Elevated aminotransferase as a presenting finding in a patient with occult muscle disease

Serum glutamate dehydrogenase activity enables sensitive and specific diagnosis of hepatocellular injury in humans

Serum activities of alanine- and aspartate aminotransferases (ALT and AST) are considered the "gold standard" biomarkers of hepatocyte injury in clinical practice and drug development. However, due to the expression of ALT and AST in myocytes, the diagnosis of hepatocellular injury in patients with underlying muscle diseases, including drug-induced muscle injury, is severely limited. Thus, we proposed glutamate dehydrogenase (GLDH) as a liver-specific alternative to serum ALT and AST. In fact, our exploratory studies showed that GLDH has comparable performance to ALT for detecting hepatocyte injury without interference from concomitant muscle injury. Here, we report the results of studies confirming the reference intervals in a healthy human population and the sensitivity and specificity of GLDH for the detection of hepatocyte injury in human subjects. In human subjects, we could not perform liver biopsies due to ethical reasons; we also confirmed the relationship of GLDH and histopathologic lesions using 32 model toxicants in rats. Furthermore, we have shown that injury to tissues that are known to express appreciable levels of GLDH does not affect serum GLDH measurements, indicating excellent liver specificity of serum GLDH. Finally, we observed faster elimination of GLDH than ALT in humans, indicating that decreasing GLDH values could be considered an early sign of recovery. This study provides comprehensive evidence of excellent sensitivity and liver specificity of GLDH for diagnosis of hepatocellular injury, including evaluation of reference intervals, which is essential for the interpretation of serum GLDH in human subjects.

Serum glutamate dehydrogenase activity enables early detection of liver injury in subjects with underlying muscle impairments

Serum activities of alanine and aspartate aminotransferases (ALT and AST) are used as gold standard biomarkers for the diagnosis of hepatocellular injury. Since ALT and AST lack liver specificity, the diagnosis of the onset of hepatocellular injury in patients with underlying muscle impairments is severely limited. Thus, we evaluated the potential of glutamate dehydrogenase (GLDH) as a liver specific alternative biomarker of hepatocellular injury. In our study, serum GLDH in subjects with Duchene muscular dystrophy (DMD) was equivalent to serum GLDH in age matched healthy subjects, while serum ALT was increased 20-fold in DMD subjects. Furthermore, serum GLDH in 131 subjects with variety of muscle impairments was similar to serum GLDH of healthy subjects while serum ALT corelated with serum creatine kinase, a widely accepted biomarker of muscle impairment. In addition, significant elevations of ALT, AST, and CK were observed in a case of a patient with rhabdomyolysis, while serum GLDH stayed within the normal range until the onset of hypoxia-induced liver injury. In a mouse model of DMD (DMD^mdx), serum GLDH but not serum ALT clearly correlated with the degree of acetaminophen-induced liver injury. Taken together, our data support the utility of serum GLDH as a liver-specific biomarker of liver injury that has a potential to improve diagnosis of hepatocellular injury in patients with underlying muscle impairments. In drug development, GLDH may have utility as a biomarker of drug induced liver injury in clinical trials of new therapies to treat muscle diseases such as DMD.

Serum Enzyme Profiles Differentiate Five Types of Muscular Dystrophy

Background. Differentiation among types of muscular dystrophy (MD) has remained challenging. In this retrospective study, we sought to develop a methodology for differentiation of MD types using analysis of serum enzyme profiles. Methods. The serum levels of enzymes from 232 patients, including 120 with DMD, 36 with BMD, 36 with FSHD, 46 with LGMD, and 11 with EDMD, were evaluated. Results. The characteristic profiles of serum enzymes facilitated differentiation of these five types of MD. DMD was characterized by simultaneous elevation of ALT, AST, LDH, and ALP; BMD and LGMD were characterized by elevation of ALT, AST, and LDH; and FSHD and EDMD were characterized by a lack of abnormal serum enzyme levels. We further developed discriminant functions to distinguish BMD and LGMD. For LGMD, LGMD2B patients had significantly higher ALP levels than non-LGMD2B patients (98 ± 59 U/L versus 45 ± 9 U/L, resp., p < 0.05). Conclusions. Our approach enabled the determination of MD subtypes using serum enzyme profiles prior to genetic testing, which will increase the chance a mutation will be found in the first gene analyzed.

