Urine protein/osmolality and creatinine/osmolality ratios for assessing proteinuria and motor function in children with spinal muscular atrophy.

BACKGROUND

Spinal muscular atrophy (SMA) is characterized by the degeneration of anterior horn motor neurons. While nusinersen has altered the natural course of SMA, it may accumulate in the kidneys, leading to proteinuria. Therefore, routine pre-dose urine monitoring for proteinuria is recommended. To address this issue, we aimed to evaluate the urinary protein-to-osmolality ratio (UPr/Osm). We also aimed to evaluate the relation of urinary creatinine-to-osmolality ratio (UCr/Osm) to motor function scores.

METHODS

A retrospective study was performed on 42 SMA patients. UPr/Cr, UPr/Osm, and UCr/Osm ratios were calculated. UPr/Cr and UPr/Osm were compared for the presence of proteinuria, while correlation analysis between UCr/Osm and motor scores was performed using CHOP INTEND in patients aged 0-2 years and HFMSE separately in the 2-6 years, 6-12 years, and > 12 years age groups. Furthermore, laboratory parameters were compared between ambulatory and non-ambulatory patients.

RESULTS

The cohort included 17 patients with SMA type 1, 18 with type 2, and 7 with type 3. Proteinuria was detected in 35 (83%) patients using UPr/Cr, whereas only 4 (10%) or 9 (21%) patients had proteinuria with respect to different UPr/Osm cut-offs defined in the literature. UCr/Osm was significantly higher in ambulatory patients. On the other hand, UCr/Osm was correlated with HFMSE scores in the older age groups (6-12 years and > 12 years) (r = 0.553, p = 0.033; r = 0.717, p = 0.02).

CONCLUSIONS

The UPr/Osm test may be a reliable alternative for assessing proteinuria in patients with SMA. UCr/Osm may also be associated with motor function in patients with later-stage SMA.