Ayako Tabata

Identification of 13 novel mutations including a retrotransposal insertion in SLC25A13 gene and frequency of 30 mutations found in patients with citrin deficiency.

AbstractDeficiency of citrin, liver-type mitochondrial aspartate-glutamate carrier, is an autosomal recessive disorder caused by mutations of the SLC25A13 gene on chromosome 7q21.3 and has two phenotypes: neonatal intrahepatic cholestatic hepatitis (NICCD) and adult-onset type II citrullinemia (CTLN2). So far, we have described 19 SLC25A13 mutations. Here, we report 13 novel SLC25A13 mutations (one insertion, two deletion, three splice site, two nonsense, and five missense) in patients with citrin deficiency from Japan, Israel, UK, and Czech Republic. Only R360X was detected in both Japanese and Caucasian. IVS16ins3kb identified in a Japanese CTLN2 family seems to be a retrotransposal insertion, as the inserted sequence (2,667-nt) showed an antisense strand of processed complementary DNA (cDNA) from a gene on chromosome 6 (C6orf68), and the repetitive sequence (17-nt) derived from SLC25A13 was found at both ends of the insert. All together, 30 different mutations found in 334 Japanese, 47 Chinese, 11 Korean, four Vietnamese and seven non-East Asian families have been summarized. In Japan, IVS16ins3kb was relatively frequent in 22 families, in addition to known mutations IVS11 + 1G > A, 851del4, IVS13 + 1G > A, and S225X in 189, 173, 48 and 30 families, respectively; 851del4 and IVS16ins3kb were found in all East Asian patients tested, suggesting that these mutations may have occurred very early in some area of East Asia.

Citrin Deficiency: A Novel Cause of Failure to Thrive That Responds to a High-Protein, Low-Carbohydrate Diet

The proband was born at 36 weeks, appropriate for gestational age, to nonconsanguineous white parents. There was no evidence of hyperbilirubinemia or intrahepatic cholestasis in the neonatal period, and she had normal newborn screen results. She presented with 3 episodes of life-threatening bleeding and anemia. The diagnostic evaluation for her bleeding diathesis revealed an abnormal clotting profile with no biochemical evidence for hepatocellular damage. She was incidentally noted to have severe growth deceleration that failed to respond to 502 kJ/kg (120 kcal/kg) per day of protein-hydrolyzed formula. An extensive diagnostic workup for failure to thrive, which was otherwise normal, included plasma amino acid analysis that revealed hyperglutaminemia and citrulline levels within the reference range. Testing of a repeat sample revealed isolated hypercitrullinemia. No argininosuccinic acid was detected. Her ammonia level and urine orotic acid were within the reference ranges. Subsequent plasma amino acid analysis exhibited a profile suggestive of neonatal intrahepatic cholestasis caused by citrin deficiency with elevations in citrulline, methionine, and threonine. Western blotting of fibroblasts demonstrated citrin deficiency, and a deletion for exon 3 was found in the patients coding DNA of the SLC25A13 gene. On the basis of the experience with adults carrying this condition, the patient was given a high-protein, low-carbohydrate diet. The failure to thrive and bleeding diathesis resolved. When compliance with the dietary prescription was relaxed, growth deceleration was again noted, although significant bleeding did not recur. This is the first report of an infant of Northern European descent with citrin deficiency. The later age at presentation with failure to thrive and bleeding diathesis and without obvious evidence of neonatal intrahepatic cholestasis expands the clinical spectrum of citrin deficiency. This case emphasizes the importance of continued dietary control and growth monitoring in children with neonatal intrahepatic cholestasis caused by citrin deficiency and identifies a new metabolic entity responsible for failure to thrive.

Frequency and distribution in East Asia of 12 mutations identified in the SLC25A13 gene of Japanese patients with citrin deficiency

AbstractDeficiency of citrin, a liver-type mitochondrial aspartate-glutamate carrier (AGC), encoded by the SLC25A13 gene on chromosome 7q21.3, causes autosomal recessive disorders: adult-onset type II citrullinemia (CTLN2) and neonatal hepatitis associated with intrahepatic cholestasis (NICCD). So far, we have described 12 SLC25A13 mutations: 11 were from Japan and one from Israel. Three mutations found in Chinese and Vietnamese patients were the same as those in Japanese patients. In the present study, we identified a novel mutation IVS6+1G>C in a Japanese CTLN2 patient and widely screened 12 SLC25A13 mutations found in Japanese patients in control individuals from East Asia to confirm our preliminary results that the carrier frequency was high in Asian populations. Mutations 851-854del and 1638-1660dup were found in all Asian countries tested, and 851-854del associated with 290-haplotype in microsatellite marker D7S1812 was especially frequent. Other mutations frequently detected were IVS11+1G>A in Japanese and Korean, S225X in Japanese, and IVS6+5G>A in Chinese populations. We found a remarkable difference in carrier rates in China (including Taiwan) between north (1/940) and south (1/48) of the Yangtze River. We detected many carriers in Chinese (64/4169 = 1/65), Japanese (20/1372 = 1/69) and Korean (22/2455 = 1/112) populations, suggesting that over 80,000 East Asians are homozygotes with two mutated SLC25A13 alleles.

Pregnancy in a healthy woman with untreated citrullinemia

We report the clinical and biochemical data on a second successful pregnancy in a woman with citrullinemia due to argininosuccinate synthetase deficiency (CTLN1). Despite very elevated plasma and urine citrulline and little or no measurable argininosuccinate synthetase enzyme activity on cultured skin fibroblasts, this 29‐year‐old woman, who was identified through newborn screening, has remained asymptomatic throughout her life. Mutation analysis has recently revealed that she is a compound heterozygote for a known and a novel mutation (IVS15‐1G > C and K310Q, respectively). Many newborn screening programs have recently been expanded to include citrullinemia and numerous asymptomatic hypercitrullinemic infants and children have been identified. It is now important to define prognostic indicators that will help with treatment decisions and genetic counseling for these patients. This patient, as the only citrullinemic adult who has been followed prospectively, contributes important information in this regard. In addition, her child was unaffected by the high citrulline levels demonstrated in amniotic fluid and breast milk suggesting that citrulline is not teratogenic. Although pregnancy is an important risk factor for women with CTLN1, it appears that females with citrullinemia can have normal pregnancy outcomes, as long as metabolic crisis is avoided.