Prenatal diagnosis in merosin-deficient congenital muscular dystrophy

Prenatal Diagnosis of Merosin-Deficient Muscular Dystrophy

GOAL

We evaluated the potential for prenatal diagnosis of merosin-negative muscular dystrophies by immunohistochemistry.

MATERIALS AND METHODS

This is a retrospective study of 12 pregnancies with merosin-negative muscular dystrophy in a prior child. Chorionic villus sampling (CVS) was performed between 11th to 13th gestational weeks. Merosin immunohistochemical studies were performed on trophoblastic cells.

RESULTS

Two of 12 were "merosin-negative," both were from the same family. Fetal ultrasonographies were evaluated as normal in these pregnancies. Eight of the 10 merosin-positive cases delivered healthy babies. Two were lost to follow-up.

CONCLUSION

Prenatal diagnosis of merosin-negative muscular dystrophies can be accomplished by immunohistochemical analysis.

From proteins to genes: immunoanalysis in the diagnosis of muscular dystrophies

Muscular dystrophies are a large heterogeneous group of inherited diseases that cause progressive muscle weakness and permanent muscle damage. Very few muscular dystrophies show sufficient specific clinical features to allow a definite diagnosis. Because of the currently limited capacity to screen for numerous genes simultaneously, muscle biopsy is a time and cost-effective test for many of these disorders. Protein analysis interpreted in correlation with the clinical phenotype is a useful way of directing genetic testing in many types of muscular dystrophies. Immunohistochemistry and western blot are complementary techniques used to gather quantitative and qualitative information on the expression of proteins involved in this group of diseases. Immunoanalysis has a major diagnostic application mostly in recessive conditions where the absence of labelling for a particular protein is likely to indicate a defect in that gene. However, abnormalities in protein expression can vary from absence to very subtle reduction. It is good practice to test muscle biopsies with antibodies for several proteins simultaneously and to interpret the results in context. Indeed, there is a degree of direct or functional association between many of these proteins that is reflected by the presence of specific secondary abnormalities that are of value, especially when the diagnosis is not straightforward.

Congenital muscular dystrophies: new aspects of an expanding group of disorders

The congenital muscular dystrophies comprise a genetically and clinically heterogeneous group of disorders characterized by early onset of progressive muscle weakness and often involvement of other organ systems such as the brain and eyes. During the last decade, significant progress has been made to further characterize various forms of congenital muscular dystrophies based on their specific genetic and clinical appearance. This review represents an overview of the recent accomplishments as they relate to clinical, diagnostic, pathogenetic and therapeutic aspects of congenital muscular dystrophies.

Protein and DNA Analysis for the Prenatal Diagnosis of α2-Laminin–Deficient Congenital Muscular Dystrophy

Congenital muscular dystrophies (CMD) are characterized by neonatal hypotonia and/or artrogriposis associated with a dystrophic muscle biopsy. The CMD1A form is caused by a deficiency of the alpha2 chain of laminin 2 (LAMA2 gene at 6q2), a protein present in the basal lamina of muscle fibers, in Schwann cells, epidermis, and in fetal trophoblastic tissue. This allows its study for prenatal diagnosis in the chorionic villous (CV), which was performed in a family with one deceased affected CMD1A child. Immunohistochemical analysis of the CV using antibodies against the C- and N-terminal domains of the alpha2-laminin protein showed a normal positive labeling for both antibodies in the "at-risk" CV, which did not differ from the normal control CV. The integrity of the CV membrane was confirmed through the analysis with antibodies against alpha1, beta1, and gamma1 laminins. DNA study using markers flanking the 6q2 region showed that the affected patient and the "at-risk" fetus did not share the same haplotype. Therefore, the fetus was considered normal through both methodologies, which was confirmed after the birth of a clinically normal male baby. As the LAMA2 gene is very large and the spectrum of mutations causing disease is wide, the analysis of the protein in muscle biopsy has been largely used for the diagnosis. Besides, the possibility to detect it in the chorionic villous, mainly using positive markers, also offers a powerful tool for prenatal diagnosis.

Laminins and human disease

The laminin protein family has diverse tissue expression patterns and is involved in the pathology of a number of organs, including skin, muscle, and nerve. In the skin, laminins 5 and 6 contribute to dermal-epidermal cohesion, and mutations in the constituent chains result in the blistering phenotype observed in patients with junctional epidermolysis bullosa (JEB). Allelic heterogeneity is observed in patients with JEB: mutations that results in premature stop codons produce a more severe phenotype than do missense mutations. Gene therapy approaches are currently being studied in the treatment of this disease. A blistering phenotype is also observed in patients with acquired cicatricial pemphigoid (CP). Autoantibodies targeted against laminins 5 and 6 destabilize epithelial adhesion and are pathogenic. In muscle cells, laminin alpha 2 is a component of the bridge that links the actin cytoskeleton to the extracellular matrix. In patients with laminin alpha 2 mutations, the bridge is disrupted and mature muscle cells apoptose. Congenital muscular dystrophy (CMD) results. The role of laminin in diseases of the nervous system is less well defined, but the extracellular protein has been shown to serve an important role in peripheral nerve regeneration. The adhesive molecule influences neurite outgrowth, neural differentiation, and synapse formation. The broad spatial distribution of laminin gene products suggests that laminin may be involved in a number of diseases for which pathogenic mechanisms are still being unraveled.

