Acromutilating, paralyzing neuropathy with corneal ulceration in Navajo children

Genetic pain loss disorders

Genetic pain loss includes congenital insensitivity to pain (CIP), hereditary sensory neuropathies and, if autonomic nerves are involved, hereditary sensory and autonomic neuropathy (HSAN). This heterogeneous group of disorders highlights the essential role of nociception in protecting against tissue damage. Patients with genetic pain loss have recurrent injuries, burns and poorly healing wounds as disease hallmarks. CIP and HSAN are caused by pathogenic genetic variants in >20 genes that lead to developmental defects, neurodegeneration or altered neuronal excitability of peripheral damage-sensing neurons. These genetic variants lead to hyperactivity of sodium channels, disturbed haem metabolism, altered clathrin-mediated transport and impaired gene regulatory mechanisms affecting epigenetic marks, long non-coding RNAs and repetitive elements. Therapies for pain loss disorders are mainly symptomatic but the first targeted therapies are being tested. Conversely, chronic pain remains one of the greatest unresolved medical challenges, and the genes and mechanisms associated with pain loss offer new targets for analgesics. Given the progress that has been made, the coming years are promising both in terms of targeted treatments for pain loss disorders and the development of innovative pain medicines based on knowledge of these genetic diseases.

Mitochondrial DNA Depletion Syndromes

Mitochondrial disorders present in a myriad of ways, which causes them to be included in the differential diagnosis for many patients with undiagnosed disease. A subset of mitochondrial disorders are caused by intrinsic defects in the mitochondrial replication machinery, leading to loss of cellular mitochondrial content over time. The diagnosis of mitochondrial disease is complex. Several best-practice guides are available that enable a higher likelihood of detecting a mitochondrial disorder. The application of genomic sequencing and advanced physiologic analysis of the electron transport chain can offer more definitive evidence of mitochondrial dysfunction.

Neuromuscular Manifestations in Mitochondrial Diseases in Children

Mitochondrial diseases exhibit significant clinical and genetic heterogeneity. Mitochondria are highly dynamic organelles that are the major contributor of adenosine triphosphate, through oxidative phosphorylation. These disorders may be developed at any age, with isolated or multiple system involvement, and in any pattern of inheritance. Defects in the mitochondrial respiratory chain impair energy production and almost invariably involve skeletal muscle and peripheral nerves, causing exercise intolerance, cramps, recurrent myoglobinuria, or fixed weakness, which often affects extraocular muscles and results in droopy eyelids (ptosis), progressive external ophthalmoplegia, peripheral ataxia, and peripheral polyneuropathy. This review describes the main neuromuscular symptomatology through different syndromes reported in the literature and from our experience. We want to highlight the importance of searching for the "clue clinical signs" associated with inheritance pattern as key elements to guide the complex diagnosis process and genetic studies in mitochondrial diseases.

MPV17-related hepatocerebral mitochondrial DNA depletion syndrome (MPV17-NNH) revisited

MPV17-related hepatocerebral mitochondrial DNA depletion syndrome (previously known as Navajo neurohepatopathy) was discovered in children in the Four Corner's region of New Mexico approximately 40 years ago. This disease is associated with a single missense mutation in exon 2 in the MPV17 gene. The syndrome has now been recognized world-wide. We find that huge quantities of neurotoxins were present in archived nervous tissues from such patients. Arsenic was increased 18 ×, cadmium ~ 10 ×, cobalt 2.5 × and manganese 2.3 ×; the largest increase was in mercury content 16,000 × compared to contemporaneous fresh-frozen normal nervous tissues. In the Four Corner's region of NM the life span is reduced compared to other parts of the United States and in our patients with MPV17-NNH the average life span was 5.4 years ± 2.7 (SE) years. We now live in the Anthropocene an epoch characterized by large additions to the biosphere of neurotoxins. The effects of such toxic loads on human health and disease remain to be assessed. We speculate how such high neurotoxin content in tissues, which is likely to increase during the Anthropocene, may have influenced MPV17-NNH and similar phenotypes in different parts of the world. Our results imply that selenium supplementation to the diet in the Four Corner's region of NM might be beneficial to normal people and in the management of patients with MPV17-NNH syndrome.

