Hypothalamic growth hormone deficiency and supplementary GH therapy in two patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes

Red Flags in Primary Mitochondrial Diseases: What Should We Recognize?

Primary mitochondrial diseases (PMDs) are complex group of metabolic disorders caused by genetically determined impairment of the mitochondrial oxidative phosphorylation (OXPHOS). The unique features of mitochondrial genetics and the pivotal role of mitochondria in cell biology explain the phenotypical heterogeneity of primary mitochondrial diseases and the resulting diagnostic challenges that follow. Some peculiar features ("red flags") may indicate a primary mitochondrial disease, helping the physician to orient in this diagnostic maze. In this narrative review, we aimed to outline the features of the most common mitochondrial red flags offering a general overview on the topic that could help physicians to untangle mitochondrial medicine complexity.

Endocrine Manifestations and New Developments in Mitochondrial Disease

Mitochondrial diseases are a group of common inherited diseases causing disruption of oxidative phosphorylation. Some patients with mitochondrial disease have endocrine manifestations, with diabetes mellitus being predominant but also include hypogonadism, hypoadrenalism, and hypoparathyroidism. There have been major developments in mitochondrial disease over the past decade that have major implications for all patients. The collection of large cohorts of patients has better defined the phenotype of mitochondrial diseases and the majority of patients with endocrine abnormalities have involvement of several other systems. This means that patients with mitochondrial disease and endocrine manifestations need specialist follow-up because some of the other manifestations, such as stroke-like episodes and cardiomyopathy, are potentially life threatening. Also, the development and follow-up of large cohorts of patients means that there are clinical guidelines for the management of patients with mitochondrial disease. There is also considerable research activity to identify novel therapies for the treatment of mitochondrial disease. The revolution in genetics, with the introduction of next-generation sequencing, has made genetic testing more available and establishing a precise genetic diagnosis is important because it will affect the risk for involvement for different organ systems. Establishing a genetic diagnosis is also crucial because important reproductive options have been developed that will prevent the transmission of mitochondrial disease because of mitochondrial DNA variants to the next generation.

Overview of Atypical Diabetes

Although type 1 diabetes mellitus and, to a lesser extent, type 2 diabetes mellitus, are the prevailing forms of diabetes in youth, atypical forms of diabetes are not uncommon and may require etiology-specific therapies. By some estimates, up to 6.5% of children with diabetes have monogenic forms. Mitochondrial diabetes and cystic fibrosis related diabetes are less common but often noted in the underlying disease. Atypical diabetes should be considered in patients with a known disorder associated with diabetes, aged less than 25 years with nonautoimmune diabetes and without typical characteristics of type 2 diabetes mellitus, and/or with comorbidities associated with atypical diabetes.

Appendicular skeletal muscle mass: A more sensitive biomarker of disease severity than BMI in adults with mitochondrial diseases

The study aimed to evaluate the body composition of patients with mitochondrial diseases (MD) and correlate it with disease severity. Overall, 89 patients (age ≥ 18 years) with MD were recruited, including 49 with chronic progressive external ophthalmoplegia (CPEO) and 40 with mitochondrial encephalomyopathy with lactate acidosis and stroke-like episodes (MELAS). Body composition, including fat mass index (FMI), fat-free mass index (FFMI), skeletal muscle mass index (SMI), and appendicular skeletal muscle mass index (ASMI), were examined using multifrequency bioelectric impedance analysis. Clinical assessments, including muscle strength, usual gait speed, and disease severity determined by the Newcastle Mitochondrial Disease Adult Scale score (NMDAS), were performed. The comparisons between patients group and age- and gender-matched healthy controls, as well as the correlations between anthropometric measurements, body composition, and disease severity were analyzed. Height, weight, body mass index (BMI), FFMI, SMI, and ASMI were significantly lower in patients with MD than in healthy controls. Notably, low muscle mass was noted in 69.7% (62/89) of MD patients, with 22 patients also presenting with compromised physical performance as indicated by decreased gait speed, resulting in 24.7% satisfied the sarcopenia diagnostic criteria. Disease severity was more negatively correlated with ASMI than it was with height, weight, and BMI. Subgroup analysis showed that in the MELAS subgroup, disease severity was negatively correlated with height, weight, and ASMI; whereas in the CPEO subgroup, it was only negatively correlated with ASMI and SMI. Additionally, ASMI was positively associated with muscle strength. Altogether, compared with BMI, ASMI is a more sensitive biomarker predicting disease severity of MD, both in MELAS and CPEO patients.

