Shapiro and Yen (1987) responded to the suggestion that the condition in these patients may represent a microcytogenetic disorder ( Schmickel, 1986 ). They stated that homologous but nonfunctional sequences of STS were found on the long arm of the Y chromosome in the patients of Sunohara et al. (1986) . Indeed, they found a complete deletion of the STS gene with continued presence of MIC2 ( 313470 ) sequences, which are located more distally on the X chromosome, in both the X and Y chromosomes. In studies of 9 unrelated patients with simple X-linked ichthyosis, they found 7 with complete deletion of the STS gene and 1 with a partial 5-prime deletion. Only 1 subject had an intact STS gene.

Hardelin et al. (1993) reported results of a mutation search of the KAL1 gene in 21 unrelated males with familial Kallmann syndrome. In 2 families, large deletions that included the entire KAL gene were detected by Southern blot analysis. By sequencing each of the 14 coding exons and splice site junctions in the other 19 patients, they found 9 point mutations at separate locations in 4 exons and 1 splice site. They emphasized the high frequency of unilateral renal aplasia in X-linked Kallmann syndrome patients; 6 of 11 males with identified alterations of the KAL gene showed this feature.

Multiplex-PCR consists of multiple primer sets within a single PCR mixture to produce amplicons of varying sizes that are specific to different DNA sequences. By targeting multiple sequences at once, additional information may be gained from a single test run that otherwise would require several times the reagents and more time to perform. Annealing temperatures for each of the primer sets must be optimized to work correctly within a single reaction, and amplicon sizes, ., their base pair length, should be different enough to form distinct bands when visualized by gel electrophoresis . Alternatively, if amplicon sizes overlap, the different amplicons may be differentiated and visualised using primers that have been dyed with different colour fluorescent dyes. Commercial multiplexing kits for PCR are available and used by many forensic laboratories to amplify degraded DNA samples.