Neuronal ceroid lipofuscinoses (NCLs) represent the most common group of inherited progressive encephalopathies in children. They are characterized by progressive loss of vision, mental and motor deterioration, epileptic seizures, and premature death. Rare adult forms of NCL with late onset are known as Kufs’ disease. Loci underlying these adult forms remain unknown due to the small number of patients and genetic heterogeneity. Here we confirm that a late-onset form of NCL recessively segregates in US and French pedigrees of American Staffordshire Terrier (AST) dogs. Through combined association, linkage, and haplotype analyses, we mapped the disease locus to a single region of canine chromosome 9. We eventually identified a worldwide breed-specific variant in exon 2 of the Arylsulfatase G ( ARSG ) gene, which causes a p.R99H substitution in the vicinity of the catalytic domain of the enzyme. In transfected cells or leukocytes from affected dogs, the missense change leads to a 75% decrease in sulfatase activity, providing a functional confirmation that the variant might be the NCL-causing mutation. Our results uncover a protein involved in neuronal homeostasis, identify a family of candidate genes to be screened in patients with Kufs' disease, and suggest that a deficiency in sulfatase is part of the NCL pathogenesis.

Erythropoietic protoporphyria (EPP) (MIM 177000) is an inherited disease due to partial deficiency of ferrochelatase (FECH; EC 4.99.1.1.), the last enzyme in the heme biosynthetic pathway. FECH is located on the mitochondrial inner membrane and catalyzes the insertion of ferrous iron into protoporphyrin IX (PPIX) to form heme. Chronic, progressive, and irreversible cholestatic liver failure occurs in about 3% of EPP patients and results in the need for liver transplantation.¹ x 1 Schneider-Yin, X., Gouya, L., Meier-Weinand, A. et al. New insights into the pathogenesis of erythropoietic protoporphyria and their impact on patient care. Eur J Pediatr. 2000; 159: 719–725 Crossref | PubMed | Scopus (52) | Google Scholar See all References Although EPP is generally an indolent disease manifested mainly by photosensitivity, biochemical evidence of liver dysfunction may occur in 10% to 20% of patients. Many patients with EPP develop gallstones containing PPIX (for review see Puy et al² x 2 Puy, H., Gouya, L., and Deybach, J.C. Porphyrias. Lancet. 2010; 375: 924–937 Abstract | Full Text | Full Text PDF | PubMed | Scopus (299) | Google Scholar See all References ). The mode of inheritance of EPP is complex, with incomplete penetrance of the disease and considerable variability in clinical expression.³ x 3 Gouya, L., Martin-Schmitt, C., Robreau, A.M. et al. Contribution of a common single-nucleotide polymorphism to the genetic predisposition for erythropoietic protoporphyria. Am J Hum Genet. 2006; 78: 2–14 Abstract | Full Text | Full Text PDF | PubMed | Scopus (116) | Google Scholar See all References FECH deficiency in bone marrow erythroid cells is responsible for a mild microcytic anemia.⁴ x 4 Delaby, C., Lyoumi, S., Ducamp, S. et al. Excessive erythrocyte PPIX influences the hematologic status and iron metabolism in patients with dominant erythropoietic protoporphyria. Cell Mol Biol (Noisy-le-grand). 2009; 55: 45–52 PubMed | Google Scholar See all References Accumulation of PPIX in bone marrow erythroid cells leads to high levels of PPIX in plasma, skin, bile, and feces.⁴ x 4 Delaby, C., Lyoumi, S., Ducamp, S. et al. Excessive erythrocyte PPIX influences the hematologic status and iron metabolism in patients with dominant erythropoietic protoporphyria. Cell Mol Biol (Noisy-le-grand). 2009; 55: 45–52 PubMed | Google Scholar See all References ^{, 5} x 5 Lyoumi, S., Abitbol, M., Andrieu, V. et al. Increased plasma transferrin, altered body iron distribution, and microcytic hypochromic anemia in ferrochelatase-deficient mice. Blood. 2007; 109: 811–818 Crossref | PubMed | Scopus (45) | Google Scholar See all References PPIX is a hydrophobic compound and is removed from the body via the liver where it is secreted into the bile and eliminated in the feces. Accumulation of PPIX in the liver causes cholestasis and liver fibrosis.

Patients with deficiency in ferrochelatase (FECH), the last enzyme of the heme biosynthetic pathway, experience a painful type of skin photosensitivity called erythropoietic protoporphyria (EPP), which is caused by the excessive production of protoporphyrin IX (PPIX) by erythrocytes. Controversial results have been reported regarding hematologic status and iron status of patients with EPP. We thoroughly explored these parameters in Fech^m1Pas mutant mice of 3 different genetic backgrounds. FECH deficiency induced microcytic hypochromic anemia without ringed sideroblasts, little or no hemolysis, and no erythroid hyperplasia. Serum iron, ferritin, hepcidin mRNA, and Dcytb levels were normal. The homozygous Fech^m1Pas mutant involved no tissue iron deficiency but showed a clear-cut redistribution of iron stores from peripheral tissues to the spleen, with a concomitant 2- to 3-fold increase in transferrin expression at the mRNA and the protein levels. Erythrocyte PPIX levels strongly correlated with serum transferrin levels. At all stages of differentiation in our study, transferrin receptor expression in bone marrow erythroid cells in Fech^m1Pas was normal in mutant mice but not in patients with iron-deficiency anemia. Based on these observations, we suggest that oral iron therapy is not the therapy of choice for patients with EPP and that the PPIX–liver transferrin pathway plays a role in the orchestration of iron distribution between peripheral iron stores, the spleen, and the bone marrow.

Seven donkey breeds are recognized by the French studbook. Individuals from the Pyrenean, Provence, Berry Black, Normand, Cotentin and Bourbonnais breeds are characterized by a short coat, while those from the Poitou breed (Baudet du Poitou) are characterized by a long-hair phenotype. We hypothesized that loss-of-function mutations in the FGF5 (fibroblast growth factor 5) gene, which are associated with a long-hair phenotype in several mammalian species, may account for the special coat feature of Poitou donkeys. To the best of our knowledge, mutations in FGF5 have never been described in Equidae. We sequenced the FGF5 gene from 35 long-haired Poitou donkeys, as well as from a panel of 67 short-haired donkeys from the six other French breeds and 131 short-haired ponies and horses. We identified a recessive c.433_434delAT frameshift deletion in FGF5, present in Poitou and three other donkey breeds and a recessive nonsense c.245G > A substitution, present in Poitou and four other donkey breeds. The frameshift deletion was associated with the long-hair phenotype in Poitou donkeys when present in two copies (n = 31) or combined with the nonsense mutation (n = 4). The frameshift deletion led to a stop codon at position 159 whereas the nonsense mutation led to a stop codon at position 82 in the FGF5 protein. In silico, the two truncated FGF5 proteins were predicted to lack the critical β strands involved in the interaction between FGF5 and its receptor, a mandatory step to inhibit hair growth. Our results highlight the allelic heterogeneity of the long-hair phenotype in donkeys and enlarge the panel of recessive FGF5 loss-of-function alleles described in mammals. Thanks to the DNA test developed in this study, breeders of non-Poitou breeds will have the opportunity to identify long-hair carriers in their breeding stocks.