Purpose:To study brain MRI findings in patients with 18qϪ syndrome and to correlate these findings with the results of the molecular breakpoint analysis. Materials and Methods:Brain MR images of 17 patients with 18qϪ syndrome were evaluated. Segregation analysis was performed with 15 microsatellite markers to determine the deletion breakpoints and whether the deletion included the myelin basic protein (MBP) gene. Results:One patient had an interstitial deletion of 18q which spared the MBP gene. He was the only one with normal brain MRI. All 16 patients with deletions including the MBP gene had abnormal white matter in MRI. The main finding was poor differentiation of gray and white matter on T2-weighted images due to increased white matter signal intensity. In addition, measured signal intensity of the white matter was significantly increased in patients compared with controls. Conclusions:Poor differentiation of gray and white matter on T2-weighted images is the most typical MRI finding of the 18qϪ syndrome. These results support the postulation that abnormal myelination in 18qϪ syndrome is due to haploinsufficiency at or near the MBP locus.

Three DNA probes (APOC2, PSC11, and LDR152) detecting RFLP polymorphisms were used to test the usefulness of the RFLP approach in myotonic dystrophy (MD) families from the isolated Finnish population. The informativeness of these polymorphisms did not differ from that reported in more mixed populations: in the 13 families of the study most of the 79 meiotic events studied were informative. One known recombinant is included in the study. The highest lod score obtained in the multilocus linkage analysis was z = 5.941 at recombination fraction theta = 0.02. The RFLP results significantly facilitated genetic counseling in problematic cases among the families studied. Although evidence could be found for linkage disequilibrium of the RFLP haplotypes formed in Finnish MD patients, our results do not exclude the possible existence of more than one ancient MD mutation in this population.