Advanced approach for comprehensive mtDNA genome testing in mitochondrial disease

Mitochondrial disease diagnosis requires interrogation of both nuclear and mitochondrial (mtDNA) genomes for single-nucleotide variants (SNVs) and copy number alterations, both in the proband and often maternal relatives, together with careful phenotype correlation. We developed a comprehensive mtDNA sequencing test ('MitoGenome') using long-range PCR (LR-PCR) to amplify the full length of the mtDNA genome followed by next generation sequencing (NGS) to accurately detect SNVs and large-scale mtDNA deletions (LSMD), combined with droplet digital PCR (ddPCR) for LSMD heteroplasmy quantification. Overall, MitoGenome tests were performed on 428 samples from 394 patients with suspected or confirmed mitochondrial disease. The positive yield was 11% (43/394), including 34 patients with pathogenic or likely pathogenic SNVs (the most common being m.3243A > G in 8/34 (24%) patients), 8 patients with single LSMD, and 3 patients with multiple LSMD exceeding 10% heteroplasmy levels. Two patients with both LSMD and pathogenic SNV were detected. Overall, this LR-PCR/NGS assay provides a highly accurate and comprehensive diagnostic method for simultaneous mtDNA SNV detection at heteroplasmy levels as low as 1% and LSMD detection at heteroplasmy levels below 10%. Inclusion of maternal samples for variant classification and ddPCR to quantify LSMD heteroplasmy levels further enables accurate pathogenicity assessment and clinical correlation interpretation of mtDNA genome sequence variants and copy number alterations.

The prenatal sonographic diagnosis of lethal multiple pterygium syndrome: a heritable cause of recurrent abortion

Presumably, a large number of recurrent abortions are caused by lethal recessive syndromes whose diagnosis depends either on a known family history or on the identification of characteristic fetal phenotypic features on pathologic examination. Because these conditions are rare, family histories are seldom helpful, and nondirected postmortem examinations on degenerating samples are seldom enlightening. Serial ultrasonography beginning early in pregnancy may provide important information in the evaluation of recurrent abortion caused by lethal recessive disorders. Reported is the accurate prenatal sonographic diagnosis of lethal multiple pterygium syndrome in a patient with a history of recurrent abortions. This syndrome is characterized by multiple limb contractures with pterygia, facial clefting, intracranial abnormalities, cystic hygroma, progressive fetal edema, and fetal death by midgestation. Inheritance may be X-linked recessive. Lethal multiple pterygium syndrome should be considered in patients with a history of recurrent midtrimester losses.