Non-alcoholic fatty liver disease (NAFLD) is one of the most common causes of chronic liver disease worldwide. It is not known why only some obese subjects develop NAFLD. In recent years, a growing body of evidence showed a crucial role of autophagy in in the regulation of liver fat storage. The purpose of this study is to determine whether autophagy pathway-related genetic polymorphisms affect NAFLD.

The investigators will perform a prospective comparison of the genotype distribution of autophagy pathway-related genetic polymorphisms between those with and without NAFLD in a cohort of obese children and adolescents.

[Subjects] Obesity is defined as the BMI value > 95 percentile by different age- and gender groups according to the standards of the Department of Health in Taiwan.

[Data collection] The following data were obtained for each subject: age, gender, BMI, waist and hip circumference. The investigators will measure total serum bilirubin, alanine aminotransferase, aspartate aminotransferase, γ-glutamyltransferase fasting glucose, triglyceride, total cholesterol, and high-density lipoprotein cholesterol, insulin, glucose, and adiponectin.

[Liver ultrasonography] All participants will receive an ultrasonographic study of the liver. NAFLD is defined as the presence of an ultrasonographic pattern consistent with the following criteria: liver-kidney echo discrepancy, attenuated echo penetration and visibility of diaphragm, and obscure hepatic vessel structures.

[Genotyping] Genomic DNA will be extracted from 3 cc venous blood from each participant. After extraction, the genomic DNA will be immediately stored at -80°C. The TaqMan genotyping assays will be performed for selected SNPs genotyping on ABI 7300 Real-Time PCR System (Applied Biosystems).

[Sample size] Sample size was estimated by Epi InfoTM 7 (CDC, USA) program. Because there was no previous data regarding to the effect of autophagy related gene on NAFLD, the investigators estimate the odds ratio to vary between 60-80%. The investigators used a confidence level of 95%, power of 80%, the ratio of controls to NAFLD cases of 25%, percent of controls exposed of 25-35%, the samples size required would be a total of 291-872 subjects.

Inclusion criteria:

• Age 6-18 years old
• Obesity definition: BMI > 95% according to the age- and gender-specific standard by National Health Institute in Taiwan
• Willing to give written informed consent

Exclusion criteria:

• Alcohol consumption
• Chronic liver diseases, including hepatitis B, hepatitis C, Wilson disease and autoimmune hepatitis
• Major systemic diseases, including cardiopulmonary disease, renal failure, cancer, and psychotic disorder

Obese Taiwanese children and adolescents