Environmental exposures to metals in Native communities and implications for child development: basis for the Navajo birth cohort study

Two disparate statistics often cited for the Western United States raise concern about risks for developmental disabilities in Native American children. First, 13 of the states with the highest percentage of Native American population are located in the Western United States (U.S. Census Bureau, 2012 ). Second, more than 161,000 abandoned hard-rock mines are located in 12 Western states (General Accounting Office, 2014 ). Moreover, numerous studies have linked low-level metals exposure with birth defects and developmental delays. Concern has emerged among tribal populations that metals exposure from abandoned mines might threaten development of future generations.

A novel MPV17 gene mutation in a Saudi infant causing fatal progressive liver failure

We describe in this report the clinical, biochemical, and molecular features of a Saudi infant with hepatocerebral MDS secondary to a novel homozygous mutation in the MPV17 gene. An automated sequencing of the nuclear MPV17 gene was performed. The coding region (7 exons) of the MPV17 gene was amplified using an M13-tagged intronic primer and screened by direct sequencing of the PCR-amplified products (GenBank Association Number NM_002437.4). The sequencing of the entire coding region and intron-exon boundaries of MPV17 gene revealed a single homozygous variant, -c.278A > C(p.Q93P), which predicts the substitution of a highly conserved amino acid. This particular sequence variant has not been previously reported as a single-nucleotide polymorphism (SNP) or pathogenic mutation. Diagnostic workup for neonatal liver disorders should include mutation screening for known genes. The new advances in molecular genetics can help clinicians establish the diagnosis in a timely fashion, which may prevent a child from undergoing invasive and expensive investigations.

Peripheral neuropathy associated with mitochondrial disease in children

Mitochondrial diseases in children are often associated with a peripheral neuropathy but the presence of the neuropathy is under-recognized because of the overwhelming involvement of the central nervous system (CNS). These mitochondrial neuropathies are heterogeneous in their clinical, neurophysiological, and histopathological characteristics. In this article, we provide a comprehensive review of childhood mitochondrial neuropathy. Early recognition of neuropathy may help with the identification of the mitochondrial syndrome. While it is not definite that the characteristics of the neuropathy would help in directing genetic testing without the requirement for invasive skin, muscle or liver biopsies, there appears to be some evidence for this hypothesis in Leigh syndrome, in which nuclear SURF1 mutations cause a demyelinating neuropathy and mitochondrial DNA MTATP6 mutations cause an axonal neuropathy. POLG1 mutations, especially when associated with late-onset phenotypes, appear to cause a predominantly sensory neuropathy with prominent ataxia. The identification of the peripheral neuropathy also helps to target genetic testing in the mitochondrial optic neuropathies. Although often subclinical, the peripheral neuropathy may occasionally be symptomatic and cause significant disability. Where it is symptomatic, recognition of the neuropathy will help the early institution of rehabilitative therapy. We therefore suggest that nerve conduction studies should be a part of the early evaluation of children with suspected mitochondrial disease.

Hand involvement in Navajo neurohepatopathy: a case report

We report a case of Navajo neurohepatopathy with severe involvement of the hands. It is a progressive sensorimotor neuropathy with distal weakness, areflexia, and reduced sensation in the extremities associated with acral mutilation. The role of possible surgical intervention is demonstrated in this case.

