Cerebral blood flow and perfusion measured by SPECT (Xenon and Tc-HMPAO), MRI findings, and neuropsychological function in 22 patients with myotonic dydtrophy (MD) were studied at the Departments of Neurology, Radiology, Psychiatry, and Pediatrics, Harbor-UCLA Medical Center, Torrance, CA. Results in 8 patients with maternal (mMD) inheritance were compared with those in 11 with paternal (pMD) inheritance, and in 10 normal controls. Patients with mMD had significantly lower scores on IQ tests and more extensive cerebral hypoperfusion when compared to those with pMD. Decreases in cerebral blood flow, most severe in frontal and temporoparietal association cortex, correlated strongly with lower scores on IQ tests. Patients with mMD had earlier onset of illness than the pMD group (means, 6.3 vs 32 yrs). Cerebral hypoperfusion patterns in the mMD patients were consistent with diffuse brain injury, whereas pMD patients showed only minor changes. 
COMMENT. Mothers with myotonic dystrophy should be warned that their children would have a high probability of mental retardation. Hypoxic injury in utero is suggested as the likely explanation for the brain injury. Milder abnormalities in cerebral blood flow seen in the pMD group were attributed to possible sleep apnea, since many had hypersomnolence.