Learning disabilities in not unusual in children. From five to 15 percent of children and teens have overall normal or high levels of intelligence but deal with difficulties with verbal fluency, word decoding, spelling, writing, number sense, or mathematical reasoning. These handicaps don't mean that the child is in any way "retarded". They simply mean that there are certain academic skills that are difficult for them to achieve.
Researchers believe that when people who have learning disabilities as children develop dementia as adults, they tend to not to have typical cases of Alzheimer's disease. Instead, they are up to 128 times more likely to be diagnosed with:
- Younger-onset Alzheimer's disease, symptoms beginning before the age of 65.
- Logopenic primary progressive aphasia, a disease that causes loss of language before loss of memory or reasoning skills.
- Posterior cortical atrophy, a degenerative disease that attacks the back of the brain and causes difficulties with spelling, calculation, visual processing, and spatial perception.
- Dysexecutive-type Alzheimer's disease, a form of dementia that leaves memory intact but interferes with reasoning (at least at first).
People who have learning disabilities have higher odds of being diagnosed with frontotemporal lobar dementia in both of its common forms, the kind that affects speech first and the kind that causes loss of control over behavior first. These people are also more likely to be left-handed, male, and college graduates than people who develop Alzheimer's disease.
Some researchers interpret these findings as evidence for a kind of "brain vulnerability" in childhood learning disabilities and dementia later in life. The same parts of the brain are affected in childhood and late in adulthood. Usually, less of the brain is affected in atypical dementia than in Alzheimer's disease. But does this mean that if you have a learning disability in school you will develop dementia as a result?
- Left-handed people seem to be slightly (but significantly) at greater risk for childhood learning disabilities and for frontotemporal dementia.
- People who are diagnosed with dyslexia as children are at measurably greater risk for a form of dementia known as primary progressive aphasia, but only for a form of the condition known as the logopenic variant. This form of dementia makes it difficult to find words. Speech is usually slow. Initially, problems with language are the only symptoms of the disease.
- Genes that increase the likelihood of dyslexia also increase the likelihood of a form of primary progressive aphasia.
But being "more" susceptible to logopenic primary progressive aphasia doesn't mean you are likely to get the disease. About one person in 3500 is ever diagnosed with the condition. About 10 percent of these one in 3500 cases are matched with childhood dyslexia. If that is twice the expect number of matches, that still means that your risk only goes up to about one in 1750.
People with learning disabilities are at greater risk of developing dementia. But that risk is not very high, except when the learning disability is Down syndrome. Nearly everyone who has Down syndrome develops Alzheimer's disease and/or other forms of dementia relatively early in life, usually by age 55. That is because Down syndrome and Alzheimer's disease are tied to the same gene.
Everyone who has Down syndrome has a three copies instead of the normal two copies of the twenty-first chromosome. This chromosome contains the genetic code for making proteins in the brain. Instead of just one or two copies a gene for making a destructive protein called beta-amyloid, people who have Down syndrome may have up to three. The destructive proteins that seem to cause Alzheimer's disease can start accumulating in the brain by the age of eight, and the destructive process that leads to Alzheimer's is active when most people who have Down syndrome are teenagers.
It's only been in the last 30 to 40 years that most children born with Down syndrome lived to adulthood. Only in the twenty-first century has the life expectancy increased to the point that they would show the symptoms of Alzheimer's. Debility and death naturally follow, but a few people who have the combination of problems seem to escape symptoms much longer than others, sometimes to the age of 70. What may be helpful?
- High cholesterol levels are associated with earlier onset of Alzheimer's in people who have Down syndrome. There is no proof that lowering cholesterol with statins will stop dementia in Down syndrome, but there are indications of benefit in other groups, so statins may be worth trying. The level at which cholesterol makes a difference is 200 mg/dl (about 5.2 mmol/L).
- Iron overload is also associated with earlier onset of dementia in people who have Down syndrome. It is critical not to give iron supplements unless there has been a blood test that confirms iron deficiency.
- Vitamin supplements, unfortunately don't make a difference in slowing down the arrival of Alzheimer's disease. Supplemental vitamin E is actually associated with more complications, not fewer.