Inherited mitochondrial neuropathies

Mitochondrial disorders (MIDs) occasionally manifest as polyneuropathy either as the dominant feature or as one of many other manifestations (inherited mitochondrial neuropathy). MIDs in which polyneuropathy is the dominant feature, include NARP syndrome due to the transition m.8993T>, CMT2A due to MFN2 mutations, CMT2K and CMT4A due to GDAP1 mutations, and axonal/demyelinating neuropathy with external ophthalmoplegia due to POLG1 mutations. MIDs in which polyneuropathy is an inconstant feature among others is the MELAS syndrome, MERRF syndrome, LHON, Mendelian PEO, KSS, Leigh syndrome, MNGIE, SANDO; MIRAS, MEMSA, AHS, MDS (hepato-cerebral form), IOSCA, and ADOA syndrome. In the majority of the cases polyneuropathy presents in a multiplex neuropathy distribution. Nerve conduction studies may reveal either axonal or demyelinated or mixed types of neuropathies. If a hereditary neuropathy is due to mitochondrial dysfunction, the management of these patients is at variance from non-mitochondrial hereditary neuropathies. Patients with mitochondrial hereditary neuropathy need to be carefully investigated for clinical or subclinical involvement of other organs or systems. Supportive treatment with co-factors, antioxidants, alternative energy sources, or lactate lowering agents can be tried. Involvement of other organs may require specific treatment. Mitochondrial neuropathies should be included in the differential diagnosis of hereditary neuropathies.

Orthopaedic manifestations of Navajo familial neurogenic arthropathy

BACKGROUND

Navajo Familial Neurogenic Arthropathy is a disease identified in Navajo children, primarily residing in Arizona, New Mexico, and Utah. To date, there are no reports in the orthopaedic literature regarding this disorder, particularly the clinical manifestations and treatment considerations.

METHODS

We carried out a retrospective chart and radiographic review of 2 patients with Navajo familial neurogenic arthropathy. We present these 2 patients as representative of the orthopaedic manifestations of Navajo familial neurogenic arthropathy.

RESULTS

Both patients have significant axial and appendicular bone abnormalities, Charcot-type arthopathy, heat intolerance and also anhidrosis. They have normal intelligence. Both patients underwent surgical interventions, with recurrent deformity and infection being the most common complications.

CONCLUSIONS

Navajo familial neurogenic arthropathy is a rare clinical entity, seen most commonly in the southwestern regions of the United States. Patients are found to have a myriad of orthopaedic abnormalities, and surgical intervention, while sometimes indicated, can be fraught with complications.

LEVEL OF EVIDENCE

Level IV, case series.

Autosomal recessive diseases among the Athabaskans of the southwestern United States: recent advances and implications for the future

Genetic and linguistic data suggest that the Na-Dene, of which the Athabaskans are the largest group, are part of a later immigration into the Americas than the first Amerind immigration. Whether a second and third immigration can be separated seems unlikely but continued cross-Bering Strait exchanges may have masked what was a greater separation in the past. The movement of tribes into Siberia appears to have involved a genetic bottleneck leading to at least one disease allele shared by Eskimo/Aleuts and Navajos and a second possibly shared by the Navajo and a Siberian population, but not the same Siberian population that share deep linguistic affinities with the Navajo. A second bottleneck appears to have occurred with the migration of Athabaskans from Northwest North America to the Southwestern United States along the Rocky Mountains. This bottleneck is reflected in several rare recessive diseases shared by the Navajo and Apache. Finally, the Navajo were captured and imprisoned under conditions which led to severe population loss. This, and the "hiding away" of a small number of Navajos in what is now the Western portion of the reservation, led to a Navajo-specific bottleneck(s) resulting in an increased frequency of several rare recessive diseases among the Navajo. Prejudice against human genetic research is high among the Southwestern Athabaskans but attempts to bridge the gap are now occurring. The involvement of Navajo scientists in this process is especially encouraging.

Early-onset liver mtDNA depletion and late-onset proteinuric nephropathy in Mpv17 knockout mice

In humans, MPV17 mutations are responsible for severe mitochondrial depletion syndrome, mainly affecting the liver and the nervous system. To gain insight into physiopathology of MPV17-related disease, we investigated an available Mpv17 knockout animal model. We found severe mtDNA depletion in liver and, albeit to a lesser extent, in skeletal muscle, whereas hardly any depletion was detected in brain and kidney, up to 1 year after birth. Mouse embryonic fibroblasts did show mtDNA depletion, but only after several culturing passages, or in a serumless culturing medium. In spite of severe mtDNA depletion, only moderate decrease in respiratory chain enzymatic activities, and mild cytoarchitectural alterations, were observed in the Mpv17^−/− livers, but neither cirrhosis nor failure ever occurred in this organ at any age. The mtDNA transcription rate was markedly increased in liver, which could contribute to compensate the severe mtDNA depletion. This phenomenon was associated with specific downregulation of Mterf1, a negative modulator of mtDNA transcription. The most relevant clinical features involved skin, inner ear and kidney. The coat of the Mpv17^−/− mice turned gray early in adulthood, and 18-month or older mice developed focal segmental glomerulosclerosis (FSGS) with massive proteinuria. Concomitant degeneration of cochlear sensory epithelia was reported as well. These symptoms were associated with significantly shorter lifespan. Coincidental with the onset of FSGS, there was hardly any mtDNA left in the glomerular tufts. These results demonstrate that Mpv17 controls mtDNA copy number by a highly tissue- and possibly cytotype-specific mechanism.

