Neuronal ceroid lipofuscinosis 7 (NCL7 or CLN7) is a neurodegenerative lysosomal storage disease with autosomal recessive inheritance caused by variants in the MFSD8 (CLN7) gene. It was first described in the Chinese Crested and the same variant has been documented in the Chihuahua. It produces progressive neurological deterioration with vision loss, cognitive and behavioural alterations, and ultimately becomes lethal; there is no curative treatment.

Documented in the Chinese Crested (first description) and in the Chihuahua. In a screening of Chihuahuas in Japan, a carrier rate of approximately 1.29% was found (allele frequency ~0.0065). There are no reliable frequency data in other breeds or other populations.

- Progressive neurological deterioration\n- Blindness and vision loss\n- Anxiety and behavioural alterations\n- Cognitive impairment\n- Ataxia and gait alterations\n- Myoclonus and, in advanced stages, seizures\n- Weight loss and premature death

The variant was identified in 2015 by whole-genome sequencing of a Chinese Crested (Guo et al., 2015). In the following years the same deletion was confirmed in Chihuahuas from different countries (Faller et al., 2016; Karli et al., 2016; Ashwini et al., 2016), which makes the Chihuahua a valid reference breed alongside the Chinese Crested. In 2022 a population screening in Chihuahuas from Japan was published. MFSD8 encodes a lysosomal protein and human variants cause CLN7 Batten disease, hence the interest in the dog as a model.

- Genotype breeding dogs, especially in the Chinese Crested and Chihuahua\n- Do not mate two carriers: 25% of the offspring would be affected homozygotes\n- A carrier can be mated to a clear individual; test offspring intended for breeding\n- Exclude affected homozygotes from breeding\n- In the event of a confirmed case, do not repeat the parental mating and inform the owners of the status

The differential diagnosis includes other canine neuronal ceroid lipofuscinoses (caused by CLN8, PPT1, TPP1, etc.) and other neurodegenerative diseases; the clinical presentation and MRI guide the diagnosis, but definitive confirmation is molecular. Pathological diagnosis shows intracellular accumulation of autofluorescent material in the brain and cerebellum. As it is a lethal disease with no treatment, genetic counselling and carrier testing are the only effective measure.

1. Guo J et al. 2015. A rare homozygous MFSD8 single-base-pair deletion and frameshift in the whole genome sequence of a Chinese Crested dog with neuronal ceroid lipofuscinosis. BMC Vet Res. PMID: 25551667
2. Faller KM et al. 2016. The Chihuahua dog: A new animal model for neuronal ceroid lipofuscinosis CLN7 disease? J Neurosci Res. PMID: 26762174
3. Karli P et al. 2016. MFSD8 single-base pair deletion in a Chihuahua with neuronal ceroid lipofuscinosis. Anim Genet. PMID: 27145727
4. Ashwini A et al. 2016. Neuronal ceroid lipofuscinosis associated with an MFSD8 mutation in Chihuahuas. Mol Genet Metab. PMID: 27211611
5. Pervin S et al. 2022. Screening and Carrier Rate of Neuronal Ceroid Lipofuscinosis in Chihuahua Dogs in Japan. Animals (Basel). PMID: 35565635
OMIA001962-9615.