Laboratory Issues

If the etiology of developmental delay or MR in a patient is unknown, DNA analysis should be performed as part of a comprehensive genetic evaluation that includes routine cytogenetic analysis (karyotyping). Cytogenetic abnormalities, including unbalanced translocations and deletions, have been identified in individuals referred for testing for PWS or AS. Although it is not necessary for every lab oratory to provide all testing methodologies, a smooth progression through the various testing types may be necessary to determine the genetic mechanism causing PWS or AS, and is facilitated if the laboratory is able to perform at least DNA methylation, UPD, and FISH analyses. If sequencing of the UBE3A gene is necessary, testing may be referred to a clinical laboratory offering this test. Mutation analysis of the IC is available only on a research basis.

The SNRPN probe for Southern blot analysis is available from American Type Culture Collection (http://www.atcc.

org). Many laboratories use laboratory-developed testing methods for methylation-sensitive PCR or RT-PCR analysis. Oligonucleotide primers for amplification of marker loci for UPD analysis can be synthesized or obtained commercially. FISH probes are available from two commercial sources (Cytocell, Inc, and Vysis, Inc). Patient control cell lines may be purchased from the Coriell Cell Repositories (http://coriell.umdnj.edu/). The proficiency tests for molecular genetics provided by the CAP include specimens for PWS and AS testing.

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