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SlR-kuCOCyte cultures for chromosome analysis generally rely on the glycoprotein phytohaemagglutinin to stimulate T-cells into a transient blastic transformation so that metaphase chromosomes can be obtained after 3 days in cu1ture.l Success rates are greater than 98% (UK NEQAS data) and a single repeat sample is usually sufficient to produce a result whenever an initial culture fails. Over the past 5 years, however, we have encountered three patients in whom cultures failed on more than two occasions and in each case a diagnosis associated with immunodeficiency was reached. Patient 1 was referred at 13 months of age for global developmental delay, gross motor delay, and macrocephaly. A few poor-quality metaphases with apparently normal chromosomes were obtained and two further samples at 19 and 2 1 months yielded no metaphases. Subsequently, however, biochemical analysis’ revealed purine nucleotide phosphorylase (PNP) deficiency which is an established cause of severe T-cell dysfunction. PNP is an autosomal recessive condition in which mutations of the PNP gene |
