Long-Acting Gonadotropin-Releasing Hormone Analogues for Central Precocious Puberty, Including 45-mg 6-month Subcutaneous Leuprolide Acetate: Use for Treatment and Treatment Monitoring.

INTRODUCTION: Studies of gonadotropin-releasing hormone analogues [intramuscular (IM) leuprolide acetate (LA) and triptorelin] for treatment monitoring of central precocious puberty (CPP) demonstrate this approach is effective for confirming pubertal hormone suppression. Herein, we provide new data using subcutaneous LA (SC LA) suggesting similar efficacy for treatment monitoring. METHODS: PubMed, Embase, and CINAHL were searched for studies of GnRHa use to monitor treatment of CPP. The titles and the abstracts were reviewed; five studies were selected. Additionally, new unpublished data for SC LA from the original phase 3 trial (primary data published by Klein et al.) were evaluated. Serum LH and leuprolide levels at screening, 1, 4, and 6 hours after the first dose SC LA were analyzed and plotted. RESULTS: Data from 162 children (155 girls) were evaluated. SC and IM LA produced overlapping median LH concentration curves and peak LH concentrations after the first dose. For IM LA, subsequent doses yielded suppressed peak LH levels (2.7 IU/L [mean]). For SC LA, subsequent doses also resulted in significant suppressed peak LH levels (0.2±0.02 IU/L) and achieved sex-steroid hormone suppression in >98%. CONCLUSIONS: Compared to IM LA and triptorelin, long-acting SC LA shows similar burst kinetics and rapid LH rise after the first dose, followed by similar suppression of LH and sex steroids after subsequent doses. Since IM LA and triptorelin have demonstrated usefulness that is comparable to that of traditional GnRH stimulation testing for monitoring CPP, we presume that SC LA may be similarly employed.

Lectins As Effective Tools in the Study of the Biliary Network and the Parenchymal Architecture of the Zebrafish (Danio rerio) Liver.

Lectins are carbohydrate-binding proteins with specific affinity to glycoconjugates expressed in various tissues. Lectins are of substantial utility as research, histochemical, and diagnostic tools in mammalian systems. Reactivity of 12 commonly used plant-based lectins was studied in zebrafish liver. Four lectins, tomato lectin (TL), wheat germ agglutinin, concanavalin A, and Jacalin showed strong reactivity to hepatic parenchymal structures. Importantly, TL reacted to glycoconjugates within segments of the larval and adult intrahepatic biliary network, from canaliculi to bile ducts. We provide evidence that lectins can serve as important histochemical tools to investigate the structural and functional characteristics of the zebrafish liver.

Novel heterozygous PRPH2 variant identified in a patient with spinocerebellar ataxia type 14 and macular dystrophy.

PURPOSE: To report on a patient with spinocerebellar ataxia type 14 (SCA14) and macular dystrophy with identification of a novel PRPH2 variant. METHODS: Case report. RESULTS: A 63-year-old female with molecularly confirmed SCA14 presented with symmetric pigmentary disturbances in a perifoveal distribution resembling a pattern macular dystrophy. She had no history of using medications with recognized toxic macular effects. Subsequent genetic testing confirmed a novel heterozygous missense variant of unknown significance in PRPH2 (PRPH2: c.694 G>A, p.(Ala232Thr)). CONCLUSIONS: To our knowledge, this is the first case of macular dystrophy identified in a patient with SCA14. While it is possible that the macular dystrophy observed in this patient might be an under-reported phenotype associated with SCA14, the pattern of macular changes is consistent with PRPH2-related disorders. The identified missense variant is predicted to be damaging by most in silico models, and the residue is highly conserved, adding support to a dual genetic diagnosis in this case.

Parental diabetes distress is a stronger predictor of child HbA1c than diabetes device use in school-age children with type 1 diabetes.