Height as a Clinical Biomarker of Disease Burden in Adult Mitochondrial Disease

CONTEXT

Abnormal growth and short stature are observed in patients with mitochondrial disease, but it is unclear whether there is a relationship between final adult height and disease severity.

OBJECTIVE

To determine whether patients with genetically confirmed mitochondrial disease are shorter than their peers and whether stature is related to disease severity.

DESIGN

Analysis of final adult height in relation to disease severity as determined by the Newcastle Mitochondrial Disease Adult Scale (NMDAS).

SETTING

UK Mitochondrial Disease Patient Cohort (Mito Cohort).

PATIENTS

575 patients were identified with recorded height, weight, and molecular genetic diagnosis of mitochondrial disease within the Mito Cohort.

MAIN OUTCOME MEASURES

Adult height, body mass index (BMI), and their association with genetic subgroup and disease severity.

RESULTS

Adults with mitochondrial disease were short, with a mean height of -0.49 SD (95% CI, -0.58 to -0.39; n = 575) compared with UK reference data. Patients were overweight, with a BMI SD of 0.52 (95% CI, 0.37 to 0.67; n = 472). The most common genetic subgroup (m.3243A>G mutation) had a height SD of -0.70 (95% CI, -0.85 to -0.54; n = 234) and a BMI SD of 0.12 (95% CI, -0.10 to 0.34; n = 212). NMDAS scores were negatively correlated with height SD (r = -0.25; 95% CI, -0.33 to -0.17; P < 0.001, n = 533). Rate of disease progression also correlated negatively with adult height (P < 0.001).

CONCLUSION

Final height in mitochondrial disease reflects disease severity and rate of disease progression. Mitochondrial dysfunction and associated subclinical comorbidities affect growth plate physiology.

Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society

The purpose of this statement is to provide consensus-based recommendations for optimal management and care for patients with primary mitochondrial disease. This statement is intended for physicians who are engaged in the diagnosis and management of these patients. Working group members were appointed by the Mitochondrial Medicine Society. The panel included members with several different areas of expertise. The panel members utilized surveys and the Delphi method to reach consensus. We anticipate that this statement will need to be updated as the field continues to evolve. Consensus-based recommendations are provided for the routine care and management of patients with primary genetic mitochondrial disease.

Mitochondrial disease and endocrine dysfunction

Mitochondria are critical organelles for endocrine health; steroid hormone biosynthesis occurs in these organelles and they provide energy in the form of ATP for hormone production and trafficking. Mitochondrial diseases are multisystem disorders that feature defective oxidative phosphorylation, and are characterized by enormous clinical, biochemical and genetic heterogeneity. To date, mitochondrial diseases have been found to result from >250 monogenic defects encoded across two genomes: the nuclear genome and the ancient circular mitochondrial genome located within mitochondria themselves. Endocrine dysfunction is often observed in genetic mitochondrial diseases and reflects decreased intracellular production or extracellular secretion of hormones. Diabetes mellitus is the most frequently described endocrine disturbance in patients with inherited mitochondrial diseases, but other endocrine manifestations in these patients can include growth hormone deficiency, hypogonadism, adrenal dysfunction, hypoparathyroidism and thyroid disease. Although mitochondrial endocrine dysfunction frequently occurs in the context of multisystem disease, some mitochondrial disorders are characterized by isolated endocrine involvement. Furthermore, additional monogenic mitochondrial endocrine diseases are anticipated to be revealed by the application of genome-wide next-generation sequencing approaches in the future. Understanding the mitochondrial basis of endocrine disturbance is key to developing innovative therapies for patients with mitochondrial diseases.

