Lipid storage disease in 4 sibling superb birds-of-paradise (Lophorina superba)

Abstract

Pedigree analysis, clinical, gross, microscopic, ultrastructural, and lipidomic findings in 4 female superb bird-of-paradise (SBOP, Lophorina superba) siblings led to the diagnosis of a primary inherited glycerolipid storage disease. These birds were the offspring of a related breeding pair (inbreeding coefficient = 0.1797) and are the only known SBOPs to display this constellation of lesions. The birds ranged from 0.75 to 4.3 years of age at the time of death. Two birds were euthanized and 1 died naturally due to the disease, and 1 died of head trauma with no prior clinical signs. Macroscopic findings included hepatomegaly and pallor (4/4), cardiac and renal pallor (2/4), and coelomic effusion (1/4). Microscopic examination found marked tissue distortion due to cytoplasmic lipid vacuoles in hepatocytes (4/4), cardiomyocytes (4/4), renal tubular epithelial cells (4/4), parathyroid gland principal cells (2/2), exocrine pancreatic cells (3/3), and the glandular cells of the ventriculus and proventriculus (3/3). Ultrastructurally, the lipids were deposited in single to coalescing or fused droplets lined by an inconspicuous or discontinuous monolayer membrane. Lipidomic profiling found that the cytoplasmic lipid deposits were primarily composed of triacylglycerols. Future work, including sequencing of the SBOP genome and genotyping, will be required to definitively determine the underlying genetic mechanism of this disease.

Keywords: Lophorina superba; bird-of-paradise; lipid; lipidomics; pathology; storage disease.

Figure 1.

Pedigree of four superb bird-of-paradise siblings with a multisystemic lipid storage disease (labeled 1–4). Circles represent females, black squares represent males, and diamonds represent undetermined sex; X indicates unaffected, deceased birds. Birds with no parentage are founder birds collected from the wild.

Figure 2.

Gross and microscopic features of a multisystemic lipid storage disease in sibling superb birds-of-paradise. a) Coelomic cavity. The heart and liver are pale tan and the liver is massively enlarged with rounded edges. Case 4. b) Liver. Hepatocytes are diffusely expanded by round, clear, intracytoplasmic vacuoles consistent with lipid, which displace the nucleus. Central veins are surrounded by few hematopoietic cells. Case 4. Hematoxylin and eosin (HE). c) Liver. Hepatocellular cytoplasmic vacuoles diffusely stain red. Case 4. Oil red-O. d) Heart. Cardiomyocytes throughout the thickness of the atrium and ventricle are diffusely expanded by lipid vacuoles. Case 1. HE. e) Heart. Cardiomyocyte vacuoles disrupt the myofibers. Case 1. HE. Inset: Cardiomyocyte vacuoles stain red. Case 4. Oil red-O.

Figure 3.

Ultrastructural features of a multisystemic lipid storage disease in sibling superb birds-of-paradise. a) Hepatocytes. Individual and coalescing, up to 18 nm diameter, lipid droplets (Ld) expand the cytoplasm and displace organelles, including the nucleus (N). Clear spaces around lipid droplets are occupied by soluble glycogen (black chevron). Scale bar is 10 μm. b) Hepatocytes. Lipids droplets (Ld) are in contact with beta-glycogen particles (G) and mitochondria (M). Scale bar is 2 μm. Case 4. c) Cardiomyocytes. Sarcoplasmic accumulation of individual and coalescing or fused lipid droplets (Ld). Myofibrils (Mf) are disarrayed or disrupted, and mitochondria (M) are displaced by accumulation of large lipid droplets. Intercalated disc = white chevron. Scale bar is 5 μm. d) Cardiomyocyte. A lipid droplet with inconspicuous monolayer membrane (white arrowheads) is in contact with mitochondria, one of which is distended by beta glycogen particles (G). Mitochondrion cristae are numerous and displaced (MC). Scale bar is 1 μm. e) Cardiomyocyte. A lipid droplet (Ld) displaying a monolayered membrane in contact with the myofilaments (mf) comprising a myofibril. Scale bar is 0.5 μm. Case 4.

Figure 4.

Charts showing proportions of the major categories of lipids comprising the lipidome of tissues from control superb birds-of paradise (control liver, n=2) and siblings affected by a multisystemic lipid storage disease (affected liver, n=3; affected heart, n=2). Acylcarnitines were present at levels of < 0.01% in all tissues.