INTRODUCTION: Diabetes distress (DD) describes the unrelenting emotional and behavioral challenges of living with, and caring for someone living with, type 1 diabetes (T1D). We investigated associations between parent-reported and child-reported DD, T1D device use, and child glycated hemoglobin (HbA1c) in 157 families of school-age children. RESEARCH DESIGN AND METHODS: Parents completed the Parent Problem Areas in Diabetes-Child (PPAID-C) and children completed the Problem Areas in Diabetes-Child (PAID-C) to assess for DD levels. Parents also completed a demographic form where they reported current insulin pump or continuous glucose monitor (CGM) use (ie, user/non-user). We measured child HbA1c using a valid home kit and central laboratory. We used correlations and linear regression for our analyses. RESULTS: Children were 49% boys and 77.1% non-Hispanic white (child age (mean±SD)=10.2±1.5 years, T1D duration=3.8±2.4 years, HbA1c=7.96±1.62%). Most parents self-identified as mothers (89%) and as married (78%). Parents' mean PPAID-C score was 51.83±16.79 (range: 16-96) and children's mean PAID-C score was 31.59±12.39 (range: 11-66). Higher child HbA1c correlated with non-pump users (r=-0.16, p<0.05), higher PPAID-C scores (r=0.36, p<0.001) and higher PAID-C scores (r=0.24, p<0.001), but there was no association between child HbA1c and CGM use. A regression model predicting child HbA1c based on demographic variables, pump use, and parent-reported and child-reported DD suggested parents' PPAID-C score was the strongest predictor of child HbA1c. CONCLUSIONS: Our analyses suggest parent DD is a strong predictor of child HbA1c and is another modifiable treatment target for lowering child HbA1c.

RPGR: Deep Phenotyping and Genetic Characterization With Findings Specific to the 3'-end of ORF15.

Purpose: To describe a group of patients with retinitis pigmentosa GTPase regulator (RPGR)-related retinopathy with a tapetal-like retinal sheen and corresponding changes in the reflectivity of the ellipsoid zone on optical coherence tomography (OCT) imaging. Methods: A retrospective case series of 66 patients with a disease-causing variant in RPGR was performed. An expert examiner, masked to patient demographics, clinical evaluations, and specific RPGR variant, analyzed color fundus photographs for the presence of a tapetal-like retinal sheen and assessed OCT images for the presence of an abnormally broad hyper-reflective band in the outer retina. Longitudinal reflectivity profiles were generated and compared with healthy controls. Results: Twelve patients (18.2%) had a retinal sheen on color images that cosegregated with an abnormally broad hyper-reflective ellipsoid zone band on OCT imaging. Three-fourths of these patients were male, had a cone-rod dystrophy, and had pathogenic RPGR variants located toward the 3'-end of ORF15. This group had a different longitudinal reflectivity profile signature compared with controls. After a period of prolonged dark adaptation, the abnormal hyper-reflective band on OCT became less apparent, and the outer retinal layers adopted a more normal appearance. Conclusions: RPGR-related retinopathy should be considered for males presenting with retinal sheen, abnormal ellipsoid zone hyper-reflectivity, and cone or cone-rod dysfunction on ERG, and pursued with molecular testing. Our results have implications for understanding the role of the C-terminal domain encoded by RPGR ORF15 in the phototransduction cascade. Further, the findings may be important to incorporate into both inclusion criteria and outcome measure developments in future RPGR-related cone or cone-rod dystrophy clinical trials.

Improved glycemic control either alone, or combined with antioxidant supplementation, fails to restore blood glutathione or markers of oxidative stress in adolescents with poorly controlled type 1 diabetes.

In earlier studies, we showed that adolescents with type 1 diabetes mellitus (T1DM) have significant glutathione (GSH) depletion and that GSH is reciprocally related to glycemic control. In both the general population and in those with diabetes, the use of over-the-counter antioxidant supplements is widespread. We hypothesized that improved glycemic control, alone or in combination with dietary antioxidants, would restore blood GSH pool. The study included 41 participants who were 15.8 ± 2.4 years of age (mean ± standard deviation) and with poorly controlled T1DM (hemoglobin A1c [HbA1c] 8.2 ± 0.6%). Erythrocyte GSH, and 3-nitrotyrosine, F2-isoprostane, and 8-hydroxy-2'-deoxy-guanosine (as markers of protein, lipid, and DNA oxidative stress, respectively) were determined in the postabsorptive state after blood glucose was maintained overnight near euglycemia. Participants were then randomized to a mix of antioxidants (vitamin C, selenium, zinc, vitamin E, ß-carotene) or placebo for 3 to 6 months, and diabetes management was intensified using CSII (n = 30) or multiple daily injections (n = 11) coupled with CDE phone calls and visits with a Nutritionist. A second, identical study was performed when/if a drop in HbA1c ≥0.5% was achieved. HbA1c levels dropped similarly in both groups (from 8.9 ± 1.0% to 7.9 ± 0.9% and 8.5 ± 0.6% to 7.7 ± 0.7% in placebo and antioxidant group, respectively). Neither total nor reduced GSH was altered by improved metabolic control. Markers of protein, lipid, and DNA oxidation remained unaltered. We conclude that, in youngsters with T1DM, neither a significant improvement in diabetes control over a 3-month period nor the regimen of dietary antioxidant supplied in the current study can mitigate oxidative stress. These findings suggest that, in adolescents with T1DM, (1) more sustained improvement of diabetes control may be needed to alleviate oxidative stress and (2) the putative benefit of antioxidant supplements remains to be proven.