Efficacy of growth hormone therapy in Kearns-Sayre syndrome: the KIGS experience

Kearns-Sayre syndrome (KSS) is characterized by external ophthalmoplegia, retinal pigmentation and cardiac conduction defects due to mitochondrial DNA (mtDNA) deletions. Short stature and growth hormone (GH) deficiency have been reported in KSS, but data on GH treatment is limited. We describe the clinical presentation, phenotype evolution, and response to GH in a patient with KSS and report data on eight additional KSS patients from the KIGS database. Our patient with KSS and GH deficiency achieved a final adult height at -0.8 SDS. In the KIGS database GH treatment resulted in mean improvement in height from -3.9 to -2.9 SDS in patients with KSS. Two patients did not show growth improvement. Our data shows improvement in height SDS in our patient and mixed results in eight additional patients from the KIGS database after treatment with GH. Heterogeneity in responsiveness may relate to presence of GH deficiency or severity of underlying mitochondrial dysfunction.

Maternally-inherited diabetes with deafness (MIDD) and hyporeninemic hypoaldosteronism

Maternally-inherited diabetes with deafness (MIDD) is a rare form of monogenic diabetes that results, in most cases, from an A-to-G transition at position 3243 of mitochondrial DNA (m.3243A>G) in the mitochondrial-encoded tRNA leucine (UUA/G) gene. As the name suggests, this condition is characterized by maternally-inherited diabetes and bilateral neurosensory hearing impairment. A characteristic of mitochondrial cytopathies is the progressive multisystemic involvement with the development of more symptoms during the course of the disease. We report here the case of a patient with MIDD who developed hyporeninemic hypoaldosteronism.

Endocrine disorders in mitochondrial disease

Endocrine dysfunction in mitochondrial disease is commonplace, but predominantly restricted to disease of the endocrine pancreas resulting in diabetes mellitus. Other endocrine manifestations occur, but are relatively rare by comparison. In mitochondrial disease, neuromuscular symptoms often dominate the clinical phenotype, but it is of paramount importance to appreciate the multi-system nature of the disease, of which endocrine dysfunction may be a part. The numerous phenotypes attributable to pathogenic mutations in both the mitochondrial (mtDNA) and nuclear DNA creates a complex and heterogeneous catalogue of disease which can be difficult to navigate for novices and experts alike. In this article we provide an overview of the endocrine disorders associated with mitochondrial disease, the way in which the underlying mitochondrial disorder influences the clinical presentation, and how these factors influence subsequent management.

Neuromuscular and systemic presentations in adults: diagnoses beyond MERRF and MELAS

Mitochondrial diseases are a diverse group of inherited and acquired disorders that result in inadequate energy production. They can be caused by inheritable genetic mutations, acquired somatic mutations, and exposure to toxins (including some prescription medications). Normal mitochondrial physiology is responsible, in part, for the aging process itself, as free radical production within the mitochondria results in a lifetime burden of oxidative damage to DNA, especially the mitochondrial DNA that, in turn, replicate the mutational burden in future copies of itself, and lipid membranes. Primary mitochondrial diseases are those caused by mutations in genes that encode for mitochondrial structural and enzymatic proteins, and those proteins required for mitochondrial assembly and maintenance. A number of common adult maladies are associated with defective mitochondrial energy production and function, including diabetes, obesity, hyperthyroidism, hypothyroidism, and hyperlipidemia. Mitochondrial dysfunction has been demonstrated in many neurodegenerative disorders, including Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and some cancers. Polymorphisms in mitochondrial DNA have been linked to disease susceptibility, including death from sepsis and survival after head injury. There is considerable overlap in symptoms caused by primary mitochondrial diseases and those illnesses that affect mitochondrial function, but are not caused by primary mutations, as well as disorders that mimic mitochondrial diseases, but are caused by other identified mutations. Evaluation of these disorders is complex, expensive, and not without false-negative and false-positive results that can mislead the physician. Most of the common heritable mitochondrial disorders have been well-described in the literature, but can be overlooked by many clinicians if they are uneducated about these disorders. In general, the evaluation of the classic mitochondrial disorders has become straightforward if the clinician recognized the phenotype and orders appropriate confirmatory testing. However, the majority of patients referred for a mitochondrial evaluation do not have a clear presentation that allows for rapid identification and testing. This article provides introductory comments on mitochondrial structure, physiology, and genetics, but will focus on the presentation and evaluation of adults with mitochondrial symptoms, but who may not have a primary mitochondrial disease.

