ATLANTA , Georgia ( CNN ) -- Four prominent neurologists say they can not see how Sen. Pete Domenici can continue his work as a U.S. senator given his diagnosis with frontotemporal lobar degeneration , a type of dementia . September tests showed Sen. Pete Domenici 's brain disorder had progressed since an April checkup . The disease attacks the frontal and temporal lobes of the brain , which control judgment , complex decision-making , communication , mood and behavior . None of the four doctors is treating Domenici , nor is any familiar with his case , but all have treated patients with frontotemporal lobar degeneration , or FTLD . Dr. David Knopman , a neurologist at the Mayo Clinic , says when his patients learn they have FTLD , he tells them it 's best to stop working . `` They would be prone to have poor judgment and make mistakes , '' Knopman said . `` I would encourage them to leave their employment . '' Domenici , a six-term New Mexico Republican , announced Thursday that he will not seek re-election after his current term expires in January 2009 . It 's not clear how long the senator has known of his condition . `` For at least two years , I have felt very little impact from this disease , '' he said in announcing his decision . But September tests showed the condition had progressed since a checkup in April , he said . `` While the progression was slight , I had to consider whether I could in good conscience run for re-election and serve you as well as you deserve for another six-year term , '' Domenici told an audience in Albuquerque , New Mexico . A source close to Domenici , 75 , says his physician at Johns Hopkins University Hospital `` has a comfort level with his ability to finish out the term . '' The source added , `` Those of us who work with him have not seen much deterioration . '' Dr. Bruce Miller , a neurologist at the University of California-San Francisco , says that of the 500 patients he 's treated for FTLD , very few have been able to keep working . `` At times they can shift to a different style of work that does n't require making big judgments , like being a paper boy , '' he said . Dr. Murray Grossman , a neurologist at the University of Pennsylvania , noted the difficulties the disease presents for people who make decisions on others ' behalf . `` A lawyer would n't be able to best defend their clients . A stockbroker would n't be able to make the best investments for their clients , '' he said . Another neurologist , Dr. Daniel Brauner , said if an FTLD patient is making `` world-shaking decisions they should probably stop working . '' He added some of his patients in less stressful jobs have been able to keep working but have had to scale back , leaving behind tasks that are too complex . In addition to problems with judgment , FTLD patients have behavior and language issues , because of the areas of the brain that are affected . `` They can be inappropriate with money . They believe every ad they see in the paper and buy everything , '' he said . The doctors said first signs of the disease are often very unusual behavior or a change in personality . An affectionate grandfather , for example , might push away a grandchild looking for a hug . Someone who 's always been very polite might become very rude . `` Someone who 's usually very adept and in touch with people might suddenly make inappropriate or caustic comments , like they might refer to someone who 's overweight as 'fatty , ' '' Knopman says . He added patients often do n't want to leave work . `` One of the problems with this disorder is they often lack insight so they themselves do n't perceive the problems , '' Knopman said . There 's no cure for FTLD . Treatment consists of managing symptoms with medication and in some cases , speech therapy . E-mail to a friend . Elizabeth Cohen is a correspondent with CNN Medical News . Senior producer Jennifer Pifer contributed to this report .
Experts : Most patients with frontotemporal lobar degeneration must stop working . FTLD affects parts of brain that govern judgment , complex decision-making . Senator 's doctor said to be comfortable with decision to finish term .