Incidental raised transaminases: a clue to muscle disease

Twenty-one patients with incidental hypertransaminasaemia who were eventually diagnosed as muscular dystrophy are described. There were two females and 19 males aged between 2 and 11 years [mean (SD) 6.7 (3.4) y]. Serum alanine and aspartate transaminase levels were between 73 and 595 IU/L (30-35) and 68 and 550 IU/L (30-35), respectively. Muscle disease was suspected when creatine phosphokinase levels were elevated and confirmed in each patient by muscle biopsy. The time interval between incidental hypertransaminasemia and the diagnosis of muscle disease was between 3 and 12 months. Eleven patients were diagnosed as Becker's muscle dystrophy, eight as Duchenne muscle dystrophy and two had sarcoglycanopathy. Long-term elevation of transaminase levels might be a sign of occult muscle disease. Invasive tests such as liver biopsy should not be performed in patients with unexplained hypertransaminasaemia without first determining creatinine phosphokinase levels.

Aminotransferases and muscular diseases: a disregarded lesson. Case reports and review of the literature

The aim of this study was to call the attention to the often disregarded message that hypertransaminasemia may be a marker of both liver and muscle diseases by presenting personal case reports and a systematic literature review. Three male children (mean age 5.7 years) were inappropriately addressed, during the last 12 months, to our paediatric liver unit for diagnostic work-up of a chronic hypertransaminasemia of unknown origin. In one of them, a liver biopsy had already been performed. On admission, physical examination, evaluation of serum levels of creatine kinase, and dystrophin genetic testing finally led to a diagnosis of muscular dystrophy. One hundred fourteen similar cases, 21 with unnecessary liver biopsy, were found by Medline search. Expensive and invasive tests planned to investigate liver diseases should be postponed until alternative sources of increased serum aminotransferases, primarily myopathic injury, have been excluded.

The hospitalized patient with abnormal liver function tests

Evaluation of abnormal liver function tests (LFTs) in the hospitalized patient is typically more urgent than the outpatient setting. This process is best organized into four steps. The first step is to determine whether the abnormal LFTs are associated with the illness resulting in the admission to the hospital or preceded the present illness. The second is to determine the etiology of the underlying liver disease. The third step is to evaluate the severity of the liver dysfunction and determine if acute liver failure (ALF) or acute decompensation of chronic liver failure is present. The final step is to look for the presence of associated complications-either those of ALF or chronic liver failure as appropriate.

The asymptomatic outpatient with abnormal liver function tests

Traditionally, the constellation of biochemistry tests including liver enzymes, total bilirubin, and hepatic synthetic measures (prothrombin time (PT) and serum albumin level) are referred to as liver function tests (LFTs). Abnormal LFTs can be encountered during primary health care visits, routine blood donation, and insurance screening. A reported 1% to 4% of asymptomatic patients exhibit abnormal LFTs, leading to a sizeable number of annual consultations to a gastroenterology and/or hepatology practice. A cost-effective and systematic approach is essential to the interpretation of abnormal LFTs. A review of pattern of abnormal LFTs, detailed medical history, and a comprehensive physical examination help establish a foundation for further individualized testing. Further investigation often involves biochemical testing for disease-specific markers, radiographic imaging, and even consideration of a liver biopsy. In the following account, markers of hepatic injury are reviewed followed by a discussion on an approach to various patterns of abnormal LFTs in an asymptomatic patient.

Fidelity of gamma-glutamyl transferase (GGT) in differentiating skeletal muscle from liver damage

This study tested the hypothesis that gamma-glutamyl transferase (GGT) can be used as a reliable biomarker to distinguish skeletal muscle from liver damage. Twenty-eight Duchenne muscular dystrophy subjects with proven dystrophin gene mutations were enrolled. Included were 14 ambulatory and 14 nonambulatory patients with approximately half of each cohort taking corticosteroids. Twenty normal males served as controls. Initial blood samples for serum GGT and creatine kinase were taken between 8AM and 9AM and redrawn 8 hours later to test for variability. Between blood draws, subjects resumed normal activities in a play environment or could leave the clinic. Not a single duchenne muscular dystrophy patient showed a GGT outside the control range at any time point, while creatine kinase levels were 14 to 200 times normal. Validation of this finding is essential for management of patients with muscle disorders exposed to potentially hepatotoxic drugs for clinical management or monitoring subjects participating in clinical trials.