Cloning of the canine gene encoding transcription factor Pit-1 and its exclusion as candidate gene in a canine model of pituitary dwarfism

Isolated growth hormone deficiency in a Chihuahua with a GH1 mutation

A 6-mo-old female Chihuahua was presented with recurrent episodes of hypoglycemia and collapse. Physical examination revealed proportionate dwarfism, retained puppy hair coat, retained deciduous teeth, and open fontanelles. Routine blood tests revealed hypoglycemia, thrombocytosis, hypoproteinemia, and elevated alkaline phosphatase activity. The urinalysis, radiographs, and ultrasonographs were unremarkable. Endocrine testing revealed that insulin-like growth factor 1 was below the detection limit; concentrations of total thyroxine, baseline cortisol, and cortisol stimulated by tetracosactide acetate were within their reference intervals. The pituitary gland showed no organic abnormalities on magnetic resonance imaging. For definitive diagnosis, we conducted the stimulation test for growth hormone (GH) release and diagnosed isolated GH deficiency. Genetic investigation revealed that the present case had 4 point mutations in intronic regions and a 6-bp deletion in exon 5 of GH1. The bioinformatics tool PROVEAN algorithm predicted that the deletion in exon 5 could be deleterious to the function of GH1.

GH deficiency in a Dalmatian puppy with megaesophagus

An 8 wk old female Dalmatian weighing .56 kg presented with growth retardation. The puppy exhibited no abnormalities during physical examination other than significantly reduced growth compared with her littermates. Endocrine results suggested pituitary dwarfism. Two wk later, the puppy returned due to the onset of megaesophagus, but the puppy unfortunately died the following morning. This case report describes the diagnosis of dwarfism in a Dalmatian puppy that was caused by growth hormone (GH) deficiency and describes its early clinical manifestations.

Genome-wide association studies for multiple diseases of the German Shepherd Dog

The German Shepherd Dog (GSD) is a popular working and companion breed for which over 50 hereditary diseases have been documented. Herein, SNP profiles for 197 GSDs were generated using the Affymetrix v2 canine SNP array for a genome-wide association study to identify loci associated with four diseases: pituitary dwarfism, degenerative myelopathy (DM), congenital megaesophagus (ME), and pancreatic acinar atrophy (PAA). A locus on Chr 9 is strongly associated with pituitary dwarfism and is proximal to a plausible candidate gene, LHX3. Results for DM confirm a major locus encompassing SOD1, in which an associated point mutation was previously identified, but do not suggest modifier loci. Several SNPs on Chr 12 are associated with ME and a 4.7 Mb haplotype block is present in affected dogs. Analysis of additional ME cases for a SNP within the haplotype provides further support for this association. Results for PAA indicate more complex genetic underpinnings. Several regions on multiple chromosomes reach genome-wide significance. However, no major locus is apparent and only two associated haplotype blocks, on Chrs 7 and 12 are observed. These data suggest that PAA may be governed by multiple loci with small effects, or it may be a heterogeneous disorder.

A contracted DNA repeat in LHX3 intron 5 is associated with aberrant splicing and pituitary dwarfism in German shepherd dogs

Dwarfism in German shepherd dogs is due to combined pituitary hormone deficiency of unknown genetic cause. We localized the recessively inherited defect by a genome wide approach to a region on chromosome 9 with a lod score of 9.8. The region contains LHX3, which codes for a transcription factor essential for pituitary development. Dwarfs have a deletion of one of six 7 bp repeats in intron 5 of LHX3, reducing the intron size to 68 bp. One dwarf was compound heterozygous for the deletion and an insertion of an asparagine residue in the DNA-binding homeodomain of LHX3, suggesting involvement of the gene in the disorder. An exon trapping assay indicated that the shortened intron is not spliced efficiently, probably because it is too small. We applied bisulfite conversion of cytosine to uracil in RNA followed by RT-PCR to analyze the splicing products. The aberrantly spliced RNA molecules resulted from either skipping of exon 5 or retention of intron 5. The same splicing defects were observed in cDNA derived from the pituitary of dwarfs. A survey of similarly mutated introns suggests that there is a minimal distance requirement between the splice donor and branch site of 50 nucleotides. In conclusion, a contraction of a DNA repeat in intron 5 of canine LHX3 leads to deficient splicing and is associated with pituitary dwarfism.

