Muscular Dystrophy-Dystroglycanopathy (Congenital Without Mental Retardation), Type B, 4

A number sign (#) is used with this entry because this form of congenital muscular dystrophy-dystroglycanopathy without mental retardation (type B4; MDDGB4) is caused by compound heterozygous mutation in the gene encoding fukutin (FKTN; 607440) on chromosome 9q31.

Mutation in the FKTN gene can also cause a more severe congenital muscular dystrophy-dystroglycanopathy with brain and eye anomalies (type A4; MDDGA4; 253800) and a less severe limb-girdle muscular dystrophy-dystroglycanopathy (type C4; MGDGC4; 611588).

Description

MDDGB4 is a rare autosomal recessive congenital muscular dystrophy that is part of a group of similar disorders resulting from defective glycosylation of alpha-dystroglycan (DAG1; 128239), collectively known as 'dystroglycanopathies.' In contrast to most dystroglycanopathies, mental retardation is not a feature of MDDGB4 (Godfrey et al., 2007).

For a discussion of genetic heterogeneity of congenital muscular dystrophy-dystroglycanopathy type B, see MDDGB1 (613155).

Clinical Features

Godfrey et al. (2007) identified 1 patient with FKTN-related congenital muscular dystrophy among 92 probands with muscular dystrophy and evidence of a dystroglycanopathy. Although clinical details were limited, the age at onset was noted as 3 years, and the patient only achieved sitting. Other features included increased serum creatine kinase, generalized weakness, and mild white matter changes on brain MRI. The patient did not have mental retardation.

Molecular Genetics

Mercuri et al. (2009) identified compound heterozygosity for 2 mutations in the FKTN gene (R307Q; 607440.0009 and 42delG; 607440.0019) in 1 of 81 Italian patients with congenital muscular dystrophy associated with defective glycosylation of alpha-dystroglycan. The patient did not have mental retardation and had no structural brain abnormalities.