MTX-PG (PG1 to PG5) levels, MTX-PG/MTX dose ratios, and 222 genetic polymorphisms spanning 78 genes and three intergenic areas related to MTX transport, folate cycle metabolism, purine/pyrimidine pathways, and non-pathway genes (including TPMT and NUDT15 genotypes) to explore their association with MTX metabolism. MTX-PG levels were associated with MTX dose (p < 0.05), and MTX-PG3 comprised the majority of the total MTX-PGs, with a median of 39.3 %. Various polymorphisms within the same gene demonstrated differing associations with each type of MTX-PG, underscoring the complexity of MTX pharmacogenetics. Among the polymorphisms examined, 14 across 13 genes showed significant associations with MTX-PG2-5 levels, even after adjusting for the false discovery rate (ABCC5, ATG16L1, CEP72, FSTL5, GMPS, HTR3A, IMPDH1, NT5C2, SLC28A3, SLCO1B3, SUCLA2, TPMT, and TYMS). This study enhances our understanding of genetic polymorphisms in MTX metabolism and therapeutic monitoring for MTX maintenance, promoting personalized medicine in acute lymphoblastic leukemia patients.

Clinical Pharmacogenetic Testing and Application: 2024 Updated Guidelines by the Korean Society for Laboratory Medicine

In the era of precision medicine, pharmacogenetics has substantial potential for addressing inter-individual variability in drug responses. Although pharmacogenetics has been a research focus for many years, resulting in the establishment of several formal guidelines, its clinical implementation remains limited to several gene-drug combinations in most countries, including Korea. The main causes of delayed implementation are technical challenges in genotyping and knowledge gaps among healthcare providers; therefore, clinical laboratories play a critical role in the timely implementation of pharmacogenetics. This paper presents an update of the Clinical Pharmacogenetic Testing and Application guidelines issued by the Korean Society for Laboratory Medicine and aims to provide the necessary information for clinical laboratories planning to implement or expand their pharmacogenetic testing. Current knowledge regarding nomenclature, gene-drug relationships, genotyping technologies, testing strategies, methods for clinically relevant information delivery, QC, and reimbursements has been curated and described in this guideline.

Identification of PRODH mutations in Korean neonates with type I hyperprolinemia

BACKGROUND

Hyperprolinemia is a rare inherited metabolic disorder characterized by a high proline level in blood and/or urine and various neuropsychiatric symptoms. Type I hyperprolinemia is caused by a proline oxidase deficiency, which is encoded by the PRODH gene on chromosome 22q11. Herein, we present a study of Korean patients with type I hyperprolinemia who were diagnosed during newborn screening by tandem mass spectrometry and confirmed by molecular analysis.

METHODS

Four neonates were referred to our hospital for workup of high proline levels in newborn screening test. We analyzed the biochemical findings and the PRODH gene was amplified by long-range PCR to confirm molecular genetic abnormalities.

RESULTS

All patients had high plasma proline levels, ranging from 742 to 1192 μmol/L (reference range, 77.4 - 244.6 μmol/L). In molecular analysis, 4 disease-associated mutant alleles were identified: c.1414G>A (p.A472T), c.1279G>A (p.V427M), c.1357C>T (p.R453C) and c.1562A>G (p.Q521R). All mutations were missense and c.1279G>A included the majority of mutant alleles. No relationships between type of mutation and clinical outcomes were observed.

CONCLUSION

We found that distinct molecular alterations of the PRODH gene result in abnormal proline levels. Newborn screening and molecular analysis are necessary to identify patients before clinical expression of metabolic disease.

Multiplex ligation-dependent probe amplification assay for diagnosis of congenital adrenal hyperplasia

Mutations in the CYP21A2 gene encoding the 21-hydroxylase enzyme account for >90% of congenital adrenal hyperplasia (CAH) cases. Approximately 20% of mutant alleles carrying large deletion/duplication have also been reported. Herein, we describe the use of the multiplex ligation-dependent probe amplification (MLPA) method for convenient and rapid detection of deletions/duplications in the CYP21A2 gene. We used MLPA to analyze the gene dose of CYP21A2 MLPA in 13 Korean patients who previously underwent direct sequencing for the molecular diagnosis of CAH. The MLPA assays identified 5 patients with CYP21A2 deletions; all 5 patients carried a single mutant allele peak in sequence analysis. These results demonstrate the diagnostic usefulness of MLPA to detect CYP21A2 deletions/duplications for diagnosis of CAH.

