Mapping of two new markers within the smallest interval harboring the spinal muscular atrophy locus by family and radiation hybrid analysis.

The locus responsible for the childhood-onset proximal spinal muscular atrophies (SMA) has recently been mapped to an area of 2-3 Mb in the region q12-q13.3 of chromosome 5. We have used a series of radiation hybrids (RHs) containing distinct parts of the SMA region as defined by reference markers. A cosmid library was constructed from one RH. Thirteen clones were isolated and five of these were mapped within the SMA region. Both RH mapping and fluorescence in situ hybridization analysis showed that two clones map in the region between loci D5S125 and D5S351. One of the cosmids contains expressed sequences. Polymorphic dinucleotide repeats were identified in both clones and used for segregation analysis of key recombinant SMA families. One recombination between the SMA locus and the new marker 9Ic (D5S685) indicates that 9Ic is probably the closest distal marker. The absence of recombination between the SMA locus and marker Fc (D5S684) suggests that Fc is located close to the disease gene. These new loci should refine linkage analysis in SMA family studies and may facilitate the isolation of the disease gene.

Demonstration of the genuine iso-12p character of the standard marker chromosome of testicular germ cell tumors and identification of further chromosome 12 aberrations by competitive in situ hybridization.

The recently developed competitive in situ hybridization (CISH) strategy was applied to the analysis of chromosome 12 aberrations in testicular germ cell tumors (TGCTs). DNAs from two rodent-human somatic cell hybrids, containing either a normal chromosome 12 or the p arm of chromosome 12 as their unique human material, were used as probes. Our results demonstrate a genuine iso-12p character of the standard marker chromosome in TGCTs. Moreover, variant markers were identified representing translocation products that also involve chromosome 12.