Grip strength in patients with galactosemia and in a galactose-1-phosphate uridylyltransferase (GALT)-null rat model

Classic galactosemia (CG) and clinical variant galactosemia (CVG) are allelic inborn errors of metabolism that result from profound deficiency, and near-profound deficiency, respectively, of galactose-1-P uridylyltransferase (GALT). Despite early detection and lifelong dietary restriction of galactose, which is the current standard of care, most patients with CG/CVG grow to experience a range of long-term developmental and other complications. One of the less well-understood complications of CG/CVG is decreased hand grip strength, as reported by Potter et al. (2013). Here, we confirm this phenotype in an independent cohort of 36 cases (4-18 years) and 19 controls (4-17 years), and further demonstrate that the grip strength deficit observed in cases may be secondary to growth delay. Specifically, we found that when grip strength of cases and controls in a new cohort recruited in 2022 was plotted by weight, rather than age, the difference between cases and controls for both sexes disappeared. Reanalyzing data from the original 2013 cohort, we found that differences in weight accounted for grip strength differences between cases and controls in girls and young women, but not in boys and young men. Finally, we tested whether a GALT-null rat model of CG also showed a grip strength deficit-it did-and again the difference between GALT-null and wild-type rats associated with differences in body mass. Combined, these results confirm that GALT deficiency is associated with a grip strength deficit in both young patients with CG/CVG and GALT-null rats, and further demonstrate that this phenotype may be secondary to growth delay, and therefore not evidence of a muscle abnormality.