Lack of founder effect for an identical mtDNA depletion syndrome (MDS)-associated MPV17 mutation shared by Navajos and Italians

Navajo neurohepatopathy is a hepato-cerebral variant of mitochondrial DNA depletion syndrome due to a specific mutation in MPV17, a gene located on human chromosome 2p. The same mutation was reported in an Italian family. To understand whether the MPV17 mutation was transmitted by descent from a common ancestor to Navajos and Italians we constructed a dense haplotype of the MPV17 locus using suitable single nucleotide polymorphisms. Complete discordance between Italian and Navajo haplotypes rules out the former hypothesis, suggesting that the mutation occurred independently in the two populations.

Autonomic Peripheral Neuropathy

Most generalized peripheral polyneuropathies are accompanied by clinical or subclinical autonomic dysfunction. There is a group of peripheral neuropathies in which the small or unmyelinated fibers are selectively targeted. In these neuropathies, autonomic dysfunction is the most prominent manifestation. The features associated with an autonomic neuropathy include impairment of cardiovascular, gastrointestinal, urogenital, thermoregulatory, sudomotor, and pupillomotor autonomic function.

Congenital Corneal Anesthesia

Congenital corneal anesthesia is a rare clinical entity that poses a diagnostic dilemma, particularly in the pediatric age group. The sensory deficit may be confined to the cornea, or extend to other divisions of the trigeminal nerve. The sensory deficit may occur as an isolated abnormality, as part of a complex neurological syndrome, or it may occur in association with multiple somatic abnormalities and congenital insensitivity to pain. This condition usually presents between the ages of 8 to 12 months. Poor vision, photophobia, conjunctival injection, and corneal ulceration in the absence of pain and distress in a child should alert the clinician to the possibility of anesthetic cornea. In the early stages of presentation, punctuate keratopathy is the main feature, which may progress to non-healing persistent corneal epithelial defects. This stage may progress to acute corneal lysis and perforation. In most patients, conservative approaches such as copious lubrication, prevention of self-harm and cautious use of bandage contact lenses are effective in preventing progressive corneal damage. Tarsorrhapy is effective in promoting epithelial healing and permanent lateral tarsorraphy may prevent further development of epithelial defects. Amniotic membrane graft may be considered in order to improve epithelial healing. Corneal grafts carry a poor prognosis. Accurate initial diagnosis, evaluation, and proper management are paramount to prevent visual loss due to long-term complications of corneal anesthesia. This review of the literature outlines the problems and approaches in diagnosis, evaluation, and management of this rare condition.

Navajo neurohepatopathy is caused by a mutation in the MPV17 gene

Navajo neurohepatopathy (NNH) is an autosomal recessive disease that is prevalent among Navajo children in the southwestern United States. The major clinical features are hepatopathy, peripheral neuropathy, corneal anesthesia and scarring, acral mutilation, cerebral leukoencephalopathy, failure to thrive, and recurrent metabolic acidosis with intercurrent infections. Infantile, childhood, and classic forms of NNH have been described. Mitochondrial DNA (mtDNA) depletion was detected in the livers of two patients, suggesting a primary defect in mtDNA maintenance. Homozygosity mapping of two families with NNH suggested linkage to chromosome 2p24. This locus includes the MPV17 gene, which, when mutated, causes a hepatocerebral form of mtDNA depletion. Sequencing of the MPV17 gene in six patients with NNH from five families revealed the homozygous R50Q mutation described elsewhere. Identification of a single missense mutation in patients with NNH confirms that the disease is probably due to a founder effect and extends the phenotypic spectrum associated with MPV17 mutations.

