Duchenne muscular dystrophy coexisting with Down syndrome or Turner syndrome: Two case reports

<h4>Background</h4>Dystrophinopathies are X-linked recessive neuromuscular disorders caused by pathogenic variants in the dystrophin gene (<i>DMD</i>). Down syndrome (DS) and Turner syndrome (TS) are well-characterized chromosomal conditions; however, their co-occurrence with monogenic disorders such as Duchenne muscular dystrophy (DMD) is rare and presents unique diagnostic and management challenges.<h4>Case summary</h4>We report two rare cases of DMD coexisting with chromosomal abnormalities, both followed at Siriraj Hospital. The first case involved a 6-year-old boy with DS who presented with incidentally detected elevated serum transaminase levels, calf pseudohypertrophy, and gait difficulty; gene panel testing identified a hemizygous c.3917dup (p.Asp1307Argfs*4) variant in <i>DMD</i>. The second case involved a 6-year-old girl with proximal muscle weakness and calf pseudohypertrophy; genetic studies revealed a heterozygous delins variant in the <i>DMD</i> (p.Ala3041Serfs*69), skewed X-chromosome inactivation, and mosaic TS [45,X(29%)/46,XX].<h4>Conclusion</h4>The coexisting of DMD with DS or TS produces overlapping phenotypes that can complicate diagnosis; careful genetic evaluation and multidisciplinary management are therefore essential.