Genetic neuromuscular disorders have a range of inheritance patterns, some of which allow transmission of a gene mutation through unaffected carriers and may result in an affected child with no previous family history. In addition, gene mutations that cause neuromuscular disorders may happen for the first time (de novo) in an affected child.
A complete family history should include information about at least 3 generations, a question about consanguinity in the parents, and a summary question about whether anyone else in the family had muscle concerns or weakness.
A three-generation family history in the pediatric context includes information on the child’s generation (i.e., siblings and cousins), the parents’ generation (i.e., the parents and their siblings and cousins), and the grandparents’ generation (i.e., the grandparents and their siblings). Asking about consanguinity (whether the parents are related) is important because consanguinity increases suspicion of an autosomal recessive disorder.
Neuromuscular diseases have different inheritance patterns.
Neuromuscular disorders may be autosomal dominant (passing from affected parent to child 50% of the time), autosomal recessive (passing from two unaffected, carrier parents to child 25% of the time), or X-linked (passing from an unaffected carrier mother to a child (almost always a son) 50% of the time).
For those diseases that are X-linked (such as Duchenne and Emery Dreifuss muscular dystrophies and some of the Charcot Marie Tooth disorders), pay particular attention to the extended maternal family (i.e., ask if the mother and maternal grandmother have brothers, and are there any concerns?).
Signs of proximal muscle weakness include: abdominal breathing or accessory muscle use; a feeling of "slipping through hands" when held suspended by examiner under armpits; inability to voluntarily flex neck when supine or head lag when pulled to sit; difficulty rising from floor (including Gowers maneuver, full or modified) MORE CLINICAL PEARLS
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