Tag Archives: Hypotonia

Leigh Syndrome

What is Leigh syndrome?
Leigh syndrome is a severe neurological disorder that typically arises in the first year of life. This condition is characterized by progressive loss of mental and movement abilities (psychomotor regression) and typically results in death within a couple of years, usually due to respiratory failure. A small number of individuals develop symptoms in adulthood or have symptoms that worsen more slowly.

The first signs of Leigh syndrome seen in infancy are usually vomiting, diarrhea, and difficulty swallowing (dysphagia) that leads to eating problems. These problems often result in an inability to grow and gain weight at the expected rate (failure to thrive). Severe muscle and movement problems are common in Leigh syndrome. Affected individuals may develop weak muscle tone (hypotonia), involuntary muscle contractions (dystonia), and problems with movement and balance (ataxia). Loss of sensation and weakness in the limbs (peripheral neuropathy), common in people with Leigh syndrome, may also make movement difficult.

Several other symptoms may occur in people with Leigh syndrome. Many affected individuals develop weakness or paralysis of the muscles that move the eyes (ophthalmoparesis); rapid, involuntary eye movements (nystagmus); or degeneration of the nerves that carry information from the eyes to the brain (optic atrophy). Severe breathing problems are common in people with Leigh syndrome, and these problems can worsen until they cause acute respiratory failure. Some affected individuals develop hypertrophic cardiomyopathy, which is a thickening of the heart muscle that forces the heart to work harder to pump blood. In addition, a substance called lactate can build up in the body, and excessive amounts are often found in the blood, cerebrospinal fluid, or urine of people with Leigh syndrome.

The signs and symptoms of Leigh syndrome are caused in part by patches of damaged tissue (lesions) that develop in the brains of people with this condition. A procedure called magnetic resonance imaging (MRI) reveals characteristic lesions in certain regions of the brain and the brainstem (the part of the brain that is connected to the spinal cord). These regions include the basal ganglia, which help control movement; the cerebellum, which controls the ability to balance and coordinates movement; and the brainstem, which controls functions such as swallowing, breathing, hearing, and seeing. The brain lesions are often accompanied by loss of the myelin coating around nerves (demyelination), which reduces the ability of the nerves to activate muscles used for movement or relay sensory information back to the brain.

How common is Leigh syndrome?
Leigh syndrome affects at least 1 in 40,000 newborns. The condition is more common in certain populations. For example, the condition occurs in approximately 1 in 2,000 newborns in the Saguenay Lac-Saint-Jean region of Quebec, Canada.

Aicardi Syndrome

Aicardi syndrome is a rare neurologic disorder first described by the French neurologist, Dr. Jean Aicardi, in 1965. It occurs almost exclusively in females (46,XX), however, it can also occur in males with Klinfelter Syndrome (47,XXY).  A handful of reports in the literature exist of Aicardi syndrome in a normal male. Some of these reports have been disputed, and it is possible that these cases are caused by mosaic mutations of the Aicardi syndrome gene(s).

What Causes Aicardi Syndrome
The genetic basis or mutation which causes Aicardi syndrome has not been identified despite the efforts of several laboratories worldwide and genetic sequencing of affected children and their parents. Because Aicardi syndrome occurs only in a single member of a family, and virtually all cases are female, the genetic mutation is thought to be a dominant de novo (i.e., spontaneous) mutation in an X-linked gene with lethality in normal (46,XY) males. There are at least 6 sets of twins that are discordant for Aicardi syndrome, and one known set of monozygotic twins and one pair of non-twin sisters that are both affected. Aicardi syndrome in the non-twin sisters is likely due to chance since there have been no other reports of Aicardi syndrome in two siblings.

Features of Aicardi Syndrome
Aicardi syndrome is classically defined in over 90% of cases by three cardinal features:

  • Agenesis (absence of or failed development of a body part) of the corpus callosum
  • Chorioretinal lacunae (punched out lesions in the pigmented layer of the retina)
  • Infantile spasms (a seizure disorder of infancy and early childhood)

In 1999, the diagnostic spectrum of Aicardi syndrome was broadened to include patients with present, but usually abnormal, corpus callosum or absence of infantile spasms or lacunae, if other typical brain abnormalities are present. Specifically, the revised criteria were expanded to include two classic features plus at least two other major or supporting features. Retinal lacunae and seizures are present in all, or almost all, of the cases.  Major and supporting features include:

Major Features

  • Cortical (one of the two types of osseous tissue that form bones) malformations; mostly polymicrogyria (abnormal development of the brain before birth)
  • Periventricular heterotopia (nerve cells [neurons] do not migrate properly during the early development)
  • Subcortical heterotopia (abnormal brain development that is present from birth)
  • Cysts around third cerebral ventricle and/or choroid plexus
  • Papillomas of choroid plexuses (a rare, benign [noncancerous] tumor)
  • Optic disc/nerve coloboma (developmental defect of the eye)

Supporting Features

  • Vertebral and costal (the ribs or the upper sides of the body) abnormalities
  • Microphthalmia or other eye abnormalities
  • “Split-brain” EEG
  • Gross cerebral hemispheric asymmetry.

Involvement of other organ systems besides the brain and eyes are also common but the signs and symptoms are not part of the diagnostic criteria and are not present in all cases. These include:

  • Vascular malformations or vascular malignancy
  • Microcephaly (when a person’s head is significantly smaller than normal for their age & sex)
  • Hypotonia (decreased muscle tone)
  • Spasticity (stiff or rigid muscles)
  • Hypertonia (abnormal increase in muscle tension and a reduced ability of a muscle to stretch)
  • Scoliosis (abnormal curving of the spine)
  • Prominent premaxilla (bilateral cleft lip and palate)
  • Gastroesophageal reflux
  • Feeding problems
  • Small or malformed hands
  • Precocious or delayed puberty
  • Global developmental disabilities

It is generally accepted that the number and severity of features present in a child with Aicardi syndrome is associated with the individual prognosis.