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X-linked Tremor – Springer Spaniel Type
| Acronym: | XLT, SPS |
| Gene: | PLP1 |
| Mutation: | c.110A>C |
| Inheritance: | X-linked recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
X-linked Tremor is a genetic disorder caused by the disruption of the normal myelination of neurons and it has been detected in a few animals including rabbits, pigs, and dogs. It has been reported in a few dog breeds but this type of neurological disorder is specific to Springer Spaniels. The cause of the disease is a mutation, a single base change within the PLP gene encoding proteolipid protein. PLP is believed to play an essential role in the oligodendrocyte differentiation and compaction of the myelin sheath. Oligodendrocytes are terminally differentiated glial cells that form the myelin sheath around axons of the central nervous system (CNS) and their reduction in the number consequently reduces myelin proteins and causes tremor and early death by about 3-4 months of age in the affected dogs.
As the PLP1 gene lies on the X chromosome, tremor caused by dysfunctional myelin formation found in Springer Spaniel dogs shows an X chromosomal recessive mode of inheritance, meaning the specific mutation that causes the disease is located on the sex chromosome. Since male dogs have just one X chromosome, if they carry the mutation, they will develop a bleeding disorder. Female dogs have two X chromosomes and hence, dogs with only one copy of the mutated gene will act as carriers, and dogs carrying both mutated genes will show signs of the disease. Early genetic testing can help identify dogs that carry the gene with the specific mutation and prevent their further breeding by the proper selection of mating pairs.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (female) or hemizygous state (male) (i.e. only healthy allele on X chromosome). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has mutated allele in homozygous state (female) or hemizygous state (male) (i.e. only mutated allele on X chromosome). It is likely the animal will experience a genetic disorder due to this mutation.**It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Penetrance of tested mutation, and potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Nadon, N. L., Duncan, I. D., Hudson, L. D. (1990). A point mutation in the proteolipid protein gene of the shaking pup interrupts oligodendrocyte development. Development (Cambridge, England), 110(2), 529–537. https://doi.org/10.1242/dev.110.2.529
Griffiths, I. R., Duncan, I. D., McCulloch, M., Harvey, M. J. (1981). Shaking pups: a disorder of central myelination in the Spaniel dog. Journal of the neurological sciences, 50(3), 423–433. https://doi.org/10.1016/0022-510x(81)90154-4