Infant and Maternal Vitamin D Supplementation: Clinician Perspectives and Practices.

INTRODUCTION: Rates of infant vitamin D supplementation fall short of guideline recommendations. We explored this discrepancy from the clinician perspective as they advise and affect this important intervention to prevent rickets. We compared infant and high-dose maternal vitamin D supplementation prescribing attitudes and practices between infant-only clinicians (IC) and clinicians who care for mothers and infants (MIC). METHODS: We surveyed clinicians in departments of family medicine, obstetrics/gynecology, primary care pediatrics, neonatology, newborn nursery, and members of vitamin D and rickets working groups and a social media group for lactation medicine providers about their perspectives and practices regarding vitamin D supplementation. RESULTS: 360 clinician survey responses were analyzed. In current practice, IC were more likely than MIC to recommend vitamin D supplementation to exclusively (P < .001) and partially breastfed infants (P = .005). MIC were more likely than IC to discuss infant and high-dose maternal supplementation options and let the parents/caregivers choose (34.7%, 22.0%, P = .009). If supplementing the mother with high-dose vitamin D or the infant directly each provided adequate vitamin D in the infant, MIC were more likely than IC to think that supplementation of the mother would be preferred by parents/caregivers (63.0%, 45.2%, P = .003), improve adherence (66.5%, 49.4%, P = .006), and promote breastfeeding (54.7%, 36.5%, P = .001); they were also more likely to recommend supplementation of the mother (17.7%, 8.9%, P = .04). CONCLUSIONS: MIC are more likely than IC to embrace high-dose maternal vitamin D supplementation to provide adequate vitamin D for infants. This highlights an opportunity for further education of clinicians about this option.

Central retinal artery occlusion: a retrospective study of disease presentation, treatment, and outcomes.

OBJECTIVE: A central retinal artery occlusion (CRAO) represents a form of ocular stroke with poor visual prognosis. CRAO shares a common pathophysiology with cerebral ischemic stroke but presents unique diagnostic and management challenges leading to variability in clinical practice. This study aims to assess the presentation, treatment, and outcomes of CRAO at a tertiary care centre in Canada over 2 years and elucidate potential areas for improvement in the care of these patients. METHODS: Single-institution retrospective review including 27 patients diagnosed with CRAO from March 2018 to March 2020 in Edmonton, Alberta. RESULTS: Most patients with CRAO presented to eye care providers (14 of 27); others presented to the emergency department (10 of 27) or family physicians (2 of 27). Three patients (11.1%) presented within 4.5 hours of symptom onset. At presentation, 81% of patients had visual acuity of 20/400 or worse in the affected eye. No patients received thrombolysis. The majority of CRAO cases had a nonarteritic etiology (92.6%). All patients had at least one pre-existing vascular risk factor. Forty-eight percent of patients received escalated medical therapy. Ipsilateral carotid stenosis was identified in 5 patients (18.5%); 3 patients required carotid endarterectomy. Two patients were diagnosed with atrial fibrillation. Two patients experienced symptomatic cerebral ischemia within 6 weeks of CRAO. CONCLUSIONS: The majority of patients with CRAO presented to eye care providers, and few present within the potential window for thrombolysis of 4.5 hours, highlighting the need for public awareness strategies. Our cohort highlights the significant rate of systemic comorbidity that exists in these patients.

Ten-year analysis of traumatic open-globe injuries in Edmonton, Canada, from 2009-2018.

