Cystinuria type B is a congenital metabolic defect that causes abnormal amino acid transport in the intestine and kidneys, leading to urolithiasis and cystine crystal formation. This disorder has been linked to different variants in the SLC7A9 gene, which encodes a subunit of an amino acid transporter.
Symptoms
Clinical signs of cystinuria usually appear around 3 to 4 years of age, although in some cases they are documented as early as two months of age. One of the main clinical features is the presence of cystine crystals in the urine, although elevated levels of other amino acids such as ornithine, lysine and arginine are also observed. In addition, affected cats show signs of lower urinary tract disease, including hematuria, oliguria and straining to urinate with frequent attempts.
Disease Management
The management of cystinuria focuses on the elimination or dissolution of the uroliths through dietary changes and medical treatment. A low-protein, low-sodium diet with a high water content is recommended.
Genetic basis
This disease follows an autosomal recessive mode of inheritance. Autosomal recessive inheritance means that the cat, regardless of sex, must receive two copies of the mutation or pathogenic variant to be at risk of developing the disease. Both parents of an affected cat must carry at least one copy of the mutation. Animals with only one copy of the mutation are not at increased risk of developing the disease, but may pass the mutation on to future generations. Breeding between cats carrying genetic variants that may cause disease, even if they do not show symptoms, is not recommended.
Technical report
Cystinuria is a congenital metabolic defect that affects the renal proximal tubule, hindering the reabsorption of amino acids such as cystine, ornithine, lysine and arginine. This condition causes the formation of uroliths and urinary obstructions. Feline cystinuria was first reported in 1991. A variant in the SLC7A9 gene associated with cystinuria was identified in the Maine Coon, Siamese and Sphynx breeds. The SLC7A9 gene encodes a protein that is part of a plasma membrane transporter involved in the reabsorption of basic amino acids and cystine in the kidney and intestine. The c.881T>A variant in SLC7A9 causes the substitution of a hydrophobic valine for a hydrophilic glutamic acid, affecting the function of the amino acid transporter. Other variants have been described in the same gene, such as c.706G>A and c.1175C>T, related to the development of cystinuria in other feline lines.
Most affected breeds
Domestic Longhair
Maine Coon
Siamese
Siberian
Sphynx
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