A novel PHKA2 gross deletion mutation in a Korean patient with X-linked liver glycogenosis type I

X-linked liver glycogenosis (XLG) is caused by a mutation in the PHKA2 gene which encodes the alpha subunit of phosphorylase kinase (PHK). Although XLG is not a rare disease, there have been no reports of PHKA2 mutations in Koreans. A 5-year-old boy presented with easy fatigability and hepatomegaly. Liver enzymes were increased and liver histology revealed deposition of glycogen. The PHK activity was markedly decreased compared to control. No amplification was observed at exon 8 of the PHKA2 gene, as a result of the deletion of exon 8. Sequence analysis revealed a hemizygous deletion in the region of exon 8 (c.717+781_864+225del1626). The patient was diagnosed as having XLG I. To the best of our knowledge, this is the first report of XLG I in Koreans.

SLC22A5 mutations in a patient with systemic primary carnitine deficiency: the first Korean case confirmed by biochemical and molecular investigation

Systemic primary carnitine deficiency (CDSP) is a rare autosomal recessive disorder that presents episodic periods of hypoketotic hypoglycemia. The main symptoms of CDSP are skeletal and cardiac myopathy. CDSP is caused by a defect in plasma membrane uptake of carnitine, ultimately caused by the SLC22A5 gene. We report the case of a Korean patient with CDSP. He had an abnormal free carnitine level of 5.56 μmol/L (reference range, RR 10.4~87.1 μmol/L) and a palmitoylcarnitine level of 0.27 μmol/L (RR 0.5~9.7 μmol/L) in a newborn screening test. The patient showed an ammonia level of 129.4 ug/dL (RR, 25~65 ug/dL), a lactate level of 4.5 mmol/L (RR, 0.5-2.2 mmol/L), and a free carnitine level of 10.3 μmol/L (RR, 36-74 μmol/L) in blood. After PCR-sequencing analysis of the SLC22A5 gene, the patient was found to be a compound heterozygote for c.506G>A (p.R169Q) and c.1400C>G (p.S467C) mutations. These missense mutations are reported previously. The patient was started on L-carnitine supplement after CDSP diagnosis. The patient was treated with L-carnitine to reach a normal free carnitine level and has remained asymptomatic up to the current age of 21 months. The plasma free carnitine level normalized to 66.6 μmol/L at 4 weeks after treatment. To the best of our knowledge, this is the first report of a CDSP patient confirmed by molecular genetic investigation.

Two novel FAH gene mutations in a patient with hereditary tyrosinemia type I

BACKGROUND

Hereditary tyrosinemia type I (HT I) is a severe inborn metabolic disorder affecting the tyrosine degradation pathway. Most untreated patients die within the first two years of life. HT I results from fumarylacetoacetate hydrolase (FAH) deficiency caused by mutations in the FAH gene. The diagnosis of HT I is confirmed by measuring FAH enzyme activity in cultured fibroblasts or liver tissue and/or detecting disease-causing mutations in the FAH gene.

METHODS

A female neonate was referred to our hospital for further evaluation of an abnormal newborn screening test that showed elevated tyrosine levels. We analyzed amino acids and organic acids in the patient's blood and urine. To identify the genetic abnormality, all the coding exons and flanking introns of the FAH gene were analyzed via PCR.

RESULTS

A repeat newborn screening test and plasma amino acid analysis revealed increased tyrosine levels in the patient. Urine organic acid analysis showed increased urinary excretion of 4-hydroxyphenyllactate, 4-hydroxyphenylpyruvate, and succinylacetone. Sequence analysis of the FAH gene identified two novel variations (c.536A>G (p.Gln179Arg) and c.913+5G>A) that had not been previously reported and that were not found in 170 healthy controls.

CONCLUSIONS

HT I was confirmed in this patient by molecular genetic analysis of the FAH gene, with highly suggestive biochemical findings. The novel sequence variations detected in the present study should be considered disease-causing mutations by in silico analysis. In the Korean population, this is the first described case of HT I caused by a point mutation in the FAH gene.