HMM: Form of B12 deficiency in cerebral spinal fluid found to negatively affect the central nervous system. “In 2014, a team of doctors found themselves having difficulty diagnosing a 67-year-old female patient with symptoms typically associated with B12 deficiency—she had difficulty speaking, tremors and ataxia. Blood tests showed no B12 deficiency. . . . The team conducted a spinal tap to analyze the patients’ cerebral spinal fluid. What came back was a surprise—the patient had almost no B12 in the fluid that bathes the brain and central nervous system, suggesting something was preventing it from crossing the blood brain barrier.”