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MCD1A represents 30-40% of congenital muscular dystrophies, with some regional variation. Prevalence is estimated at 1/30,000.

The disease presents at birth or in the first few months of life with hypotonia and muscle weakness in the limbs and trunk. Respiratory and feeding disorders can also occur. Motor development is delayed and limited (sitting or standing is only possible with help). Infants present with early rigidity of the vertebral column, scoliosis, and respiratory insufficiency. There is facial involvement with a typical elongated myopathic face and ocular ophthalmoplegia disorders can appear later. Epileptic attacks are possible, although they occur in less than a third of patients. Intellectual development is normal.

MCD1A is caused by mutations in the LAMA2 gene coding for the alpha-2 laminin chain.

Diagnosis is based on muscular biopsy, as merosin deficiency can be detected in the muscle and skin. MRI reveals diffuse abnormalities in brain white matter, typically sparing the corpus callosum, capsula interna and cerebellum. In the initial phase of the disease there is a four-fold increase in levels of serous creatine kinase.

Differential diagnoses include other forms of congenital muscular dystrophy, linked particularly with glycosylation and alpha-dystroglycan anomalies, as well as congenital structural myopathies (central core disease, multi-minicore myopathy, centronuclear myopathy), of which the causative genes have been identified in the majority of cases (see these terms).

Prenatal diagnosis is possible in the ninth week by chorionic villus sampling for evidence of merosin deficiency, and by evidence of mutation in the LAMA2 gene.

Transmission is autosomal recessive. Genetic counseling should be offered to families.

Treatment is symptomatic. It consists of a multidisciplinary approach, including physiotherapists, occupational therapists and speech-language therapists, with the objective of optimizing each patient's abilities. Seizures or other neurological complications require specific treatment.

The prognosis of these muscular dystrophies is very severe as a large proportion of affected children do not reach adolescence. Currently, the prognosis can only be improved by attentive multidisciplinary (particularly orthopedic and respiratory) management.