OBJECTIVE This is an up-to-date analysis of congenital muscular dystrophies (CMD), especially merosin-deficient-CMD, we also present our center expertise. METHODS CMD are skeletal muscle degenerative hereditary diseases caused by abnormal synthesis of structural or functional muscle proteins. Severe hypotonia, joint deformities and muscle weakness at birth are the main features of CMD. A especial type of CMD caused by absence of alpha 2 chain (or merosin) of laminin 2, a tissue specific protein from muscle basement membrane which anchors extracellular matrix to dystrophin, is the paradigm of a muscular dystrophy produced by extracellular abnormalities. CMD merosin-negative locus was assigned to chromosome 6q2, where is localized the laminin alpha 2 chain gene (LAMA2). Recently, LAMA2 gene mutations producing the disease have been described. Floppy infant syndrome is its earliest symptom and CMD merosin-negative represents the most frequent cause of muscular origin. 40% of our CMD patients are completely merorin-deficient. They had marked delayed motor milestones and never became ambulant but their intelligence remainded normal. Nowadays we can perform a prenatal diagnosis by immunohistochemical analysis in trophoblast. CONCLUSIONS CMD merosin-deficient represents a subset of patients with a potentially poor prognosis, thus an early diagnosis is highly convenient in order to establish a correct follow-up [REV NEUROL 1999; 28: 141-9].