Christy H. Smith

While diagnostic disparities by race and age of onset are reported in inherited retinal diseases, their impact on Stargardt disease (STGD)-a clinically and genetically heterogeneous macular dystrophy-remains unclear. We analyzed 246 STGD patients at a U.S. referral center (2003-2024) who completed genetic testing, comparing laboratory-reported results (lab-GT) with manual, phenotype-integrated reinterpretation (m-GT) of ABCA4 sequencing incorporating updated variant databases and genotype-phenotype correlation. Diagnostic yield and variant burden were assessed by race and age of onset. Positive/likely positive (P/LP) lab-GT was identified in 79% (195), with 78% (191) attributable to ABCA4 (ABCA4-positive lab-GT: 57% [141]). M-GT increased ABCA4-P/LP yield to 91% (224). Black participants had lower ABCA4-positive lab-GT than White participants (55% vs. 73%) and fewer pathogenic variants; on multivariable analysis, Black race (OR 0.34) and later age of onset (OR 0.95/year) independently predicted reduced molecular diagnosis. The disparity by race resolved with P/LP m-GT (89% vs. 90%); by age of onset, yield remained lower in late-onset cases (ABCA4-P/LP lab-GT: 86% early- [≤10 yrs], 83% intermediate- [11-44 yrs], 54% late-onset [≥45 yrs], improving to 97%, 94%, and 77% after m-GT). Posttest reinterpretation improves diagnostic yield, particularly for Black and late-onset STGD patients, underscoring the value of ancestry-informed interpretation, historical reanalysis, and genotype-phenotype correlation.

Sorbitol dehydrogenase (SORD) deficiency, due to biallelic loss-of-function variants in the SORD gene, is a recently recognized cause of autosomal recessive hereditary neuropathy. Specific diagnosis is difficult on clinical grounds alone, and molecular genetic testing of SORD is complicated by the presence of a pseudogene. Biochemical testing of serum sorbitol is suggested as a potential biomarker. We report a novel urine biochemical profile of elevated excretion of sorbitol and a second polyol, xylitol, to aid in the identification of individuals with SORD-related neuropathy. Patients with confirmed or suspected SORD-related neuropathy were recruited by clinicians from 7 academic medical centers and 1 nonprofit specialty care center. Urine was analyzed by a clinically validated, gas chromatography-mass spectrometry assay to measure sorbitol and xylitol excretion. Over 700 reference samples were evaluated from residual clinical samples. Clinical and molecular findings were gathered using a standardized questionnaire. Nineteen individuals with a clinical and genetic diagnosis of SORD-related neuropathy (median age 31 years, 47% female) and 715 reference samples were used to determine the initial performance of this index urine test. The median sorbitol excretion in affected individuals was 638 mmol/mol creatinine (1st percentile of disease range = 456; reference median = 7, reference 99th percentile = 198). The median xylitol excretion was 1,577 mmol/mol creatinine (1st percentile of disease range = 1,242; reference median = 7, reference 99th percentile = 102). In this patient cohort, the combination of sorbitol and xylitol yielded 100% sensitivity and specificity for SORD-related neuropathy. Four additional individuals who had clinical phenotypes compatible with SORD-related neuropathy had abnormal urine sorbitol/xylitol profile, 2 with genotypes involving a variant of unknown significance in SORD and 2 with a single heterozygous pathogenic SORD variant detected, whereas normal urine sorbitol/xylitol levels were observed in 11 asymptomatic, heterozygous carriers. These data demonstrate the clinical utility of urine sorbitol and xylitol analysis in the screening and diagnosis of SORD deficiency-related neuropathy. In addition, this is the first description of elevated xylitol in SORD deficiency as a clinically informative biomarker, which may increase the specificity of biochemical testing.

: While diagnostic disparities by race and age of onset are reported in inherited retinal diseases, their impact on Stargardt disease (STGD)—a clinically and genetically heterogeneous macular dystrophy—remains unclear. We analyzed 246 STGD patients at a U.S. referral center (2003-2024) who completed genetic testing, comparing laboratory-reported results (lab-GT) with manual, phenotype-integrated reinterpretation (m-GT) of ABCA4 sequencing incorporating updated variant databases and genotype-phenotype correlation. Diagnostic yield and variant burden were assessed by race and age of onset. Positive/likely positive (P/LP) lab-GT was identified in 79% (195), with 78% (191) attributable to ABCA4 ( ABCA4- positive lab-GT: 57% [141]). M-GT increased ABCA4- P/LP yield to 91% (224). Black participants had lower ABCA4- positive lab-GT than Whites (55% vs. 73%) and fewer pathogenic variants; on multivariable analysis, Black race (OR 0.34) and later age of onset (OR 0.95/year) independently predicted reduced molecular diagnosis. The disparity by race resolved with P/LP m-GT (89% vs. 90%); by age of onset, yield remained lower in late-onset cases ( ABCA4- P/LP lab-GT: 86% early-[≤10yrs], 83% intermediate-[11-44yrs], 54% late-onset [≥45yrs], improving to 97%, 94%, and 77% after m-GT). Post-test reinterpretation improves diagnostic yield, particularly for Black and late-onset STGD patients, underscoring the value of ancestry-informed interpretation, historical reanalysis, and genotype-phenotype correlation.

