Alpers-Huttenlocher Syndrome

Etiology

Alpers-Huttenlocher syndrome is a mitochondrial disorder caused by an autosomal recessive mutation in the POLG1 gene resulting in damage to polymerase gamma.[2] The inheritance of a heterozygous mutation in POLG1 leads to the classic presentation of the disease between 2 and 4 years of age.  However, the presence of a homozygous mutation in POLG1 is associated with a later and milder presentation, between 17 to 24 years of age.[3]

Epidemiology

Approximately 1 in 100000 children will develop Alpers-Huttenlocher syndrome, with males and females being affected equally. There appears to be a slightly higher carrier frequency in people of Northern European descent, although there are reports of the condition in many ethnic groups.[3]

Pathophysiology

An autosomal recessive mutation in POLG1 leads to decreased polymerase gamma functionality, leading to a reduction of mitochondrial DNA.[4] Mitochondria are present in high numbers in tissue with high energy requirements - such as the central nervous system, liver, and skeletal muscle. This reduction in mitochondrial support leads to the symptoms of AHS.[3]

Histopathology

The primary organs in Alpers-Huttenlocher syndrome demonstrating histologic changes are the liver and brain. Neural tissue from the cerebral cortex shows spongiosis, neuronal loss, and astrocytosis. These findings correlate with the progressive cognitive decline seen with the progression of the disease. The hepatic findings are more specific to AHS. A minimum of three of the following eight criteria must be present, in the absence of Wilson disease: bridging fibrosis or cirrhosis, bile ductular proliferation, the collapse of liver plate cells, hepatocyte dropout or focal necrosis with or without portal inflammation, microvesicular steatosis, oncocytic change, regenerative nodules, and parenchymal disease or disorganization of the normal lobular architecture.[5]

History and Physical

The first step to diagnosing Alpers-Huttenlocher syndrome is recognizing the triad of refractory seizures, psychomotor regression, and hepatopathy. Patients may experience blindness - first temporarily, but often permanently.  Other symptoms include migraines with possible hallucinations, ataxia, spastic paraparesis, cognitive impairment, anxiety, and depression.[6] A confirmation of the diagnosis is possible with polymerase gamma gene sequencing, liver biopsy, and ultimately autopsy.

Evaluation

Seizure activity is often an early feature of the disease and should undergo an evaluation with an electroencephalography (EEG). EEG findings in the early stages of the disease have shown a focal slowing of the frequency with epileptiform discharges from the occipital region.[3] One report showed that a characteristic EEG finding is unilateral occipital rhythmic high-amplitude delta with superimposed (poly)spikes (RHADS).[7] Brain magnetic resonance imaging (MRI) may aid in supporting an overall diagnosis of Alpers-Huttenlocher syndrome by showing gray matter involvement in the posterior cortical structures and thalamus, in addition to the involvement of the occipital cortex - the portion of the brain with the highest metabolic activity.[8]

Treatment / Management

Treatment for Alpers-Huttenlocher syndrome is supportive and eventually palliative. Clinicians should weigh the benefits of seizure management against the risk of side effects.  If prescribing anticonvulsants, the newer generation (lamotrigine, topiramate, oxcarbazepine, primidone) is the recommendation due to a lower hepatic processing burden. Valproic acid and sodium divalproate should be avoided to prevent accelerated hepatic damage. Impaired gluconeogenesis may lead to nutritional deficiencies.  Small, frequent, low-protein meals are recommended. Eventually, as the patient's disease progresses, a gastrostomy feeding tube can be offered to supplement nutritional status. Long-term respiratory support is often needed, with the use of tracheostomy and mechanical ventilation. Pain medications and muscle relaxants should be available to keep the patient comfortable.[3]

Differential Diagnosis

Alpers-Huttenlocher syndrome requires differentiation from the other mitochondrial disorders associated with POLG gene mutations. These include:

• Childhood myocerbro-hepatopathy
  • This disease has some overlapping features with AHS, so it is important to recognize the unique features. Childhood myocerebro-hepatopathy syndrome leads to liver failure and encephalopathy. Helpful distinguishing symptoms for this entity include lactic acidosis, hearing loss, cyclic vomiting, and lack of prominent seizure activity. This disease usually presents by six months of age - earlier than the typical onset of AHS, which is between 2 to 4 years old.[9] 
• Ataxia-neuropathy syndrome
• Myoclonus epilepsy myopathy sensory ataxia
• Autosomal recessive progressive external ophthalmoplegia plus
• Autosomal dominant progressive ophthalmoplegia plus.[10]

Toxicity and Adverse Effect Management

Valproic acid is appropriate in the management of seizures - a common feature in Alpers-Huttenlocher syndrome. However, valproic acid has been shown to cause a rapid progression of liver failure in patients with AHS. For this reason, it is critical to diagnose AHS early to avoid this medication and the detrimental effects it may have on the patient's clinical course.[3]

Prognosis

The prognosis for patients with Alpers-Huttenlocher syndrome is poor, with patients surviving less than 4 years after the initial presentation of symptoms. Common causes of death are fatal encephalopathy and liver failure.[1]

Complications

Patients with Alpers-Huttenlocher syndrome can expect to experience numerous complications with the progression of the disease. Several features of end-stage AHS may find their explanation with the specific neural structures affected. Blindness is attributable to damage to the occipital cortex. Ataxia is traceable to the loss of Purkinje cells in the cerebellum. Loss of central respiratory drive often leads to hypoxia and possibly placement of a tracheostomy tube. Spastic paraparesis results from damage to the cerebral cortex.  This spasticity may lead to difficulty walking, with the ultimate loss of the ability to walk. Decreased bulbar reflexes, in addition to muscle weakness, may cause dysphagia- leading patients to aspirate or become malnourished. If the dysphagia is severe, families may consider the placement of a gastrostomy tube.[6]