OBJECTIVE: To identify and characterize the incidence and correlates of open-globe injuries documented at the Eye Institute of Alberta (EIA) at the Royal Alexandra Hospital in Edmonton. DESIGN: A 10-year single-centre retrospective chart review. METHODS: All patients who underwent traumatic open-globe injury repair at EIA from January 2009-December 2018 were identified using key search terms. Charts were individually assessed for key demographic variables, including mechanism and location of injury. Patterns in open-globe injury incidence over the 10-year period and across demographics were assessed using Poisson regression. Associations between key demographic variables also were analyzed. RESULTS: In total, 551 traumatic open-globe injuries were treated at the EIA from January 2009-December 2018, resulting in an average of 4.63 injuries per month over the 10-year period. Mean patient age was 42 ± 21.56 years. The number of males (n = 442) presenting for open-globe injury repair was 3.9 times higher than that for females (n = 114). Among patients for whom use of eye protection was recorded (n = 186), only 11% reported using eye protection at the time of the trauma. The incidence rate of injuries with zone 3 involvement was significantly higher in males (41.4%) than in females (29.8%). CONCLUSION: Open-globe injuries remain a significant source of ocular morbidity at EIA, averaging just over 1 emergency case a week. Given the strong association with sex and the infrequent use of eye protection, targeted public health strategies are necessary to mitigate the risk of these sight-threatening injuries.

Misfolding of fukutin-related protein (FKRP) variants in congenital and limb girdle muscular dystrophies.

Fukutin-related protein (FKRP, MIM ID 606596) variants cause a range of muscular dystrophies associated with hypo-glycosylation of the matrix receptor, α-dystroglycan. These disorders are almost exclusively caused by homozygous or compound heterozygous missense variants in the FKRP gene that encodes a ribitol phosphotransferase. To understand how seemingly diverse FKRP missense mutations may contribute to disease, we examined the synthesis, intracellular dynamics, and structural consequences of a panel of missense mutations that encompass the disease spectrum. Under non-reducing electrophoresis conditions, wild type FKRP appears to be monomeric whereas disease-causing FKRP mutants migrate as high molecular weight, disulfide-bonded aggregates. These results were recapitulated using cysteine-scanning mutagenesis suggesting that abnormal disulfide bonding may perturb FKRP folding. Using fluorescence recovery after photobleaching, we found that the intracellular mobility of most FKRP mutants in ATP-depleted cells is dramatically reduced but can, in most cases, be rescued with reducing agents. Mass spectrometry showed that wild type and mutant FKRP differentially associate with several endoplasmic reticulum (ER)-resident chaperones. Finally, structural modelling revealed that disease-associated FKRP missense variants affected the local environment of the protein in small but significant ways. These data demonstrate that protein misfolding contributes to the molecular pathophysiology of FKRP-deficient muscular dystrophies and suggest that molecules that rescue this folding defect could be used to treat these disorders.

Evolution of focal choroidal excavation in ABCA4-related retinopathy.

Purpose: To report long-term evolution of unilateral focal choroidal excavation in a patient with ABCA4-related retinopathy. Observations: A 51-year-old female with ABCA4-related retinopathy developed a small juxtafoveal defect in Bruch's membrane in a region of macular atrophy in her left eye. In follow-up, the defect widened and subsequently developed into a focal choroidal excavation. Over the next 8 years, serial optical coherence tomography imaging illustrated the conversion of the focal choroidal excavation from conforming subtype into non-conforming subtype with eventual macular hole formation. Conclusions and importance: The long-term follow-up of a patient with serial imaging highlights the potential dynamic nature of focal choroidal excavation in ABCA4-related retinopathy. Progressive retinal degeneration may influence focal choroidal excavation morphology and may promote macular hole formation.

Immediate Higher-Dose Prothrombin Complex Concentrate Without Fresh Frozen Plasma or Fibrinogen Concentrate for Significant Coagulopathic Cardiac Surgical Field Bleeding.

BACKGROUND: Treatment of significant coagulopathic cardiac surgical field bleeding with immediate higher-dose prothrombin complex concentrate (PCC) without fresh frozen plasma (FFP) or fibrinogen concentrate is unexplored. AIMS: To study characteristics, chest drainage, and clinical outcomes of patients with significant coagulopathic surgical field bleeding treated with immediate higher-dose (defined at >15 IU/kg based on factor IX) PCC without FFP or fibrinogen concentrate. METHODS: We screened sequential cardiac surgery patients. We reviewed electronic blood bank data, Australian Society of Cardiothoracic Surgery database information and anaesthetic, intensive care unit (ICU), ward and radiological charts and electronic data. We identified patients deemed by the operating surgeon to require treatment for significant coagulopathic surgical field bleeding who underwent immediate higher-dose PCC without FFP or fibrinogen concentrate. RESULTS: Among 168 patients, we identified 30 who underwent immediate higher-dose PCC without FFP or fibrinogen concentrate. Median age was 68 years, 23 were male, 17 underwent coronary artery bypass surgery and three underwent complex surgery (David procedure, redo mitral valve surgery, and redo thoraco-abdominal aneurysm repair). Median dose of PCC was 2,500 IU. In addition, 27% underwent platelets and one underwent cryoprecipitate. Chest drainage at 24 hours was 505 ml. Survival to hospital discharge was 100%. There were no cases of pulmonary embolism, stroke, or other thrombotic events. Stage 1 AKI occurred in one patient. CONCLUSION: In a pilot cohort of patients with significant coagulopathic surgical field bleeding, immediate higher-dose PCC without FFP or fibrinogen concentrate was feasible and had an acceptable efficacy and safety profile, which justifies future controlled studies.

