Long-term complications in classic galactosemia are not progressive

Classic galactosemia (CG) is a potentially lethal genetic disorder that results from profound deficiency of galactose-1-P uridylyltransferase. Despite early detection and life-long dietary restriction of galactose, which is the current standard of care, many patients with CG grow to experience a range of long-term developmental complications that can include difficulties with speech/voice/language, cognitive, motor, and psychosocial outcomes, among other problems. That these complications are common in CG is well-documented, but whether they are also progressive has been a point of controversy for decades. Here, we addressed the question of whether long-term outcomes in CG are progressive by analyzing a robust data set in each of 4 ways. First, we compared cross-sectional Vineland-3 Adaptive Behavior Scales scores for 101 cases and 65 unaffected sibling controls and found no evidence of consistently declining scores with age. Second, we analyzed longitudinal Vineland-3 subdomain scores for 45 cases and 34 controls to see if individual participants demonstrated developmental gains (positive slope) or losses (negative slope) over time. The changes in most growth scale value (GSV) scores, which are not normed, were positive for both cases and controls <10y, and either positive or near zero for participants ≥10y. In contrast, the slopes of most v-Scale scores, which are normed, were negative for many cases <10y, indicating that these children, while gaining milestones, were gaining them at a slower pace than their counterparts in the reference population. Third, we analyzed medical records from 76 cases, assigning ordinal scores for complications and gathering the quantitative results of relevant formal assessments where available. Both cross-sectional and longitudinal analyses of both ordinal and formal assessment scores confirmed that outcomes were mostly stable, albeit with some ups and downs in isolated cases. Finally, we analyzed data collected via custom family-response surveys from 124 cases and 67 controls regarding each participant's perceived symptom severity over time. Among cases, the percentages of respondents reporting worsening symptoms over time for speech, cognitive, motor, and psychosocial outcomes were 0.8%, 6.6%, 5.2%, and 9.8%, respectively. Among controls, the corresponding percentages were 0.0%, 1.5%, 1.5%, and 6.5%, respectively. These results provide compelling evidence that long-term developmental complications are not progressive for a majority of patients with CG.