Ceroid lipofuscinosis - Neuronal 9 (also known as CLN9) is a rare metabolic disorder that affects the nerve cells of the body and is characterized by the deposits of lipopigments (lipofuscin). Signs and symptoms of the condition generally develop in early childhood (average age 4 years) and may include loss of muscle coordination (ataxia), seizures that do not respond to medications, muscle twitches (myoclonus), visual impairment, and developmental regression (the loss of previously acquired skills). The underlying genetic cause of CLN9 is unknown but it appears to be inherited in an autosomal recessive manner. Treatment options are limited to therapies that can help relieve some of the symptoms.
- Progressive ataxia
- Cerebral atrophy
- Cognitive decline
The aetiology of CLN9 disease is still unknown, but possibly implicated with deficiency in production of a protein that may be a regulator of dihydroceramide synthetase. Hence, CLN9 disease is also termed as CLN9-deficient.
A review conducted by Schulz et.al., 2006, revealed that CLN9-deficient fibroblasts have a distinctive phenotype of rapid growth and increased apoptosis and diminished levels of ceramide, dihydroceramide, and sphingomyelin. Transfection with CLN8 but not other NCL genes corrected growth and apoptosis in CLN9-deficient cells, although the entire CLN8 sequence was normal. CLN8 is one of the TRAM-Lag1-CLN8 proteins containing a Lag1 motif. The latter imparts (dihydro)ceramide synthase activity to yeast cells. Transfection with the yeast gene Lag1 Sc and the human homolog LASS1 increased ceramide levels and partially corrected growth and apoptosis in CLN9-deficient cells. LASS2,-4,,-5, and -6 also corrected growth and apoptosis. Dihydroceramide levels and dihydroceramide synthase activity were markedly diminished in CLN9-deficient cells. Sequencing of LASS1, LASS2, LASS4, LASS5, and LASS6 genes was normal, and expression levels were increased or normal in CLN9-deficient cells by reverse transcription-PCR. N-(4-Hydroxyphenyl)retinamide (4-HPR), a dihydroceramide synthase activator, corrected growth and apoptosis and increased dihydroceramide synthase activity. Ceramide levels dropped further, and there was no increase in de novo ceramide synthesis, probably due to the effects of 4-HPR as activator of dihydroceramide synthase and inhibitor of dihydroceramide desaturase. Fumonisin B1, a dihydroceramide synthase inhibitor, exaggerated the CLN9-deficient phenotype of accelerated growth, decreased ceramide and increased apoptosis. This was neutralized by 4-HPR. The CLN9 protein may be a regulator of dihydroceramide synthase and that 4-HPR could be developed as a treatment for CLN9-deficient patients.
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 resources presented below 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.
Treatment of manifestations: Treatment is currently symptomatic and palliative only. Seizures, malnutrition, gastroesophageal reflux, pneumonia, sialorrhea, depression and anxiety, spasticity, Parkinsonian symptoms, and dystonia can be effectively managed. Antiepileptic drugs (AEDs) should be selected with caution. Benzodiazepines may help control seizures, anxiety, and spasticity. Trihexyphenydate may improve dystonia and sialorrhea. Individuals with swallowing problems may benefit from placement of a gastric (G) tube.
Surveillance: Routine medical management of children and young adults with complex neurodisability will be relevant to all those affected by CLN, and may include surveillance for swallowing difficulties and recurrent aspiration; radiograph surveillance of hip joints and spine.
Agents/circumstances to avoid: Carbamazepine and phenytoin may increase seizure activity and myoclonus and result in clinical deterioration
Genetic counselling: The CLNs are inherited in an autosomal recessive manner with the exception of adult onset, which can be inherited in either an autosomal recessive or an autosomal dominant manner.
Autosomal recessive CLN. The parents of a child with an autosomal recessive form of CLN are obligate heterozygotes, and therefore carry one mutated allele. Heterozygotes have no symptoms. At conception, each sib has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk relatives is possible if the pathogenic variants in the family are known.
Prenatal testing for pregnancies at increased risk is possible if the proband has documented deficient enzyme activity or if the pathogenic variant(s) have been identified in the family.
Schulz, A. (2005). The CLN9 Protein, a Regulator of Dihydroceramide Synthase. Journal of Biological Chemistry, 281(5), pp.2784-2794.