Narrowing the Duane syndrome critical region at chromosome 8q13 down to 40 kb

Duane syndrome (MIM 126800) is an autosomal dominant disorder characterised by primary strabismus and other ocular anomalies, associated with variable deficiency of binocular sight. We have recently identified a < 3 cM smallest region of deletion overlap (SRO) by comparing interstitial deletions at band 8q13 in two patients (one described by Vincent et al, 1994, and the other by Calabrese et al, 1998). Here we report on another patient with Duane syndrome carrying a reciprocal translation t(6;8)(q26;q13). FISH and PCR analyses using a YAC contig spanning the SRO narrowed the Duane region to a < 1 cM interval between markers SHGC37325 and W14901. In addition, the identification and mapping of two PAC clones flanking the translocation breakpoint, allowed us to further narrow the critical region to about 40 kb. As part of these mapping studies, we have also refined the map position of AMYB, a putative candidate gene, to 8q13, centromeric to Duane locus. AMYB is expressed in brain cortex and genital crests and has been previously mapped to 8q22.