PracticeUpdate Conference Series - SSIEM 2018

New Phenotype of Muscle Weakness in Classic Infantile Pompe Disease Has Emerged Etiology of this new phenotype is unclear.

O ver a median of 6.0 years, patients with classic infantile Pompe disease who were treated with enzyme replacement therapy, despite improving in proximal muscle strength and function, developed moderate to severe weakness of the dorsiflexors of the feet at an early age. This outcome of a long-term assessment of qualitative motor development and function in 15 patients with classic infantile Pompe disease was reported at SSIEM 2018. E. Poelman, MD, of Erasmus Medical College in Rotterdam, The Netherlands, and colleagues focused the assessment on the development of distal muscle weakness in relation to general motor development. Patients with classic infantile Pompe disease with a follow-up duration of ≥3.0 years who had learned to walk were included. A comprehensive exam- ination of motor function was conducted every 3 months and recorded on video. Qualitative motor development and function were assessed independently by three reviewers using these recordings. Achievement of motor milestones was scored during regular outpatient visits. Median follow-up duration was 6.0 (3.1–18.2) years in 15 patients. Median age at which motor milestones were achieved included the following: ƒ ƒ Sitting: 10.6 (8.3–13.7) months Overall, 5 patients lost the ability to walk and stand, all of whomexhibited proximal weakness of the legs. Early weakness of the foot dorsiflexors was found in 14 patients, which led to foot drop during walking. Weakness of the hands leading to loss of pincer grasp was found in 4 patients, only in patients with general muscle weakness. Dr. Poelman explained that the introduction of enzyme replacement therapy has improved the prospects for patients with classic infantile Pompe disease significantly. The clinical phenotype of patients who survive with enzyme replacement therapy is now ascertained. ƒ ƒ Standing: 12.2 (9.2–16.5) months ƒ ƒ Walking: 17.2 (14.0–21.3) months

Though Pompe disease is known to cause proximal muscle weakness predominantly. Substantial distal weakness was noted to develop in these patients. Dr. Poelman concluded that over a median of 6.0 years, patients with classic infantile Pompe disease treated with enzyme replacement therapy, despite improvement of proximal muscle strength and function, developed moderate to severe weakness of the dorsiflexors of the feet at an early age. A typical phenotype emerged with distal as well as proximal weakness, which differs from patients with nonclassic Pompe disease. The etiology of this new phenotype of muscle weakness is unclear. Further investigation is required. In a related study, Sehnaz Basaran, MD, of Çukurova University in Adana, Turkey, and colleagues evaluated the motor function of 17 patients with infantile Pompe disease. The following tests were performed on 17 patients from a group of 19 mobile patients, as well as on healthy children and patients with Duchenne

muscular dystrophy: ƒ ƒ 6-minute walk test ƒ ƒ Timed 10-m walk test

PRACTICEUPDATE CONFERENCE SERIES • SSIEM 2018 12