The ceroid-lipofuscinoses are a group of inherited neurodegenerative diseases of human beings and animals characterised histologically by the accumulation of a fluorescent lipopigment in neurons and many other cells within the body.
NCL has been reported in dogs, cats, cattle and sheep. In sheep, it has been recorded in South Hampshire (NZ), Rambouillet (Texas) and Swedish Landracc Lambs.
This is a report of NCL in Merino sheep on a property in New South Wales.
In May 1997, the owner of a commercial fine wool flock (500 breeding ewes) sought advice on a case of suspected blindness in a 10 month old hogget within the group of August/September 1997 drop lambs. Six similar cases had occurred in 1996 (a total of 9 cases subsequently occurred in 1997). The paddocks were clean, and the sheep were drenched under the Wormkill program.
First signs occurred at about 9 months of age They included a decreased menace response (affected lambs approach an observer or dog rather than move away; they follow a sound source and may bleat like a young lamb). They appeared to be visually impaired, and held the head low, but would baulk at gateways and fences. Later they appeared unaware of their environment, standing at the edge of, or apart from the mob. The first detection of an affected animal was often at this later stage, with the animal appearing blind. As mental status progressively deteriorated, signs include repetitive activities (walking in circles in a confined place, grinding of teeth), somnolence, and central blindness. Death usually occurred from misadventure, or affected animals were killed on humane grounds.
The cerebral hemispheres were smaller and firmer than normal and the gyre were thin. The brain weighed 70-80 gm (normal is 110-120 gm). On section the cerebral cortex was half the normal depth.
Microscopic features comprised severe cerebrocortical atrophy with marked astrocytosis, and the presence of eosinophilic intracytoplasmic inclusions in neurons, hepatocytes and renal cortical tubular epithelium. These inclusions have staining characteristics of "lipofuscin", but are predominantly composed of a highly hydrophobic protein (subunit c of mitochondrial ATP synthase).
Retinal degeneration involving the photoreceptor layers was a late development Affected animals first became centrally blind from the severe cerebrocortical atrophy.
How did it come about?
The 12 new rams introduced to the breeding flock during the previous five years had been purchased from the same stud. The rate of retention of ewe lambs for breeding was high, and ewes were bred only three times before replacement at five years of age. The chances of sire-daughter matings were further increased as no new rams were introduced for the 1995 and 1996 joinings. It is likely that more than one carrier ram has been involved.
Where to now?
Studies are in progress to determine if NCL in Merino and South Hampshire sheep is caused by the same genetic mutation. These studies include the establishment, at the University of Sydney, of a small breeding flock of Merino sheep carrying the defect. When genetic markers of NCL in Merino sheep are determined, tests can then be developed to survey the prevalence of the defect in the breed, and to test stud animals for certification.