Juvenile cobalamin deficiency in a 17-year-old child with autonomic dysfunction and skin changes

Blood biomarkers for assessment of mitochondrial dysfunction: An expert review

Although mitochondrial dysfunction is the known cause of primary mitochondrial disease, mitochondrial dysfunction is often difficult to measure and prove, especially when biopsies of affected tissue are not available. In order to identify blood biomarkers of mitochondrial dysfunction, we reviewed studies that measured blood biomarkers in genetically, clinically or biochemically confirmed primary mitochondrial disease patients. In this way, we were certain that there was an underlying mitochondrial dysfunction which could validate the biomarker. We found biomarkers of three classes: 1) functional markers measured in blood cells, 2) biochemical markers of serum/plasma and 3) DNA markers. While none of the reviewed single biomarkers may perfectly reveal all underlying mitochondrial dysfunction, combining biomarkers that cover different aspects of mitochondrial impairment probably is a good strategy. This biomarker panel may assist in the diagnosis of primary mitochondrial disease patients. As mitochondrial dysfunction may also play a significant role in the pathophysiology of multifactorial disorders such as Alzheimer's disease and glaucoma, the panel may serve to assess mitochondrial dysfunction in complex multifactorial diseases as well and enable selection of patients who could benefit from therapies targeting mitochondria.

Focal Segmental Glomerulosclerosis Associated with Chronic Progressive External Ophthalmoplegia and Mitochondrial DNA A3243G Mutation

Focal segmental glomerulosclerosis (FSGS) is caused by various etiologies, with mitochondrial dysfunction being one of the causes. FSGS is known to be associated with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), which is a subclass of mitochondrial disease. However, it has rarely been reported in other mitochondrial disease subclasses. Here, we reported a 20-year-old man diagnosed with FSGS associated with chronic progressive external ophthalmoplegia (CPEO) due to mitochondrial DNA (mtDNA) 3243A>G mutation. He presented with left ptosis, short stature, mild sensorineural deafness, and cardiac conduction block. A renal biopsy sample showed segmental sclerosis and adhesions between capillaries and Bowman's capsule, indicating FSGS. Electron microscopy demonstrated abnormal aggregated mitochondria in podocytes, and the basement membrane and epithelial cells of Bowman's capsule. Skeletal muscle biopsy also showed accumulation of abnormal mitochondria. mtDNA analysis identified heteroplasmic mtDNA 3243A>G mutation with no large-scale deletions. From these findings, we diagnosed the case as CPEO with multi-organ involvement including FSGS. Our report demonstrates that CPEO, as well as MELAS, can be associated with FSGS. Because mitochondrial disease presents with a variety of clinical symptoms, atypical cases with non-classical manifestations are observed. Thus, mitochondrial disease should be considered as an underlying cause of FSGS with systemic manifestations even with atypical phenotypes.

Haematological abnormalities in mitochondrial disorders

INTRODUCTION

This study aimed to assess the kind of haematological abnormalities that are present in patients with mitochondrial disorders (MIDs) and the frequency of their occurrence.

METHODS

The blood cell counts of a cohort of patients with syndromic and non-syndromic MIDs were retrospectively reviewed. MIDs were classified as 'definite', 'probable' or 'possible' according to clinical presentation, instrumental findings, immunohistological findings on muscle biopsy, biochemical abnormalities of the respiratory chain and/or the results of genetic studies. Patients who had medical conditions other than MID that account for the haematological abnormalities were excluded.

RESULTS

A total of 46 patients ('definite' = 5; 'probable' = 9; 'possible' = 32) had haematological abnormalities attributable to MIDs. The most frequent haematological abnormality in patients with MIDs was anaemia. 27 patients had anaemia as their sole haematological problem. Anaemia was associated with thrombopenia (n = 4), thrombocytosis (n = 2), leucopenia (n = 2), and eosinophilia (n = 1). Anaemia was hypochromic and normocytic in 27 patients, hypochromic and microcytic in six patients, hyperchromic and macrocytic in two patients, and normochromic and microcytic in one patient. Among the 46 patients with a mitochondrial haematological abnormality, 78.3% had anaemia, 13.0% had thrombopenia, 8.7% had leucopenia and 8.7% had eosinophilia, alone or in combination with other haematological abnormalities.

CONCLUSION

MID should be considered if a patient's abnormal blood cell counts (particularly those associated with anaemia, thrombopenia, leucopenia or eosinophilia) cannot be explained by established causes. Abnormal blood cell counts may be the sole manifestation of MID or a collateral feature of a multisystem problem.

Novel 5.712 kb mitochondrial DNA deletion in a patient with Pearson syndrome: a case report

Pearson marrow‑pancreas syndrome (PS) is a progressive multi‑organ disorder caused by deletions and duplications of mitochondrial DNA (mtDNA). PS is often fatal in infancy, and the majority of patients with PS succumb to the disease before reaching three‑years‑of‑age, due to septicemia, metabolic acidosis or hepatocellular insufficiency. The present report describes the case of a four‑month‑old infant with severe normocytic normochromic anemia, vacuolization of hematopoietic precursors and metabolic acidosis. After extensive clinical investigation, the patient was diagnosed with PS, which was confirmed by molecular analysis of mtDNA. The molecular analysis detected a novel large‑scale (5.712 kb) deletion spanning nucleotides 8,011 to 13,722 of mtDNA, which lacked direct repeats at the deletion boundaries. The present report is, to the best of our knowledge, the first case reported in South Korea.

Inherited cobalamin malabsorption. Mutations in three genes reveal functional and ethnic patterns

BACKGROUND

Inherited malabsorption of cobalamin (Cbl) causes hematological and neurological abnormalities that can be fatal. Three genes have been implicated in Cbl malabsorption; yet, only about 10% of ~400-500 reported cases have been molecularly studied to date. Recessive mutations in CUBN or AMN cause Imerslund-Gräsbeck Syndrome (IGS), while recessive mutations in GIF cause Intrinsic Factor Deficiency (IFD). IGS and IFD differ in that IGS usually presents with proteinuria, which is not observed in IFD. The genetic heterogeneity and numerous differential diagnoses make clinical assessment difficult.

METHODS

We present a large genetic screening study of 154 families or patients with suspected hereditary Cbl malabsorption. Patients and their families have been accrued over a period spanning >12  years. Systematic genetic testing of the three genes CUBN, AMN, and GIF was accomplished using a combination of single strand conformation polymorphism and DNA and RNA sequencing. In addition, six genes that were contenders for a role in inherited Cbl malabsorption were studied in a subset of these patients.

RESULTS

Our results revealed population-specific mutations, mutational hotspots, and functionally distinct regions in the three causal genes. We identified mutations in 126/154 unrelated cases (82%). Fifty-three of 126 cases (42%) were mutated in CUBN, 45/126 (36%) were mutated in AMN, and 28/126 (22%) had mutations in GIF. We found 26 undescribed mutations in CUBN, 19 in AMN, and 7 in GIF for a total of 52 novel defects described herein. We excluded six other candidate genes as culprits and concluded that additional genes might be involved.

CONCLUSIONS

Cbl malabsorption is found worldwide and genetically complex. However, our results indicate that population-specific founder mutations are quite common. Consequently, targeted genetic testing has become feasible if ethnic ancestry is considered. These results will facilitate clinical and molecular genetic testing of Cbl malabsorption. Early diagnosis improves the lifelong care required by these patients and prevents potential neurological long-term complications. This study provides the first comprehensive overview of the genetics that underlies the inherited Cbl malabsorption phenotype.