Prenatal diagnosis by amniocentesis and chorionic villus biopsy of mtDNA mutation 8993T > G.

The mtDNA mutation 8993T > G is associated with neurogenic muscle weakness, ataxia and retinitis pigmentosa (NARP) and Leigh syndrome. There are few reported cases of prenatal testing for mtDNA disorders. Specifically for 8993T > G, there are six cases in which prenatal diagnosis has been reported. We describe prenatal diagnosis in a 36-year-old G3P1 woman with 33% heteroplasmy in white blood cells. She had a previous child who died from Leigh disease (92% heteroplasmy). She underwent prenatal testing by both CVS and amniocentesis of the 8993T > G heteroplasmy levels. This is the first reported case in which both procedures were used. Heteroplasmy was similar in both tissues (58.6% CVS and 55% amniocentesis), in support of the theory that this testing is reliable and may be considered in prenatal cases where this mutation is known in the mother. To date, her child is 20 months old and developing normally. Heteroplasmy determination in the child was refused. Although the infant is developmentally normal, consistent with the observation that levels of heteroplasmy below 60% are compatible with a mild phenotype, this conclusion must be tempered by the limited period of observation and the fact that patients with the NARP phenotype often present later than 20 months of age.

Genomic sequencing of the bovine T cell receptor beta locus.

The T cell, which plays an integral role in the coordination of the immune system, has a heterodimer receptor (TCR) that can exist in one of the two forms: alpha/beta or gamma/delta. Cells displaying the gamma/delta TCR comprise less than 5% of T cell populations in humans and mice. In the bovine system, however, gamma/delta populations can reach as high as 60%. Differences in T cell populations make the bovine system an excellent candidate for genomic TCR sequencing and multi-species comparisons. In an effort to characterize the bovine TCR loci, a genomic library was screened for the beta TCR gene. A shotgun sequencing library was constructed and preliminary analysis demonstrates that the organization of the bovine TCR beta constant regions is different from both humans and mice. The bovine beta locus appears to have a third constant region. Overall, the genomic characterization of the bovine TCR genes will provide insight into the evolution of T cell receptor.