Mitochondrial diseases in childhood: a clinical approach to investigation and management

Mitochondrial diseases are a common cause of inherited neurological disorders in children. Although dysfunction of the central nervous system is prominent, multisystem involvement also occurs. Diagnosis relies on characteristic clinical features, an understanding of mitochondrial genetics, and a logical, informed approach to investigations. There is a significant body of recent literature on advances in mitochondrial genetics and the investigation of mitochondrial diseases. However, to our knowledge there remains a paucity of published information on the management of these disorders. Management of the complex constellation of neurological and multisystem clinical features is challenging, and is reliant on a multidisciplinary approach. The care of the child and family is dependent on clear communication between health professionals from primary, secondary, and tertiary care as well as specialist input from quaternary services. The aim of this review is to provide paediatric neurologists, paediatricians, and allied health professionals with a structured approach to the diagnosis and management of children with suspected or confirmed mitochondrial disease.

Clinical features, diagnosis and management of maternally inherited diabetes and deafness (MIDD) associated with the 3243A>G mitochondrial point mutation

Maternally inherited diabetes and deafness (MIDD) affects up to 1% of patients with diabetes but is often unrecognized by physicians. It is important to make an accurate genetic diagnosis, as there are implications for clinical investigation, diagnosis, management and genetic counselling. This review summarizes the range of clinical phenotypes associated with MIDD; outlines the advances in genetic diagnosis and pathogenesis of MIDD; summarizes the published prevalence data and provides guidance on the clinical management of these patients and their families.

Variable outcome of growth hormone administration in respiratory chain deficiency

Genetic defects of oxidative phosphorylation (OXPHOS) are known to account for a variety of neuromuscular and non-neuromuscular symptoms in childhood, including growth hormone (GH) deficiency. However GH administration for GH deficiency is controversial in OXPHOS deficiencies as GH is a mitosis-stimulator which may increase energy demand for cell proliferation. Here, we report the observation of four unrelated children with OXPHOS deficiency or bearing a mitochondrial DNA rearrangement and growth retardation, who required GH therapy. The first patient had no GH deficiency while the other three had low GH response to test stimulations. The condition of the first two patients quickly deteriorated under GH administration, GH was then stopped and subsequent clinical improvement was noted. In the other two patients, no adverse event was noted but various additional organs were involved following GH administration. In all patients, no benefit was observed concerning growth response as growth speed remained unchanged. These observations question the use of GH as a treatment of growth retardation for patients with OXPHOS deficiency.

Mitochondrial DNA deletion in a child with mitochondrial encephalomyopathy, growth hormone deficiency, and hypoparathyroidism

We report an 11-year-old boy with short stature, bilateral ptosis, sensorineural hearing loss, muscle weakness, and endocrine abnormalities. Brain magnetic resonance imaging (MRI) showed a bilateral abnormal signal in the globus pallidus and in the midbrain tegment. Muscle biopsy specimens showed ragged red and cytochrome c oxidase negative fibers, and biochemical analysis of muscle homogenate showed a partial defect of complex I and IV activities of the respiratory chain enzymes. Analysis of mitochondrial DNA by a polymerase chain reaction screening procedure and Southern blot revealed a novel heteroplasmic single mitochondrial DNA deletion of 7.8 kb in different tissues. This deletion was absent in the blood DNA of his mother and brother. This case further expands and confirms the wide clinical spectrum of mitochondrial disorders associated with single large-scale mitochondrial DNA deletions.

Long-Term Growth Hormone Therapy in Mitochondrial Cytopathy

OBJECTIVE

To describe in a 5-year-old Caucasian male with mitochondrial cytopathy, a biochemical growth hormone (GH) deficiency associated with normal GH biological activity as evaluated by Nb2 cell bioassay and normal serum IGF-I and IGFBP3 values increasing slightly after GH administration.

METHOD

Serum GH concentrations were measured with a commercial immunofluorometric assay and with a biological assay, which uses the Nb2 cell line. Serum IGF-I and IGFBP3 concentrations were measured with RIA.

RESULTS

The GH-supplementary therapy was initially effective in terms of growth gain, but no therapeutic benefit was observed over a long period of time.

CONCLUSION

In patients suffering from mitochondrial cytopathy, short stature seems to be attributed more to a disease-related inadequate protein substrate than to the non-classical GH deficiency.