Importance: Multiple clinical trials for Stargardt disease are ongoing, as there is no treatment available for this condition. However, timely recruitment of clinical trial participants remains challenging, risking incomplete study cohorts and prolonged study timelines that together escalate the possibility of trial failure. Factors associated with clinical trial participation in Stargardt are poorly understood. Identifying drivers of clinical trial participation and genetic testing completion may improve trial design and access. Objective: To identify demographic and clinical factors associated with clinical trial participation and genetic testing completion in Stargardt. Design: Retrospective cohort study of patients seen at a genetic eye disease center from January 2003 to December 2024. Associations were evaluated using bivariate analysis and multivariable logistic regression. Setting: Single-center study at a tertiary referral center. Participants: 280 patients clinically diagnosed with Stargardt disease [median (IQR) age at presentation 37 (20-52) years; follow-up 4.5 (1.6-10.1) years]. Exposures: Demographic and clinical factors, including race, insurance, education, employment, parenting status, age of onset, and genetic counseling history. Main Outcomes and Measures: Genetic testing completion (all participants) and clinical trial participation (among ABCA4- positive participants). Results: Among 280 participants, 246 (88%) completed genetic testing. Among 223 ABCA4 -positive participants, 45 (20%) had enrolled in a clinical trial. Clinical trial participation was associated with later onset [≥60 years; OR (95% CI) 36.7 (2.5-537.1)], part-time employment [9.3 (1.01-172.9)], and was less likely among retired individuals [0.014 (0.0005-0.4)] or those without genetic counseling [0.22 (0.07-0.71)]. In multivariable analysis, genetic testing completion was less likely in participants who were Black [0.40 (0.16-0.98)], under/uninsured [0.47 (0.19-0.97)], without genetic counseling [0.09 (0.03-0.22)], or not planning to have children [0.35 (0.14-0.89)]. Common reasons for non-completion included loss to follow-up, refusal, and awaiting genetic counseling. Conclusions and Relevance: In this large single-center cohort, one in five participants with molecularly confirmed Stargardt had enrolled in a clinical trial. Older age of onset, part-time employment, and genetic counseling may promote clinical trial participation among Stargardt patients, while retirement may be negatively associated. These findings may ultimately support the development of rational strategies to accelerate clinical trial enrollment, thereby broadly supporting the development of effective treatments for Stargardt disease.

Objective: To identify clinical and demographic predictors of genetic testing (GT) completion and diagnostic yield among patients with genetic eye disorders (GED) at a large U.S. tertiary academic center. Design: Retrospective cohort study. Participants: Patients with clinically diagnosed GEDs evaluated at the Wilmer Eye Institute’s Genetic Eye Disease (GEDi) Center between 2002 and 2025. Methods: Demographic, clinical, and GT data were extracted. Bivariate analyses and multivariable logistic regression identified factors associated with GT completion and molecular diagnosis. Subgroup analyses examined racial disparities between Black, non-Hispanic White, and Other race participants. Main Outcome Measures: Proportion of patients completing GT, molecular diagnostic yield, and clinical/demographic predictors of each. Results: Of 1466 participants (median age at presentation 44 years, symptom onset 28 years; median follow-up 6 years), 74% (1088) completed genetic testing, with a likely molecular diagnosis achieved in 62%, inconclusive results in 22%, and no diagnosis in 16%. GT completion was more likely among younger participants with earlier symptom onset, and longer follow-up. Likely molecular diagnosis was more likely in participants with earlier symptom onset, worse visual acuity (VA), male sex, and syndromic or X-linked phenotypes. Black and Other race participants had significantly lower odds of completing GT (Black: OR [95% CI] 0.40 [0.30-0.53]; Other: 0.57 [0.36-0.92]) and receiving a likely molecular diagnosis (Black: 0.37 [0.26-0.51]; Other: 0.58 [0.35-0.98]), and consistently exhibited worse VA at both baseline and follow-up. Notably, among Black and Other race participants, disparities in GT completion and visual outcomes persisted despite equivalent or shorter time from presentation to GT completion, suggesting barriers arise independently of delays in care engagement. We identified 118 causative genes among participants with likely molecular diagnoses, with ABCA4 , USH2A , PRPH2 , RHO , and BEST1 accounting for 47% of cases. Conclusions: This is the largest single-center GED genetic testing cohort reported in the U.S. and reveals significant disparities in GT completion and yield by race, age, sex, and disease-level factors. Our findings underscore the need to expand early access to GT, diversify genomic databases, and address systemic barriers to ensure equity in GED diagnosis, clinical trial access, and delivery of emerging therapies.