The leukemia inhibitory factor receptor gene is not involved in the etiology of pituitary dwarfism in German shepherd dogs

Pituitary dwarfism in German shepherd dogs is characterized by combined pituitary hormone deficiency (CPHD) and intrapituitary cyst formation. Activation of the leukemia inhibitory factor (LIF)-LIF receptor (LIFR) signal transduction pathway results in a similar phenotype in (transgenic) mice. We therefore assessed the role of the LIFR in the etiology of pituitary dwarfism in German shepherd dogs. A polymorphic microsatellite marker (UULIFR) was used to analyze the segregation of the LIFR gene in 22 German shepherd dogs from 4 pedigrees, each including one dwarf. There was no allelic association between UULIFR and the dwarfism phenotype. Based on our findings LIFR was excluded as a candidate gene for CPHD.

Ghrelin-stimulation test in the diagnosis of canine pituitary dwarfism

This study investigated whether ghrelin, a potent releaser of growth hormone (GH) secretion, is a valuable tool in the diagnosis of canine pituitary dwarfism. The effect of intravenous administration of ghrelin on the release of GH and other adenohypophyseal hormones was investigated in German shepherd dogs with congenital combined pituitary hormone deficiency and in healthy Beagles. Analysis of the maximal increment (i.e. difference between pre- and maximal post-ghrelin plasma hormone concentration) indicated that the GH response was significantly lower in the dwarf dogs compared with the healthy dogs. In none of the pituitary dwarfs, the ghrelin-induced plasma GH concentration exceeded 5 microg/l at any time. However, this was also true for 3 healthy dogs. In all dogs, ghrelin administration did not affect the plasma concentrations of ACTH, cortisol, TSH, LH and PRL . Thus, while a ghrelin-induced plasma GH concentration above 5 microg/l excludes GH deficiency, false-negative results may occur.

Ovis aries POU1F1 Gene: Cloning, Characterization and Polymorphism Analysis

POU1F1 (PIT-1/GHF-1) is a transcription factor with critical role in the transcriptional regulation of multiple genes in the pituitary and also important for the survival, differentiation and proliferation of three pituitary cell types. To understand the regulation of POU1F1 gene in Ovis aries we report its cloning, sequencing and characterization. The sequenced 5787 bp included six exons and two complete introns. Ovine POU1F1 gene has a high level of conservation with its bovine, human and rat counterparts showing 98.2%, 91.2% and 86.2% of similarity at the coding level, respectively. All six exons were analyzed for polymorphism detection in 100 animals of the Portuguese indigenous ovine breed 'Churra da Terra Quente'. One polymorphism was found at codon 58 in exon 2, in one allele of 4 animals leading to a change from cysteine to tyrosine (2% allelic frequency). In exon 3 two polymorphisms were detected: a G to A transition altering a glycine to an asparagine at codon 89 in one allele of one animal (0.5% allelic frequency) and another G to A transition at codon 105 converting an alanine into a threonine in one allele of 3 animals (1.5% allelic frequency). These polymorphisms might change the structure of the POU1F1 protein and modify gene-expression. In intron 4, an A to G transition was detected in one allele of six animals (3% allelic frequency). Exons 1, 4 and 6 showed no polymorphisms.

Endocrine diseases in dogs and cats: similarities and differences with endocrine diseases in humans

Over several millennia, humans have created hundreds of dog and cat breeds by selective breeding, including fixation of mutant genes. The domestic dog is unique in the extent of its variation in height, weight and shape as well as its behavior. It is primarily the relatively long persistence of high levels of growth hormone (GH) release at a young age that accounts for the large body size in giant breeds of dogs. Several of the endocrine diseases of humans are also known to occur as similar entities in dogs and cats. With some variations, this is true for conditions such as diabetes mellitus and the hypofunction syndromes of the thyroid and adrenal cortex. Also, the hyperfunction syndromes of hypercortisolism and hyperparathyroidism in dogs and cats have many similarities with their human counterparts. The exception seems to be Graves' disease. This condition, which is due to production of thyroid-stimulating hormone (TSH)-receptor antibodies, has not been observed in dogs and cats. The very common form of hyperthyroidism in cats is due to toxic adenomas. In the 1980s it was discovered that in dogs exogenous progestins and endogenous progesterone can induce GH excess. This GH excess originates form the mammary gland and may give rise to acromegaly and insulin resistance. GH production by the mammary gland is not unique to the dog. It has become clear that cats and humans also express the GH gene in the mammary gland. There is increasing evidence that this locally produced GH not only plays a role in the morphologic changes of the mammary gland associated with the ovarian cycle and gestation, but that it is also involved in the development of breast cancer. In dogs, induction of mammary GH production by progestin administration allows for treatment of GH deficiency.

