Declines in IQ Identified in Children With Type 1 Diabetes

Becky McCall

December 15, 2014

The first study to follow intelligence quotient (IQ) in type 1 diabetes patients from diagnosis in childhood into young adulthood has shown that the condition can affect some aspects of IQ.

The findings, published online December 8 in Diabetes Care, show evidence of a selective impact of specific disease risk factors on IQ.

For example, diagnosis with type 1 diabetes at an earlier age was associated with a decline in visuospatial [performance] aspects of IQ, while hypoglycemic seizures, but not hyperglycemia, appear to affect verbal IQ [word knowledge and abstract verbal conceptual reasoning]," lead investigator Dr Ashleigh Lin (Telethon Kids Institute, University of Western Australia, Perth) told Medscape Medical News.

Although these associations are not novel, access to IQ scores from diagnosis through 12 years of follow-up into young adulthood provides "particularly compelling evidence that the timing of diabetes onset and exposure to serious hypoglycemia are significant factors in the cognitive sequelae of type 1 diabetes," the researchers say.

"We know that, years after diagnosis, young people with type 1 diabetes show lower IQ, particularly if they are diagnosed early — age 5 or younger — or have a history of hypoglycemic seizures," explained Dr Lin.

"Academic progress of children identified as at risk should be monitored, and educational supports provided if necessary," she and her colleagues advise.

Unique Study Design

Dr Lin and colleagues prospectively followed 95 patients admitted at diagnosis of type 1 diabetes to the Royal Children's Hospital, Melbourne, Australia, between 1990 and 1992 and compared them with 67 healthy controls.

Dr Lin remarked that their study was unique in design because it was the first to follow children periodically from time of diagnosis, as well as following healthy participants recruited at the same time as those with diabetes.

"Being able to follow up both groups of children into young adulthood 12 years later is an achievement, especially since the majority of the cohort had transitioned into adult diabetes services and were no longer managed at the Royal Children's Hospital," she noted.

Measures of IQ included the Wechsler Preschool and Primary Scale of Intelligence—Revised, Wechsler Intelligence Scale for Children—Revised, and Wechsler Abbreviated Scale of Intelligence, providing scores for full-scale IQ, verbal IQ, and performance IQ.

Data on metabolic control history were also prospectively collected.

At the final follow-up, those with type 1 diabetes and the healthy controls had a mean age of 21.3 years.

Lower Verbal and Full-Scale IQ

Of greatest significance were the findings that young people with type 1 diabetes exhibited lower verbal IQ and full-scale IQ (full-scale IQ is the composite IQ measure across both verbal and performance domains) in the 12 years following diagnosis, as compared with healthy participants.

Overall in type 1 diabetes, the mean change in verbal IQ over 12 years was -7.84 and in full-scale IQ was -6.12. In healthy participants the mean change in verbal IQ over the same time period was -6.46 and in full-scale IQ was -5.58.

The researchers note that the reason some decline in IQ scores was evident in both type 1 diabetes patients and healthy controls probably reflects, in part, "the use of a more recently normed [IQ] test at follow-up."

For those with early-onset diabetes, the declines were even greater, with a mean change in verbal IQ over 12 years of -10.52 and in full-scale IQ of -11.38. Similarly, in patients with a history of hypoglycemia, the mean changes were -11.02 in verbal IQ and -7.10 in full-scale IQ.

Thenegative impact of severe hypoglycemia on language-skills development has been reported by other researchers, but the reasons for this association remain unknown, Dr Lin pointed out.

"We know that language skills are sensitive to educational opportunity. Children who are prone to hypoglycemia may be less efficient learners in the classroom because low blood glucose levels impair concentration in the school setting, having a cumulative negative impact on language development," she speculated.

"We also know that frontal-temporal regions of the brain require high levels of glucose, so glucose deprivation may impair skills such as semantic memory, which underpin optimal language development."

More Frequent Assessment of IQ Needed in Children With Diabetes

However, in contrast to other groups that have shown that poor metabolic control is associated with lowered cognitive ability, Dr Lin and colleagues were unable to find a significant association between HbA1c measurements and changes in IQ.

"It is very difficult to obtain accurate records of lifetime HbA1c, especially if the young person has transitioned to adult care or changed pediatric hospitals. This may have affected the results, and we think it would be premature to dismiss the potential impact of poor metabolic control on brain structure and function," Dr Lin said.

She added that they did not collect data on academic performance throughout the whole schooling for these children, either, although fewer participants with type 1 diabetes than healthy participants completed the preuniversity year of schooling in Australia, "providing some external validation of our findings."

Nor did the study provide information on the timing or trajectory of changes in IQ, which limits the ability to implement specific interventions during the highest-risk periods.

Likewise, the impact of type 1 diabetes on central nervous system (CNS) structure and function remains unknown.

"More frequent assessment of youth with type 1 diabetes will help clarify the timing and trajectory of functional and structural brain changes to optimize intervention," the researchers observe.

In conclusion, Dr Lin said that the findings were important because they may help identify specific young patients who are most at risk of particular deficits. "For example, a person with early-onset diabetes might benefit from some extra practice with visuospatial tasks," she suggested.

Dr Lin has declared she has no relevant financial relationships. Disclosures for the coauthors are listed in the article.

Diabetes Care. Published online December 8, 2014. Abstract

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