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Disease Profile

Leigh syndrome, French Canadian type

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Cox deficiency, French Canadian type; Cox deficiency, Saguenay Lac saint Jean type; Leigh syndrome, Saguenay Lac saint Jean type;


Congenital and Genetic Diseases; Eye diseases; Metabolic disorders;


The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.

Orpha Number: 70472

Saguenay-Lac-St. Jean (SLSJ) type congenital lactic acidosis, a French Canadian form of Leigh syndrome (see this term), is a mitochondrial disease characterized by chronic metabolic acidosis, hypotonia, facial dysmorphism and delayed development.

The exact prevalence of this disorder is not known. It was first described in Saguenay-Lac-Saint-Jean (Quebec, Canada) where its prevalence at birth is estimated to be 1/2,000. In this region, the prevalence of the gene mutation underlying the disorder is estimated to be 1/23 inhabitants, and may be due to a founder effect.

Clinical description
Facial dysmorphism is characterized by a prominent forehead, wide nasal bridge, hypertelorism, broad anterior fontanelle, midfacial hypoplasia, broad midline, synophrys, and a characteristic arched form of the eyebrows, along with mild hirsutism. There are 3 forms of the disease corresponding to varying degrees of severity: a neonatal form, a classic form and a so-called "survivor" form. The neonatal form is characterized by fulminant acidotic states. The classic form can occur from birth with severe lactic acidosis, or manifest between 14 and 24 months by ataxic gait. This form is associated with episodes of lactic acidosis that can be triggered by physical exertion, emotional stress, infection or a heavy meal, and/or metabolic crises. Patients known as "survivors", i.e. those who have survived several episodes, cross a critical threshold and show less severe symptoms including hypotonia, asthenia, developmental delay (language acquisition and walking) and, in older patients, truncal ataxia, and a characteristic wide-based gait.

SLSJ congenital lactic acidosis is caused by two types of mutations in the LRPPRC gene (2p21). The most frequent is a single A354V mutation. Only one patient has been identified as a heterozygous carrier of the A354V mutation and the C1277Xdel8 deletion of the same gene. LRPPRC codes for the leucine-rich pentatricopeptide repeat-containing protein and appears to be involved in the transport and stability of mature mitochondrial mRNA. Biochemically, the cytochrome C oxidase enzyme (COX) involved in the respiratory chain was found to be deficient in all patients, but other proteins in the respiratory chain may also be deficient.

Diagnostic methods
Diagnosis is based on determination of lactate levels in the blood and cerebrospinal fluid, determination of COX activity in fibroblasts, but is made primarily through identification of the A354V mutation, which confirms the diagnosis.

Differential diagnosis
Differential diagnoses include other forms of Leigh syndrome and other possible causes of metabolic acidosis such as MELAS syndrome, glucose-6-phosphate dehydrogenase (G6PD) deficiency, pyruvate dehydrogenase deficiency, and pyruvate carboxylase deficiency (see these terms).

Antenatal diagnosis
Since the discovery of the underlying mutations in 2003, prenatal diagnosis is offered to couples that have had an affected child.

Genetic counseling
The disease follows a monogenic autosomal recessive pattern of inheritance. Genetic counseling can be proposed to couples at risk through identification of heterozygous carriers.

Management and treatment
There is no specific treatment for the disease. A diet with a balanced intake of proteins, carbohydrates and lipids, spread evenly over the day, is recommended in order to reduce the high energy demands of digestion. Rest and strictly complying with the need for sleep are also beneficial.

In the neonatal form, the prognosis is very poor. In other patients, life expectancy is often less than 5 years due to severe episodes of acidosis.

Visit the Orphanet disease page for more resources.


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
5%-29% of people have these symptoms
Percent of people who have these symptoms is not available through HPO
Anteverted nares
Nasal tip, upturned
Upturned nasal tip
Upturned nose
Upturned nostrils

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Autosomal recessive inheritance
CNS demyelination
Delayed speech and language development
Deficiency of speech development
Delayed language development
Delayed speech
Delayed speech acquisition
Delayed speech development
Impaired speech and language development
Impaired speech development
Language delay
Language delayed
Language development deficit
Late-onset speech development
Poor language development
Speech and language delay
Speech and language difficulties
Speech delay

[ more ]

Failure to thrive
Faltering weight
Weight faltering

[ more ]

Generalized hypotonia
Decreased muscle tone
Low muscle tone

[ more ]

Global developmental delay
Highly arched eyebrow
Arched eyebrows
Broad, arched eyebrows
High, rounded eyebrows
High-arched eyebrows
Thick, flared eyebrows

[ more ]

Excessive hairiness
High blood sugar
Wide-set eyes
Widely spaced eyes

[ more ]

Low blood sugar
Increased CSF lactate
Increased hepatocellular lipid droplets
Increased serum lactate
Infantile onset
Onset in first year of life
Onset in infancy

[ more ]

Lactic acidosis
Increased lactate in body
Low anterior hairline
Low frontal hairline
Low-set frontal hairline

[ more ]

Malar flattening
Zygomatic flattening
Microvesicular hepatic steatosis
Midface retrusion
Decreased size of midface
Midface deficiency
Underdevelopment of midface

[ more ]

Muscular hypotonia
Low or weak muscle tone
Peripheral demyelination
Prominent forehead
Pronounced forehead
Protruding forehead

[ more ]

Psychomotor retardation
Squint eyes

[ more ]

Increased respiratory rate or depth of breathing
Wide nasal bridge
Broad nasal bridge
Broad nasal root
Broadened nasal bridge
Increased breadth of bridge of nose
Increased breadth of nasal bridge
Increased width of bridge of nose
Increased width of nasal bridge
Nasal bridge broad
Wide bridge of nose
Widened nasal bridge

[ more ]



Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.


    Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

    Organizations Supporting this Disease

      Organizations Providing General Support

        Learn more

        These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

        In-Depth Information

        • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
        • The Neuromuscular Disease Center at Washington University provides information about Leigh syndrome.
        • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
        • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
        • PubMed is a searchable database of medical literature and lists journal articles that discuss Leigh syndrome, French Canadian type. Click on the link to view a sample search on this topic.

          Selected Full-Text Journal Articles