Congenital muscular dystrophy due to merosin deficiency is one of the most common congenital muscular dystrophies. It is characterized by a LAMA2 gene mutation and causes varied clinical symptoms depending on the type of presentation. In this case report, we identified the importance of the medical history and the autosomal recessive expression, which compromises the sequencing of the LAMA2 gene, with a mutation variant c. 1854_1861dup (p. Leu621Hisfs*7), in homozygosity not described so far. As well as the phenotypic characteristics of the evidenced mutation.A 13-year-old patient presented with a clinical history that began at 18 months of age. According to the mother, the patient had a delay in neurological development and could not walk since he was 7. In addition, contractures were observed in the lower extremity, elbows, and fingers of both hands. The patient also had scoliosis, bilateral hip dysplasia, and sleep apnea-hypopnea syndrome. However, cognitive function was unaffected. Extension studies revealed elevated creatine kinase levels, electromyography indicated muscle fiber involvement, and brain resonance imaging showed a hyperintense lesion at the periventricular level along with symmetrical supratentorial findings. Immunohistochemical studies of merosin showed incomplete reactivity and gene sequencing revealed evidence of a LAMA2 mutation: c. 1854_1861dup (p. Leu621Hisfs*7), in homozygosity.Congenital muscular dystrophy caused by merosin deficiency is characterized by the absence of laminin alpha-2. The clinical manifestation of this disease is a severe phenotype, mainly due to the early onset of the disease. In patients with mutations in the LAMA2 gene, the absence or partial reduction of laminin alpha-2 staining may allow some degree of ambulation, as it could indicate a partially functional protein. To complement clinical, immunohistochemical, and pathologic findings, ultrasound can be used as a potential tool for monitoring or assisting in the diagnosis of individuals with congenital muscular dystrophy. In this study, we performed sequencing of the LAMA2 gene, which revealed a homozygous c. 1854_1861dup (p. Leu621Hisfs*7) mutation. In addition, we describe the phenotypic features associated with this specific mutation.