Multiple endocrine neoplasia type 2A (MEN 2A) is a dominantly inherited cancer syndrome that affects tissues derived from neural ectoderm. It is characterized by medullary thyroid carcinoma (MTC) and phaeochromocytoma. The MEN2A gene has recently been localized by a combination of genetic and physical mapping techniques to a 480-kilobase region in chromosome 10q11.2 (refs 2,3). The DNA segment encompasses the RET proto-oncogene, a receptor tyrosine kinase gene expressed in MTC and phaeochromocytoma and at lower levels in normal human thyroid. This suggested RET as a candidate for the MEN2A gene. We have identified missense mutations of the RET proto-oncogene in 20 of 23 apparently distinct MEN 2A families, but not in 23 normal controls. Further, 19 of these 20 mutations affect the same conserved cysteine residue at the boundary of the RET extracellular and transmembrane domains.

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD), a much milder form of the disease where the age of onset can sometimes be as late as the third or fourth decade of life, are caused by mutations in the same X-linked gene, a 14 kilobase (kb) transcript which is spread over more than 2 megabases of the human X chromosome. The corresponding protein, dystrophin, has a relative molecular mass of 400,000. Most mutations causing DMD and BMD are deletions and deletions associated with both phenotypes are observed throughout the gene sequence. This observation led to the suggestion that DMD patients possess deletions that disrupt the reading frame of the protein, whereas BMD patients have deletions that retain the translational reading frame and enable the muscle cells to produce altered dystrophin products. This theory is supported by immunoblotting studies, which show that DMD patients lack dystrophin in their muscle cells or that dystrophin is present at very low levels, whereas BMD patients produce a protein with reduced abundance or abnormal size. Here we describe a deletion of the dystrophin gene in a family segregating for very mild BMD, one member of which was still ambulant at age 61 years, which removes a central part of the dystrophin gene encompassing 5,106 base pairs of coding sequence, almost half the coding information. Immunological analysis of muscle from one of the patients demonstrates that this mutation results in the production of a truncated polypeptide localized correctly in the muscle cell. These results are particularly significant in the context of gene therapy which, if it is ever envisaged, would be facilitated by the replacement of the very large dystrophin gene with a more manipulatable mini-gene construct.

The Duchenne muscular dystrophy (DMD) gene has been localized to chromosome Xp21 and codes for a 14-kilobase (kb) transcript and a protein called dystrophin, of relative molecular mass 427,000. Dystrophin is associated with the cytoplasmic face of muscle fibre membranes and its C-terminal domain is thought to mediate membrane attachment. Although N-terminal and central domain structures share common features with other cytoskeletal components, no significant sequence similarity between the C-terminal region of dystrophin and other previously characterized proteins has been described. Here we report that fragments from the C-terminal domain of the DMD complementary DNA detect a closely related sequence which exhibits nucleic-acid and predicted amino-acid identities with dystrophin of approximately 65 and 80%, respectively. The dystrophin-related sequence identifies a 13-kb transcript in human fetal muscle and maps to chromosome 6. Thus, dystrophin may be a member of a family of functionally related large structural proteins in muscle.

BackgroundSudden arrhythmic death syndrome (SADS) describes a sudden death with negative autopsy and toxicological analysis. Cardiac genetic disease is a likely etiology.ObjectivesThis study investigated the clinical utility and combined yield of post-mortem genetic testing (molecular autopsy) in cases of SADS and comprehensive clinical evaluation of surviving relatives.MethodsWe evaluated 302 expertly validated SADS cases with suitable DNA (median age: 24 years; 65% males) who underwent next-generation sequencing using an extended panel of 77 primary electrical disorder and cardiomyopathy genes. Pathogenic and likely pathogenic variants were classified using American College of Medical Genetics (ACMG) consensus guidelines. The yield of combined molecular autopsy and clinical evaluation in 82 surviving families was evaluated. A gene-level rare variant association analysis was conducted in SADS cases versus controls.ResultsA clinically actionable pathogenic or likely pathogenic variant was identified in 40 of 302 cases (13%). The main etiologies established were catecholaminergic polymorphic ventricular tachycardia and long QT syndrome (17 [6%] and 11 [4%], respectively). Gene-based rare variants association analysis showed enrichment of rare predicted deleterious variants in RYR2 (p = 5 × 10-5). Combining molecular autopsy with clinical evaluation in surviving families increased diagnostic yield from 26% to 39%.ConclusionsMolecular autopsy for electrical disorder and cardiomyopathy genes, using ACMG guidelines for variant classification, identified a modest but realistic yield in SADS. Our data highlighted the predominant role of catecholaminergic polymorphic ventricular tachycardia and long QT syndrome, especially the RYR2 gene, as well as the minimal yield from other genes. Furthermore, we showed the enhanced utility of combined clinical and genetic evaluation.