Hypomyelination

Hypomyelination occurs when myelin production is abnormal, resulting in impaired nerve conduction and the appearance of neurological symptoms, such as tremors.

Symptoms

Symptomatology is variable among dogs, but it is common to appear during the first or second week of life. One of the most characteristic symptoms is tremors, especially in the hind legs, which are accentuated at times of excitement or exercise. In the case of puppies, these tremors can make nursing difficult. In addition, dogs with hypomyelination may show weakness, inability to walk or stand and incoordination.

Disease Management

Unfortunately, there is no cure for canine hypomyelination, and treatment relies on care and support of the affected dog. It is advised to provide assistance during feeding, reduce stress and excitement, and consider physical therapy to improve mobility and coordination.

Genetic basis

This disease follows an autosomal recessive mode of inheritance. Autosomal recessive inheritance means that the dog, regardless of sex, must receive two copies of the mutation or pathogenic variant to be at risk of developing the disease. Both parents of an affected dog must carry at least one copy of the mutation. Animals with only one copy of the mutation are not at increased risk of developing the disease, but may pass the mutation on to future generations. Breeding between dogs carrying genetic variants that can cause disease, even if they do not show symptoms, is not recommended.

Technical report

Myelin is a protective coating that covers the axons of nerve cells and is involved in nerve impulse transmission. Hypomyelination occurs when electrical impulses are interrupted due to a deficiency in myelin production. A mutation in the FNIP2 gene, which encodes folliculin-interacting protein 2, has been linked to the development of hypomyelination. The mutation consists of a deletion of a single A nucleotide, which shifts the reading frame and causes premature incorporation of a translation stop signal. The result is a truncated protein that is believed to cause delayed maturation of a subpopulation of oligodendrocytes (the cell that forms the myelin sheaths of the central nervous system), although the precise function of the FNIP2 gene is not yet fully understood.

Most affected breeds

Weimaraner

Bibliography

Pemberton TJ, Choi S, Mayer JA,et al. A mutation in the canine gene encoding folliculin-interacting protein 2 (FNIP2) associated with a unique disruption in spinal cord myelination. Glia. 2014 Jan;62(1):39-51.