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.

XLI can be suspected based on clinical findings, although symptoms can take varying amounts of time to become evident, from a few hours after birth, up to a year in milder cases. The diagnosis is usually made by a dermatologist , who also typically formulates the treatment plan (see below). STS enzyme deficiency is confirmed using a clinically available biochemical assay. Carrier detection can be performed in mothers of affected sons using this test (see Genetics, below). [10] Molecular testing for DNA deletions or mutations is also offered, and can be particularly useful in the evaluation of individuals with associated medical conditions (see below). Prenatal diagnosis is possible using either biochemical or molecular tests. However, the use of prenatal diagnosis for genetic conditions that are considered to be generally benign raises serious ethical considerations and requires detailed genetic counseling.

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.