Autonomic peripheral neuropathy

The autonomic neuropathies are a group of disorders in which the small, lightly myelinated and unmyelinated autonomic nerve fibres are selectively targeted. Autonomic features, which involve the cardiovascular, gastrointestinal, urogenital, sudomotor, and pupillomotor systems, occur in varying combination in these disorders. Diabetes is the most common cause of autonomic neuropathy in more developed countries. Autonomic neuropathies can also occur as a result of amyloid deposition, after acute infection, as part of a paraneoplastic syndrome, and after exposure to neurotoxins including therapeutic drugs. Certain antibodies (eg, anti-Hu and those directed against neuronal nicotinic acetylcholine receptor) are associated with autonomic signs and symptoms. There are several familial autonomic neuropathies with autosomal dominant, autosomal recessive, or X-linked patterns of inheritance. Autonomic dysfunction can occur in association with specific infections. The availability of sensitive and reproducible measures of autonomic function has improved physicians' ability to diagnose these disorders.

Gastrointestinal manifestations of mitochondrial disease

Although non-specific gastrointestinal and hepatic symptoms are commonly found in most mitochondrial disorders, they are among the cardinal manifestations of several primary mitochondrial diseases, such as: mitochondrial neurogastrointestinal encephalomyopathy; mitochondrial DNA depletion syndrome; Alpers syndrome; and Pearson syndrome. Management of these heterogeneous disorders includes the empiric supplementation with various "mitochondrial cocktails," supportive therapies, and avoidance of drugs and conditions known to have a detrimental effect on the respiratory chain. There is a great need for improved methods of treatment and controlled clinical trials of existing therapies. Liver transplantation is successful in acquired cases; however neuromuscular involvement in primary mitochondrial disorders should be a contraindication for liver transplantation.

Metachromatic leukodystrophy in the Navajo: fallout of the American-Indian wars of the nineteenth century

Our aim was to determine if the high frequency of metachromatic leukodystrophy (MLD) in Navajo Indians of the Southwestern United States is the result of a "genetic bottleneck" that occurred in the mid 19th century. Navajo Nation, Indian Health Service, and other national databases were queried for Native American patients with MLD. Pedigrees, including birth location, were established by interviewing relatives. We found that cases of MLD and their ancestors are clustered in a portion of the western Navajo Nation to which a small number of Navajo fled after armed conflict with the United States Army in the 1860s. The observed incidence of MLD on the western Navajo Nation is 1/2,520 live births, with an estimated carrier frequency of 1/25 to 1/50. No cases were observed in the eastern part of the Navajo Nation over a period of 18 years (60,000 births). The high incidence of MLD in the western Navajo Nation appears to be the result of a genetic bottleneck and probable founder effect from the mid 19th century: This mechanism may also explain the high incidence of a number of other unique, heritable disorders among the Navajo. The history of the Navajo may also be relevant to other American Indian and Alaskan Native groups that have undergone severe population reduction since the arrival of Europeans in North America.

Liver disease in Navajo neuropathy

OBJECTIVE

To describe clinical and histologic features of liver disease in infants and children with Navajo neuropathy (NN).

METHODS

Physicians at Navajo Area Indian Health Service facilities and neurologists and gastroenterologists at regional referral hospitals were surveyed for identification of patients born between 1980 and 1994 with known or suspected NN. Clinical records and liver histologic findings were reviewed.

RESULTS

Liver disease was present in all children with NN. Three clinical phenotypes of NN were observed, based on age at presentation and course: infantile NN presented in 5 infants before 6 months of age with jaundice and failure to thrive and progressed to liver failure before 2 years of age; childhood NN presented in 6 children between 1 and 5 years of age with liver dysfunction, which progressed to liver failure and death within 6 months; and classical NN presented in 9 children with variable onset of liver disease but progressive neurologic deterioration. Liver histologic findings were characterized by multinucleate giant cells, macrovesicular and microvesicular steatosis, pseudo-acini, inflammation, cholestasis, and bridging fibrosis and cirrhosis. Cases of all 3 phenotypes occurred within the same kindred.