Merosin-deficient congenital muscular dystrophy: neuropathology case reports

The aims of our study were: to present cases of congenital muscular dystrophy (CMD) with deficiency in merosin and the importance of immunohistochemistry in the diagnosis of merosin-deficient CMD. In four years (1997-2000), we found three patients with merosin-deficient CMD, one of them having an unusual clinical and pathological manifestation of the disease. Muscle biopsies of gastrocnemius or quadriceps muscles were investigated. In addition with the conventional HE staining, indirect immunohistochemistry for merosin, dystrophin, utrophin and for the proteins of the dystrophin associated complex (alpha-, beta-, gamma- sarcoglycans; beta-dystroglycan) was performed on cryosections. The findings suggest that there is no correlation between the clinical and histological picture of the disease and the expression of merosin in skeletal muscles. The degree of muscle involvment (assessed by histology) is parallel with the clinical neuromotor deficiency, but not with expression of merosin, which can be absent even in mild cases. The clinical investigations as well as current morphological techniques, only together with immunohistochemistry can differentiate between merosin - deficient CMD and other muscular dystrophy forms.

Pyogenic arthritis, pyoderma gangrenosum, and acne syndrome maps to chromosome 15q

Pyoderma gangrenosum, cystic acne, and aseptic arthritis are clinically distinct disorders within the broad class of inflammatory diseases. Although this triad of symptoms is rarely observed in a single patient, a three-generation kindred with autosomal-dominant transmission of these three disorders has been reported as "PAPA syndrome" (MIM 604416). We report mapping of a disease locus for familial pyoderma gangrenosum-acne-arthritis to the long arm of chromosome 15 (maximum two-point LOD score, 5.83; recombination fraction [straight theta] 0 at locus D15S206). Under the assumption of complete penetrance, haplotype analysis of recombination events defined a disease interval of 10 cM, between D15S1023 and D15S979. Successful identification of a single disease locus for this syndrome suggests that these clinically distinct disorders may share a genetic etiology. These data further indicate the role of genes outside the major histocompatibility locus in inflammatory disease.

Immunocytochemical analysis of human muscular dystrophy

Immunocytochemistry is an essential tool for the assessment of muscle biopsies from patients with muscular dystrophy, especially the recessive forms. Antibodies can detect primary defects when there is an alteration in expression, in particular in Xp21 muscular dystrophies, Emery-Dreifuss muscular dystrophy, the limb-girdle dystrophies caused by abnormal expression of the sarcoglycans, and in the form of congenital muscular dystrophy linked to the gene for laminin alpha2. Absence of a protein is easily observed and reduction in expression can be assessed provided adequate controls and baselines are established. Assessment of secondary defects can also be of diagnostic value; they widen the understanding of pathology changes, and are helping in the development of therapeutic strategies.

Laminin alpha2 deficient congenital muscular dystrophy: prenatal diagnosis

Laminin alpha2 chain-deficient congenital muscular dystrophy (CMD) is diagnosed by genetic analysis and by immunohistochemistry. Since laminin alpha2 chain is expressed in placental trophoblasts, the demonstration of its deficiency in chorionic villi is a useful aid to prenatal diagnosis. We present our experience with the use of the immunohistochemical method for prenatal diagnosis in four women, all of whom had at least one child with laminin alpha2 chain-deficient CMD. Immunohistochemistry provided a rapid procedure for prenatal diagnosis, and follow-up of these four cases confirmed its reliability.

Decade of the brain: neurological advances

In the last half century, neurological developments have been phenomenal and have escalated in this decade of the brain. Many infective disorders have been conquered, but AIDS has posed new challenges. Neuropharmacology has transformed the management of parkinsonism and epilepsy. New imaging techniques such as CT, NMR, PET and ultrasonic scanning have presented us with remarkable images of the nervous system in health and disease. Steroids control many autoimmune disorders; beta-interferon and other new drugs have begun to influence multiple sclerosis. Intensive care has saved many of those with head injury or acute neurological disorders, and we have greatly improved methods of rehabilitation. There are still many incurable neurological disorders but none are untreatable. Today's discovery in basic science brings tomorrow's improvement in patient care, as is clearly shown by molecular genetics. Some neurological and neuromuscular diseases in which the causal gene or genes have been located and characterised and in which the missing or abnormal gene product has been identified will be mentioned, as well as the prospects of carrier detection, antenatal diagnosis and gene therapy.