Remedy to Diabetes Distress (R2D2): Development protocol for a scalable screen-to-treat program for families of school-age children.

BACKGROUND: School-age children with type 1 diabetes (T1D) need help from parents or other adult caregivers (caregivers) to effectively manage T1D, resulting in greater vulnerability to Diabetes Distress (DD) for both children and caregivers. Unfortunately, there are no scalable screen-to-treat programs for clinics to adopt to identify and treat DD in school-age families. METHODS AND ANALYSES: We aim to design a scalable, clinic-based screen-to-treat program for DD in families of school-age children and to test whether our new program to reduce caregiver and child DD also reduces child glycemic levels. Our Remedy to Diabetes Distress (R2D2) program will target caregivers and children with T1D who are between 8 and 12 years old. It will merge routine and automated surveillance of DD in the clinical setting with at home digital delivery of a theory-based behavioral and psychological treatment of DD. We will use the ORBIT Model for Behavioral Intervention development to guide four small and cost-effective formative studies to develop our R2D2 program and assess initial treatment effects. In tandem, we will implement clinic-based DD screening in school-age families and assess feasibility and acceptability of our screening platform as a Quality Improvement activity. The study started in September 2020 and is scheduled to conclude in 2025. CONCLUSIONS: The study will use a single Institutional Review Board (IRB) with Children's Mercy-Kansas City operating as the IRB of record. We will disseminate study results through presentations at scientific conferences and through peer-reviewed journals read by the psychology and diabetes care communities.

BMP3 is a novel locus involved in the causality of ocular coloboma.

Coloboma, a congenital disorder characterized by gaps in ocular tissues, is caused when the choroid fissure fails to close during embryonic development. Several loci have been associated with coloboma, but these represent less than 40% of those that are involved with this disease. Here, we describe a novel coloboma-causing locus, BMP3. Whole exome sequencing and Sanger sequencing of patients with coloboma identified three variants in BMP3, two of which are predicted to be disease causing. Consistent with this, bmp3 mutant zebrafish have aberrant fissure closure. bmp3 is expressed in the ventral head mesenchyme and regulates phosphorylated Smad3 in a population of cells adjacent to the choroid fissure. Furthermore, mutations in bmp3 sensitize embryos to Smad3 inhibitor treatment resulting in open choroid fissures. Micro CT scans and Alcian blue staining of zebrafish demonstrate that mutations in bmp3 cause midface hypoplasia, suggesting that bmp3 regulates cranial neural crest cells. Consistent with this, we see active Smad3 in a population of periocular neural crest cells, and bmp3 mutant zebrafish have reduced neural crest cells in the choroid fissure. Taken together, these data suggest that Bmp3 controls Smad3 phosphorylation in neural crest cells to regulate early craniofacial and ocular development.

Critical Care Transport of the Temporary Portable Ventricular Support Device.

OBJECTIVE: Cardiogenic shock is a critical emergency for which ventricular support devices (VSDs), such as the Impella (AbioMed Inc, Danvers, MA), are placed. Many referring facilities cannot provide cardiac intensive care. This requires a regional approach to the care of patients with VSD. Critical care transport to the regional center is needed and requires specialty trained personnel. As the need for specialty trained personnel increases, appropriate utilization of the personnel needs to be considered. This study illustrates the effective transport and successful management of Impella patients in the transport environment by a downsized specialty trained critical care team. METHODS: A retrospective chart review explored critical care transports of patients with Impella devices over a 73-month period. Our goal was to show that with training, protocols, and guidelines a downsized critical care team can effectively transport these high-risk, low-frequency patients. RESULTS: Forty-seven VSD transports occurred within 13,823 transports during the study period. Twenty-seven included an Impella device only. Thirteen were completed by a downsized team. One hundred percent of the transport resulted in the patient having perfusing rhythms and blood pressures at the receiving facility. CONCLUSION: VSDs can be successfully transported between hospitals with small specialty trained critical care transport teams using air or ground assets.