CONCLUSIONS

Liver disease is an important component of NN and may be the predominant feature in infants and young children. We propose changing the name of this disease to Navajo neurohepatopathy.

Southwestern Athabaskan (Navajo and Apache) genetic diseases

PURPOSE

Four apparently unique disorders are known among the Southwestern Athabasan Amerindians, i.e., the Navajo and Apache; they are Athabaskan severe combined immunodeficiency, Navajo neuropathy, Navajo poikiloderma, and Athabaskan brainstem dysgenesis. This study reviews background information on Athabaskan groups and clinical descriptions of these recessive disorders.

METHODS

The major clinical findings of these four disorders are reviewed. In addition, the findings of epidemiological surveys are included where available.

RESULTS

Although the importance of genetic bottlenecks in increasing the frequency of rare, sometimes unique, autosomal recessive disorders is known for a number of populations, similar phenomena among Native Americans seem to be less well known.

CONCLUSION

As many more Native Americans move off the Reservation, the awareness of susceptibility to particular genetic diseases needs to be more widely disseminated.

Mitochondria and childhood liver diseases

The newly recognized mitochondrial hepatopathies should be considered in the differential diagnosis of acute and chronic liver disease in childhood. It may appear as neonatal liver failure, delayed onset liver failure in early childhood or as a multisystemic process. Comparison of features of several of the known primary mitochondrial hepatopathies is provided in Table 5. Secondary mitochondrial hepatopathies are examples of the critical importance of mitochondrial function in the pathogenesis of liver injury. Our improved understanding of the role of the mitochondria in cellular necrosis and apoptosis opens the way for development of new therapeutic approaches to several hepatic disorders. Primary mitochondrial hepatopathies (especially the respiratory chain defects) should be considered in any child with liver disease and neuromuscular involvement, multisystemic disease, lactic acidosis or rapidly progressive disease, and when hepatic steatosis is the dominant histologic finding on examination of a liver specimen. Current therapies are inadequate; improved therapeutic strategies are needed for these disorders. Some patients with respiratory chain defects limited to the liver have had successful liver transplantation. This field is in evolution and will undoubtedly provide new and important developments as the next millennium begins.

Spastic paraparesis and sensory neuropathy

A 12-year-old developed a slowly progressive spastic gait at the age of 3. A marked loss of pain and temperature sensations led to a mutilating acropathy starting at age 5. Electrodiagnostic studies revealed a symmetric, axonal, predominantly sensory neuropathy, and magnetic resonance imaging ruled out compression of spinal cord. Sural nerve biopsy disclosed a predominant involvement of unmyelinated and a global loss of myelinated fibers, particularly larger ones. Clinical, electrodiagnostic and pathological findings of this case most likely represent an example of the "Cavanagh's variant", an unusual but distinct entity within the hereditary sensory and autonomic neuropathies.

Familial congenital corneal anaesthesia

Congenital corneal anaesthesia is a cause of severe corneal ulceration and scarring in childhood. Although uncommon, it may be underdiagnosed when present as an isolated entity. Measures such as the use of elbow splints and tarsorrhaphy may be necessary to prevent visual loss. In rare instances, the condition may be inherited. A family is presented with autosomal dominant isolated congenital corneal anaesthesia, and the systemic associations and treatment of the condition are reviewed.

[Quantitative and electron microscope study of the nerve in seven cases of sporadic idiopathic sensory neuropathy (author's transl)]

An electron microscope study and quantitation of myelinated and unmyelinated fibers of seven nerve biopsies performed in sporadic cases of idiopathic sensory neuropathy is reported. The number of myelinated fibers is markedly decreased or absent in every case. On the contrary, the unmyelinated fiber numbers are normal or increased. In most cases, the small diameter myelinated and unmyelinated fibers proportions are higher than those of control biopsies. The electron microscope study discloses evidence of degeneration of Wallerian tye and regeneration is also indicated by quantitative studies. Regenerative phenomena seen more obvious in sporadic cases than in previously reported studies of familial cases.