Patient-Specific Induced Pluripotent Stem Cell-Derived RPE Cells: Understanding the Pathogenesis of Retinopathy in Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency.

PURPOSE: Retinopathy is an important manifestation of trifunctional protein (TFP) deficiencies but not of other defects of fatty acid oxidation. The common homozygous mutation in the TFP α-subunit gene HADHA (hydroxyacyl-CoA dehydrogenase), c.1528G>C, affects the long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) activity of TFP and blindness in infancy. The pathogenesis of the retinopathy is unknown. This study aimed to utilize human induced pluripotent stem cell (hiPSC) technology to create a disease model for the disorder, and to derive clues for retinopathy pathogenesis. METHODS: We implemented hiPSC technology to generate LCHAD deficiency (LCHADD) patient-specific retinal pigment epithelial (RPE) monolayers. These patient and control RPEs were extensively characterized for function and structure, as well as for lipid composition by mass spectrometry. RESULTS: The hiPSC-derived RPE monolayers of patients and controls were functional, as they both were able to phagocytose the photoreceptor outer segments in vitro. Interestingly, the patient RPEs had intense cytoplasmic neutral lipid accumulation, and lipidomic analysis revealed an increased triglyceride accumulation. Further, patient RPEs were small and irregular in shape, and their tight junctions were disorganized. Their ultrastructure showed decreased pigmentation, few melanosomes, and more melanolysosomes. CONCLUSIONS: We demonstrate that the RPE cell model reveals novel early pathogenic changes in LCHADD retinopathy, with robust lipid accumulation, inefficient pigmentation that is evident soon after differentiation, and a defect in forming tight junctions inducing apoptosis. We propose that LCHADD-RPEs are an important model for mitochondrial TFP retinopathy, and that their early pathogenic changes contribute to infantile blindness of LCHADD.

Malonyl-CoA decarboxylase deficiency: long-term follow-up of a patient new clinical features and novel mutations.

BACKGROUND: Malonyl-CoA decarboxylase (MLYCD, EC 4.1.1.9) deficiency is a rare autosomal recessive disorder that is widely diagnosed by neonatal screening. METHODS: We report long term follow up of a patient with MLYCD deficiency showing signs of neonatal hypoglycemia, mental retardation, developmental delay and rheumatoid arthritis. Brain MRI revealed patchy, symmetrical hyperintensity of the deep white matter with periventricular white matter and subcortical arcuate fibers being spared. MLCYD gene sequence analysis was done to identify possible mutations. Expression analyses at mRNA and protein levels were also performed. Further, immunocytochemical studies were implemented to check for its subcellular localization. RESULTS: MLYCD gene sequencing identified a novel compound heterozygous mutation (c.22 T>A, p.M1K, c.454 C>A; pH152N) in our patient and a heterozygous mutation in the healthy mother c.22 T>A; pM1K. Reduced expression of RNA and protein levels was observed. Immunocytochemical analysis showed diffused staining across the cytoplasm with apparent signs of intracellular mislocalization to the nucleus. RESULTS also indicated subcellular colocalization of MLCYD with mitochondria was scant compared to control. CONCLUSION: Our patient was identified with a novel compound heterozygous MLYCD mutation at the N-terminal helical domain. This study indicates that protein mislocalization is a characteristic feature of MLYCD deficiency in our patient.

Carrier frequency of a common mutation of carnitine palmitoyltransferase 1A deficiency and long-term follow-up in Finland.

OBJECTIVE: To assess the long-term clinical course of carnitine palmitoyltransferase 1A (CPT1A) deficiency, caused by the c.1364A>C (p.K455T) mutation, and the carrier frequency of this mutation in Finland. STUDY DESIGN: This was a long-term follow-up of patients in whom the common mutation was detected. RESULTS: Between 1999 and 2010, 6 cases of CPT1A deficiency were diagnosed and treated with a high-carbohydrate, low-fat diet. The patients experienced their first symptoms during the first years of life, provoked by viral illness and/or fasting. The clinical features included hypoketotic hypoglycemia, hepatopathy, and loss of consciousness, ranging from transient unconsciousness to prolonged hyperlipidemic coma. Five cases carried a homozygous c.1364A>C (p.K455T) mutation, whereas 1 case had a compound c.1364A>C/c.1493A>C (p.Y498S) mutation. During dietary therapy, the patients had few transient decompensations. No carriers of mutation c.1364A>C were detected by minisequencing of 150 control samples. CONCLUSION: Even though CPT1A deficiency may be life-threatening and lead to prolonged coma, the long-term prognosis is good. A genotype-phenotype correlation implies that the mutations detected are disease-causing. Despite Finland's location close to the Arctic polar region, the carrier frequency of the c.1364A>C mutation in Finland is far lower than that of the variants found in Alaskan, Canadian, and Greenland native populations.