A Potent and Selective Kallikrein-5 Inhibitor Delivers High Pharmacological Activity in Skin from Patients with Netherton Syndrome.

Regulation of proteolytic activity in the skin plays a pivotal role in epidermal homeostasis. This is best exemplified in Netherton syndrome, a severe genetic skin condition caused by loss-of-function mutations in the gene serine protease inhibitor Kazal-type 5 encoding lympho-epithelial Kazal-type-related inhibitor, a serine protease inhibitor that regulates kallikrein (KLK)-related peptidase 5, 7, and 14 activities. KLK5 plays a central role in stratum corneum shedding and inflammatory cell signaling, activates KLK7 and KLK14, and is therefore an optimal therapeutic target. We aimed to identify a potent and selective small-molecule inhibitor of KLK5 amenable to epidermal delivery. GSK951 was identified using a structure-based design strategy and showed a half maximal inhibitory concentration of 250 pM for KLK5 and greater than 100-fold selectivity over KLK7 and KLK14. Cocrystal structure analysis identified the critical catalytic site interactions to a surrogate for KLK5. Topical application of GSK951-containing cream inhibited KLK5 activity in TgKLK5 mouse skin, reduced transepidermal water loss, and decreased proinflammatory cytokine expression. GSK951 achieved high concentrations in healthy human epidermis following topical application in a cream formulation. Finally, KLK5 protease activity was increased in stratum corneum of patients with Netherton syndrome and significantly inhibited by GSK951. These findings unveil a KLK5-specific small-molecule inhibitor with a high therapeutic potential for patients with Netherton syndrome.

PEX6 Mutations in Peroxisomal Biogenesis Disorders: An Usher Syndrome Mimic.

Purpose: Peroxisomal biogenesis disorders (PBDs) represent a spectrum of conditions that result in vision loss, sensorineural hearing loss, neurologic dysfunction, and other abnormalities resulting from aberrant peroxisomal function caused by mutations in PEX genes. With no treatments currently available, we sought to investigate the disease mechanism in a patient with a PBD caused by defects in PEX6 and to probe whether overexpression of PEX6 could restore peroxisome function and potentially offer therapeutic benefit. Design: Laboratory-based study. Participants: A 12-year-old boy sought treatment with hearing loss and retinopathy. After negative results in an Usher syndrome panel, targeted genetic testing revealed compound heterozygous mutations in PEX6. These included a 14-nucleotide deletion (c.802_815del: p.(Asp268Cysfs∗8)) and a milder missense variant (c.35T→C:(p.Phe12Ser)). Methods: Patient-derived skin fibroblasts were cultured, and a PEX6 knockout cell line was developed using clustered regularly interspaced short palindromic repeats and Cas9 technology in HEK293T cells to emulate a more severe disease phenotype. Immunoblot analysis of whole cell lysates was performed to assess peroxisome number. Immunofluorescence studies used antibodies against components of the peroxisomal protein import pathway to interrogate the effects of mutations in PEX6 on protein trafficking. Main Outcome Measures: Primary outcome measures were peroxisome abundance and matrix protein import. Results: Peroxisome number was not significantly different between control fibroblasts and patient fibroblasts; however, fewer peroxisomes were observed in PEX6 knockout cells compared with wild-type cells (P = 0.04). Analysis by immunofluorescent microscopy showed significantly impaired peroxisomal targeting signal 1- and peroxisomal targeting signal 2-mediated matrix protein import in both patient fibroblasts and PEX6 knockout cells. Overexpressing PEX6 resulted in improved matrix protein import in PEX6 knockout cells. Conclusions: Mutations in PEX6 were responsible for combined hearing loss and retinopathy in our patient. The primary peroxisomal defect in our patient's skin fibroblasts was impaired peroxisomal protein import as opposed to reduction in the number of peroxisomes. Genetic strategies that introduce wild-type PEX6 into cells deficient in PEX6 protein show promise in restoring peroxisome function. Future studies of patient-specific induced pluripotent stem cell-derived retinal pigment epithelium cells may clarify the role of PEX6 in the retina and the potential for gene therapy in these patients.