Hypophosphatasia and collagen VI-related muscular dystrophy presenting with gait disturbance and recurrent fractures.

Proximal muscle weakness is a recognized feature of hypophosphatasia (HPP), although significant structural muscle pathology is not typically observed. We report a 48-year-old woman with a 20-year history of progressive gait disturbance, proximal muscle weakness (Medical Research Council grade 2-4), and recurrent low-trauma fractures. Laboratory evaluation revealed persistently low serum alkaline phosphatase, and genetic testing identified a heterozygous likely pathogenic variant in ALPL (NM_000478.6:c.1559del; p.[Leu520Argfs*86]), confirming the diagnosis of HPP. However, severe muscle weakness and extensive fatty infiltration on muscle magnetic resonance imaging were disproportionate to what would be expected from HPP alone, prompting further evaluation. Additional genetic analysis identified a previously unreported homozygous intronic deletion in COL6A2 (NM_001849.4:c.1771-18_1771-3del), classified as likely pathogenic and predicted to affect splicing with uncertain protein consequences, confirming concurrent collagen VI-related muscular dystrophy (COL6-RD). Family genetic testing identified the same ALPL variant in the proband's 16-year-old daughter, who was subsequently diagnosed with HPP and found to be a carrier of COL6-RD. This case highlights that HPP and muscular dystrophy can coexist and underscores the importance of comprehensive neuromuscular evaluation when muscle weakness is present in patients with HPP.