The limb girdle muscular dystrophies: our ever-expanding knowledge

Inferring the effect of genomic variation in the new era of genomics

Accurate and detailed understanding of the effects of variants in the coding and noncoding regions of the genome is the next big challenge in the new genomic era of personalized medicine, especially to tackle newer findings of genetic and phenotypic heterogeneity of diseases. This is necessary to resolve the gene-variant-disease relationship, the pathogenic variant spectrum of genes, pathogenic variants with variable clinical consequences, and multiloci diseases. In turn, this will facilitate patient recruitment for relevant clinical trials. In this review, we describe the trends in research at the intersection of basic and clinical genomics aiming to (a) overcome molecular diagnostic challenges and increase the clinical utility of next-generation sequencing (NGS) platforms, (b) elucidate variants associated with disease, (c) determine overall genomic complexity including epistasis, complex inheritance patterns such as "synergistic heterozygosity," digenic/multigenic inheritance, modifier effect, and rare variant load. We describe the newly emerging field of integrated functional genomics, in vivo or in vitro large-scale functional approaches, statistical bioinformatics algorithms that support NGS genomics data to interpret variants for timely clinical diagnostics and disease management. Thus, facilitating the discovery of new therapeutic or biomarker options, and their roles in the future of personalized medicine.

The Case for Laboratory Developed Procedures: Quality and Positive Impact on Patient Care

An explosion of knowledge and technology is revolutionizing medicine and patient care. Novel testing must be brought to the clinic with safety and accuracy, but also in a timely and cost-effective manner, so that patients can benefit and laboratories can offer testing consistent with current guidelines. Under the oversight provided by the Clinical Laboratory Improvement Amendments, laboratories have been able to develop and optimize laboratory procedures for use in-house. Quality improvement programs, interlaboratory comparisons, and the ability of laboratories to adjust assays as needed to improve results, utilize new sample types, or incorporate new mutations, information, or technologies are positive aspects of Clinical Laboratory Improvement Amendments oversight of laboratory-developed procedures. Laboratories have a long history of successful service to patients operating under Clinical Laboratory Improvement Amendments. A series of detailed clinical examples illustrating the quality and positive impact of laboratory-developed procedures on patient care is provided. These examples also demonstrate how Clinical Laboratory Improvement Amendments oversight ensures accurate, reliable, and reproducible testing in clinical laboratories.

Founder mutation for α-sarcoglycan-LGMD2D in a Magdalen Islands Acadian cluster

BACKGROUND

We have recruited a group of four living and reviewed the records of six deceased distantly related French-Canadians of Acadian descent affected by a childhood-onset form of recessive limb-girdle muscular dystrophy (LGMD). All cases originate from the small archipelago of the Magdalen Islands (population: 13,000) isolated in the Gulf of St-Lawrence.

METHODS

Based on the likely sharing of the same founder mutation we completed a 319K SNPs genome-wide scan to identify the disease locus and then screen candidate genes in this region.

RESULTS

All patients had normal initial motor milestones. They presented with limb girdle weakness at the average age of seven years (5-11). Progressive weakness led to loss of ambulation at a wide range of ages (10-39). Patients also developed macroglossia, large calves and mild to moderate contractures, hyperlordosis and decreased pulmonary function. Creatine kinase levels were elevated (1,800-10,000 U/L) in the first decades, but decreased with progression of disease. Homozygosity mapping uncovered a shared chromosomal region of 6.33Mb. The alpha sarcoglycan (SGCA) gene, mutated in LGMD2D, lay in this candidate interval. Sequencing of all SGCA exons uncovered a shared homozygous missense mutation (c. 229C>T, p.R77C), the most common SGCA mutation internationally reported. Using demographic data, we estimated a high carrier rate of 1/22.

CONCLUSION

The p.R77C mutation has also been observed in many populations, including in France and Spain (Basques). This corresponds to the first reported recessive founder disease for the Magdalen Islands, an archipelago settled in the XIXth century, largely by Acadian immigrants.

Normal vaginal delivery in a patient with autosomal recessive limb-girdle muscular dystrophy

The limb-girdle muscular dystrophies (LGMDs) are a group of genetically determined disorders of skeletal muscle, predominantly affecting the pelvic and shoulder-girdle musculature. The clinical course is variable but steadily progressive. Type 2A LGMD is the most frequent form, accounting for approximately 30% of identified cases. There are few reports of patients with Type 2A LGMD undergoing pregnancy and delivery. This case outlines a successful vaginal delivery in a woman with this condition.

Proximal muscle weakness in a 15-year-old boy

Proximal muscle weakness, often indicative of a myopathy, has a broad differential diagnosis in children. We present a case of an adolescent boy with proximal weakness and a mildly elevated creatine kinase. He was found to have spinal muscular atrophy type III rather than a myopathy.