The Relationship between Cadmium and Tyrosine Hydroxylase Activity in Patients with Attention Deficit Hyperactivity Disorder (ADHD)

Abstract

Background: Attention Deficit Hyperactivity Disorder (ADHD) is a common neurodevelopmental disease characterized by inattention, hyperactivity, and impulsiveness. Dopamine deficiency is considered one of the key neurochemical underpinnings of ADHD. Tyrosine Hydroxylase (TH), the rate-limiting enzyme in the production of dopamine and other catecholamines. It has been increasingly studied for its potential role in ADHD. Future insights into TH regulation and its modulation may offer novel therapeutic strategies for affected children and adolescents. This study aimed to assess TH activity in individuals with ADHD and explore its relationship with cadmium (Cd) levels, comparing findings with those of healthy controls.

Methods: The current study was designed as a case-control study, involving 90 healthy control subjects and ADHD patients, aged between 4 and 18 years.  The patients were categorized into two groups: the first group included 60 patients with ADHD, and the second group represented the control group, which comprised 30 volunteers without any ADHD. The TH activity was measured using the ELISA technique. Additionally, the concentration of selected cadmium was determined using Atomic Absorption Spectroscopy (AAS).

Results: TH levels showed greater variability in ADHD patients but were not significantly different from controls. A significant negative correlation was found between TH and cadmium (r = –0.230, p = 0.029).  Multiple linear regression confirmed cadmium levels and treatment type as significant predictors of TH activity.

Conclusions: Cadmium exposure had a negative influence on tyrosine hydroxylase activity in patients with ADHD, suggesting an environmental impact on dopamine synthesis.