New diagnostic method for Pallister‐Killian syndrome: Detection of i(12p) in interphase nuclei of buccal mucosa by fluorscence in situ hybridization

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Abstract
Detection of the supernumerary isochromosome 12p [i(12p)] was performed on buccal smear preparations from 2 patients with Pallister‐Killian syndrome, 21 (patient 1) and 15 months (patient 2) old, by interphase fluorescence in situ hybridization (FISH) using a chromosome 12‐specific alpha satellite probe. Isochromosome 12p‐positive cells were identified by observing 3 signals over the nucleus, while diploid cells had 2 signals. The proportion of i(12p)‐positive cells thus identified was high in the epithlial cells of buccal mucosa at 68 and 53% from patients 1 and 2, respectively. Further, the frequencies of i(12p)‐positive cells were also studied in PHA‐stimulated peripheral lymphocytes, cultured skin fibroblasts (both patients), and directly harvested T and B‐cells (patient 1). Of these tissues, buccal mucosa showed the highest proportion of i(12p)‐positive cells. These findings indicate that epithelial cells of buccal mucosa are likely to retain i(12p)‐positive cells. Detection of i(12p) using direct buccal smear preparations by interphase FISH is a rapid, effective and non‐invasive method for confirming the diagnosis of the Pallister‐Killian syndrome.