Neurobehavioral symptoms play a central and often underrecognized role in primary mitochondrial disorders, including thymidine kinase 2 deficiency (TK2d), and in some cases may affect quality of life as much as physical complications, according to findings from a single-center multidisciplinary program published recently in Genetics in Medicine Open.
“While acute crisis management remains central to PMD [primary mitochondrial disorder] care, ongoing attention to neurobehavioral health is essential for improving daily functioning and family well-being,” explained the authors of this research.
Primary mitochondrial disorders are genetically diverse diseases that affect multiple organ systems, particularly the brain. Patients frequently experience seizures, lactic acidosis, stroke-like episodes and developmental regression, along with chronic challenges such as feeding difficulties, breathing problems and sensory impairments. Although intellectual disability is widely recognized, less is known about the full range of behavioral and emotional effects.
To better understand these patterns, researchers reviewed several patient cases evaluated through a multidisciplinary program that included specialists in genetics, psychology and developmental care. Assessments combined clinical observations with standardized cognitive and behavioral testing to build detailed neurobehavioral profiles.
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One case involved a 10-year-old boy with pyruvate dehydrogenase deficiency who showed below-average cognitive abilities but relatively stronger verbal reasoning. His daily life was heavily affected by impulsivity, anxiety and emotional instability. Another case described a 7-year-old boy with mitochondrial encephalopathy who had severe developmental delays and persistent irritability, along with sleep disruption that required behavioral therapy and medication.
More severe manifestations were also observed. A 6-year-old girl with a mitochondrial fission disorder exhibited profound cognitive impairment and self-injurious behaviors, requiring intensive safety planning. In contrast, an 8-year-old girl with TANGO2 deficiency showed strong social engagement despite significant developmental challenges, highlighting the variability seen across these conditions.
Across all cases, common features included intellectual disability, anxiety, irritability and difficulty with adaptive functioning. Importantly, these behavioral symptoms often appeared to be part of the underlying disease process rather than a response to acute metabolic episodes. This distinction matters for patients with TK2d and similar disorders, as it supports earlier and more targeted interventions.
For patients and families, these findings emphasize that care should extend beyond managing medical crises. Addressing behavioral and emotional health through coordinated, multidisciplinary support can help improve daily functioning, reduce stress on caregivers and enhance overall well-being.
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