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Developmental Delays

The range of cognitive development that occurs in patients with mitochondrial disease is as broad as possible, and demonstrates how difficult it is to prognosticate about a patient's long-term outcome. Some patients exhibit delays from birth and have evidence of prenatal onset disease, demonstrating seizures at birth or congenital hypotonia. Others may display no apparent cognitive issues for decades, if at all.

Developmental delays and learning disorders are common with no particular predisposition toward a specific pattern of disability. However, because patients are at risk, close developmental monitoring is necessary and important to maximize a child's educational experience at school. Likewise, neuropsychological testing in adults can identify deficits and areas of concern, permitting counseling and a plan for rehabilitation that targets relative strengths and options for compensation.

On the one hand, testing a patient at his/her best can provide a more accurate assessment of abilities and challenges. However, a patient's level of ability may fluctuate a lot over the day or during the week depending on his/her level of fatigue. Many patients have more energy in the morning and may experience shorter bursts during the rest of the day; as the week progresses, fatigue becomes a bigger issue. As fatigue increases, the capacity to learn or concentrate on work diminishes. Because fatigue is not only an issue at home but also at school or in the work-place, a thorough developmental (or neuropsychological) evaluation should assess the child under optimal working conditions (to assess full capabilities) but also at a time when s/he is fatigued. Developing an educational (or working) plan for both scenarios is realistic and practical.

It is common for parents or caregivers to take measures that not only keep a child safe but also comfortable. For example, when a child is overly fatigued or not feeling well, the impulse may be to keep the child at home until s/he is feeling better. While this approach is understandable, it also keeps teachers and therapists from observing the child under these circumstances and understanding the full range of what s/he has to deal with. This can be an unfortunate situation and over the long term may interfere with the educational planning process. Consideration should be given to allow the child to participate in school or activities to their best of his/her ability, even when s/he is not having a "good day" (as long as safety is not a concern). The more knowledgeable the people in the child's day-to-day life, the more likely they can act as allies in his/her care.

The progressive nature of mitochondrial disease also means that the recommendations generated in a patient evaluation may have a time-limited applicability. A follow-up assessment during the (school) year might be warranted, especially if the patient's status has changed, and some assessment is certainly needed in advance of any discussion in which educational planning is to occur. Therefore, more often than not, recommendations should be considered tentative with a need for follow-up.

Permanent regression can also occur as part of the disease process. More common however is transient regression, occurring periods of physiologic stress such as infections or following surgery; recovery to baseline may take days or weeks depending in part upon the severity and duration of the stressor. With severe or prolonged stressors, such as recurring significant infections, recovery can be even more prolonged and perhaps not complete so that a new, lower baseline is established. Such a change is not usually predicable ahead of time.


  1. Regular monitoring of development or functioning.
  2. Obtain feedback from parents, teachers, therapists, and other special education and activity leaders. For adult patients, this input can come from relatives, therapy or community workers, colleagues at work, or work representatives (when possible).


  1. Neuropsychological testing. If formal testing is required, recommend that it occur over two or more sessions in order to assess the patient under different situations. Follow-up evaluations and discussions should be part of any recommendations since the patient's status can change over time.
  2. Permit teachers, therapist, and other providers the opportunity to observe and interact with the patient on "good days" and "bad days" to ensure a more appropriate educational or working plan.
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