Unusual clinical features in infantile Spinal Muscular Atrophies

Spinal Muscular Atrophies (SMA) are a group of degenerative diseases primarily affecting the anterior horn cells of the spinal cord and resulting in muscle weakness and atrophy. Diagnostic criteria were proposed by the International SMA Consortium (ISMAC) to differentiate"classical" proximal SMA caused by homozygous deletion or conversion of the SMN1 gene (5q13) from atypical SMA unlinked to chromosome 5q (non-5q-SMA entities). The aim of our study was to emphasize the unusual clinical features encountered in infantile SMA.

We retrospectively analyzed 63 children with SMA hospitalized between 1985 and 2006.

Forty-eight children suffered from classical SMA and 15 from atypical SMA, including 4 distal SMA, 2 scapuloperoneal SMA, one pontocerebellar hypoplasia type I, 7 neurogenic arthrogryposis multiplex congenita (2 of them associated with a central nervous system (CNS) involvement) and one undetermined case.

This study confirmed the clinical variety of proximal SMA and put in perspective some exclusion criteria (CNS involvement, phrenic or facial palsy). Some symptoms allowed us to anticipate the normality of the SMN1 gene: improvement of motor condition, distal predominance and, more relatively, assymetry of motor weakness. Diagnosis difficulties were especially encountered in case of predominant distal deficit, arthrogryposis multiplex congenita and associated clinical abnormalities. Detailed phenotypical description and syndromic regrouping of cases of atypical SMA lead to a better understanding of underlying physiopathological processes and to the identification of other genes involved in infantile SMA.