Iron Deficiency Anemia in Infancy: Long-Lasting Effects on Auditory and Visual System Functioning

Abstract

Evoked potentials provide noninvasive measures of nerve transmission and CNS functioning. Auditory brainstem responses (ABR) and visual evoked potentials (VEP) show dramatic changes in infancy, largely as a result of progressive myelination. Because iron is required for normal myelination, pathway transmission in these sensory systems might be affected by early iron deficiency. We previously reported evidence to that effect: infants with iron-deficiency anemia (IDA) had slower transmission through the auditory brainstem pathway, uncorrected by iron therapy. To determine long-term effects, ABR and/or VEP of healthy Chilean children who were treated for IDA or were nonanemic in infancy were compared at approximately 4 y of age. Absolute latencies for all ABR waves and interpeak latencies (except I-III interval) were significantly longer in former IDA children. Longer latency was also observed for the P100 wave on VEP. The magnitude of differences was large-about 1 SD. These findings, with differences in latencies but not amplitudes, further support the hypothesis that IDA in infancy alters myelination and provide evidence that effects on transmission through the auditory and visual systems can be long lasting. Subtle changes in sensory pathway transmission might be an underlying mechanism for the derailment of other developmental aspects in early IDA. Neurophysiologic methodologies are noninvasive approaches that can provide information about the functional integration of the CNS. For example, dramatic decreases in latencies in auditory and visual evoked potentials in infancy are often used to index the overall intactness and maturation of the CNS. Progressively shorter latencies until adult levels are achieved are thought to reflect the increasing speed of transmission through sensory pathways, resulting in large part from increased myelination of the auditory and optic nerves and at the intracerebral level (1-5).ABR represent the progressive activation of different levels of the auditory pathway: wave I is generated peripherally in the auditory nerve, wave III reflects the firing of axons exiting the cochlear nuclear complex, and wave V reflects an action potential generated by axons from the lateral lemniscus (6, 7). We recently reported the use of ABR to determine the effects of early IDA on the functional development of the auditory system (8). Six-month-old Chilean infants with IDA tended to show longer latencies than controls, indicating slower transmission through the brainstem portion of the auditory pathway. Differences became pronounced at 12 and 18 mo, despite iron therapy. Because iron is required for the functioning of several neurotransmission systems, myelination, and neuronal metabolic activity, different processes may relate to these lasting ABR abnormalities. However, the findings of differences in latency but not amplitude and more effects on the central (versus peripheral) portion of the auditory pathway appeared to be strong support for the hypothesis that impaired myelination was the explana...

Iron Status and Neurobehavioral Development of Premature Infants

“…These authors suggested that altered myelination was the most likely explanation for their findings. 39,40 As the definition of abnormality of reflex in our study included latency, one possible explanation for our findings is impaired myelination in the low-iron group. However, in addition to latency, our definition also included the level of excitation.…”

Maternal anaemia in West and Central Africa: time for urgent action

“…Infants born to anaemic mothers experience more growth faltering and are developmentally delayed in hand-eye movement and overall cognitive quotient (47) . They also are at higher risk for intra-uterine fetal death (44) , long-lasting adverse effects on auditory and visual system functioning (49) and poor behavioural outcomes, which are only partially irreversible unless corrected early (50,51) .…”

Effectiveness of iron repletion in the diet for the optic nerve development of anaemic rats

“…40,41 Iron deficiency affects the normal myelination and the pathway transmission in the sensory systems. 11,12 Trace elements deficiency, undernourishment, and exposure to drugs of abuse or alcohol induced ultrastructural changes in the ON, cornea, and retina. 25,26,29,[31][32][33][34][35][42][43][44][45][46][47][48][49][50][51][52][53] Figure 2 Mean density (a) and total number (b) of myelinated and unmyelinated fibres of the optic nerve in the control, anaemic, and recovered rats at postnatal day 32.…”

“…6,13 Iron-deficient children were reported to have longer auditory brainstem response and visual-evoked potential latencies attributed to hypomyelination. 11 The neural functioning and behavioural consequences on brain iron deficits are not limited to infants. 6,13 There are growing evidences that iron deficiency in early development affected brain myelination, 14,22,58 and some of them include a general decrease of its content and a differential composition of myelin.…”

“…Moreover, iron deficiency in humans is reportedly associated with a decrease in auditory and visually evoked potentials attributed to hypomyelination. 11 Magnetic resonance imaging in human infants also indicated that altered iron status is associated with hypomyelination. 12 The role of iron in myelination and oligodendrocyte biology has been studied for several decades.…”