Congenital myotonic dystrophy: case report

Abstract

Myotonic dystrophy or Steinert’s disease has the second highest incidence in childhood, immediately after progressive musculardystrophies (Duchenne and Becker). The incidence in general population is 1:8000 in Europe and 1:30000 in Croatia. This disease isinherited in an autosomal dominant manner. The gene is located on the long arm of chromosome 19 (19q13), gene product is myotoninprotein kinase. The disease develops due to pathologic multiplication of the identical CTG trinucleotide repeat inside the noncodingregion of the myotonin protein kinase gene (DMPK). The number of repeating CTG triplets ranges from 5 to 34 and it remainsstable in healthy persons through generations. Diseased people have the extended sequence that consists of 50 to several thousandCTG trinucleotides, and the severity of the clinical picture and the disease occurrence correlate with the size of the expansion. Peoplewith 35-49 triplets are healthy disease carriers. Mutation is more often transmitted by the mother and every next generation carriesmolecular and clinically more severe mutation. Myotonic dystrophy manifests with symptoms in several organic systems: skeletalstriated muscles and smooth intestinal muscles are aff ected, as well as cardiac muscle and its conductive system, endocrine andimmune system, with development of cataract, intellectual disability and neurologic defi cits. This study presents a male infant withgeneralized hypotonia, facial dysmorphism, feeble mime, feeding diffi culties and feet deformities. Family history revealed his 7-yearoldbrother to be clinically suspected of facioscapulohumeral muscular dystrophy. Targeted neurological examination of the mothershowed weakness of facial muscles, inability to fully close her eyes, action myotonia of the hands and percussion myotonia of thetongue, all of these pointing to molecular genetic analysis which determined full mutation allele and the need of genetic examinationof the whole family.