Exclusion of the lim homeodomain gene LHX4 as a candidate gene for pituitary dwarfism in German shepherd dogs

Pituitary dwarfism in the German shepherd dog is an autosomal recessive inherited abnormality. We tested the hypothesis that a variant of the LIM homeodomain gene LHX4 is responsible for the dwarfism phenotype. To this end, we isolated Bacterial Artificial Chromosome clones for the canine LHX4 gene. Southern blotting experiments showed that the LHX4 gene is a single copy gene in the canine genome. A complex CA-repeat was isolated from the BAC clones and was found to be polymorphic in German shepherd dogs. Genotyping 5 litters in which the dwarfism was segregating showed disconcordance between the inheritance of the dwarfism phenotype and the DNA marker. It is concluded that the LHX4 gene does not play a primary role in the pituitary dwarfism in the German shepherd dogs.

Chromosome-specific single-locus FISH probes allow anchorage of an 1800-marker integrated radiation-hybrid/linkage map of the domestic dog genome to all chromosomes

We present here the first fully integrated, comprehensive map of the canine genome, incorporating detailed cytogenetic, radiation hybrid (RH), and meiotic information. We have mapped a collection of 266 chromosome-specific cosmid clones, each containing a microsatellite marker, to all 38 canine autosomes by fluorescence in situ hybridization (FISH). A 1500-marker RH map, comprising 1078 microsatellites, 320 dog gene markers, and 102 chromosome-specific markers, has been constructed using the RHDF5000-2 whole-genome radiation hybrid panel. Meiotic linkage analysis was performed, with at least one microsatellite marker from each dog autosome on a panel of reference families, allowing one meiotic linkage group to be anchored to all 38 dog autosomes. We present a karyotype in which each chromosome is identified by one meiotic linkage group and one or more RH groups. This updated integrated map, containing a total of 1800 markers, covers >90% of the dog genome. Positional selection of anchor clones enabled us, for the first time, to orientate nearly all of the integrated groups on each chromosome and to evaluate the extent of individual chromosome coverage in the integrated genome map. Finally, the inclusion of 320 dog genes into this integrated map enhances existing comparative mapping data between human and dog, and the 1000 mapped microsatellite markers constitute an invaluable tool with which to perform genome scanning studies on pedigrees of interest.

Combined pituitary hormone deficiency in german shepherd dogs with dwarfism

In German shepherd dogs pituitary dwarfism is known as an autosomal recessive inherited abnormality. To investigate whether the function of cells other than the somatotropes may also be impaired in this disease, the secretory capacity of the pituitary anterior lobe (AL) cells was studied by a combined pituitary AL stimulation test with four releasing hormones (4RH test) in four male and four female German shepherd dwarfs. In addition, the morphology of the pituitary was investigated by computed tomography. The physical features of the eight German shepherd dwarfs were primarily characterized by growth retardation and stagnant development of the hair coat. The results of the 4RH test confirmed the presence of hyposomatotropism. The basal plasma TSH and prolactin concentrations were also low and did not change upon stimulation. Basal plasma concentrations of LH were relatively low and responded only slightly to suprapituitary stimulation. With respect to the plasma FSH levels there was a clear gender difference. In the males plasma FSH concentrations remained below the detection limit throughout the 4RH test, whereas in the females the basal plasma FSH levels were slightly lower and there was only a small increase following suprapituitary stimulation, compared with the values in age-matched controls. In contrast, basal and stimulated plasma ACTH concentrations did not differ between the dwarfs and the controls. Computed tomography of the pituitary fossa revealed a normal sized pituitary with cysts in five dogs, an enlarged pituitary with cysts in two dogs, and a small pituitary gland without cysts in the remaining dog. The results of this study demonstrate that German shepherd dwarfs have a combined deficiency of GH, TSH, and prolactin together with impaired release of gonadotropins, whereas ACTH secretion is preserved. The combined pituitary hormone deficiency is associated with cyst formation and pituitary hypoplasia.

Bone disorders in the dog: a review of modern genetic strategies to find the underlying causes

In man, the genetic defects of more than 600 inherited diseases, of which at least 150 skeletal diseases, have been identified as is the chromosomal location for approximately 7000 genes. This rapid progress has been made possible by the generation of a genetical and physical map of the human genome. There is no reason to believe that for the dog not a similar development may occur. This review is therefore focussed on the use of novel tools now available for comparative molecular genetic studies of skeletal dysplasias in the dog. Because the genomes of mammals at the subchromosomal level are very well conserved, likely candidate disease genes known from other species might be considered. In this review, formation of the bones and the most important canine disorders of the skeleton influencing locomotion will be discussed first. The canine disorders discussed are canine hip dysplasia, the three different forms of elbow dysplasia (fragmented coronoid process, ununited anconeal process, osteochondrosis dissecans and incongruency) and dwarfism. Where possible a link is made with similar diseases in man or mouse. Then, the molecular biological tools available to analyse the genetic defect will be reviewed and some examples discussed.