Molecular Genetics and Metabolism 77 (2002) 202–208 www.academicpress.com
Infantile citrullinemia caused by citrin deficiency with increased dibasic amino acids Efrat Ben-Shalom,a Keiko Kobayashi,b Avraham Shaag,a Tomotsugu Yasuda,b Hong-Zhi Gao,b Takeyori Saheki,b Claude Bachmann,c and Orly Elpelega,* a
b
The Metabolic Disease Unit, Faculty of Medicine, Shaare-Zedek Medical Center, Hebrew University, Jerusalem, Israel Department of Biochemistry, Faculty of Medicine, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima 890-8520, Japan c Central Clinical Chemistry Laboratory, University Hospital, 1011 Lausanne, Switzerland Received 18 June 2002; received in revised form 28 August 2002; accepted 29 August 2002
Abstract In an infant who suffered from prolonged icterus and hepatocellular dysfunction we detected an increase of citrulline and dibasic amino acids in plasma and urine. The amino acid levels along with all the abnormal liver tests normalized upon replacing breastmilk by formula feeding; there was no relapse after human milk was tentatively reintroduced. A novel mutation, a 9.5-kb genomic duplication, was identified in the citrin gene (SLC25A13) resulting in the insertion of exon 15. No mutation was detected in the CAT2A specific exon of the SLC7A2 gene which encodes for the liver transporter of cationic amino acids. This is the first report of infantile citrin deficiency in non-Asian patients. Ó 2002 Elsevier Science (USA). All rights reserved. Keywords: Citrin; SLC25A13; Neonatal hepatitis; (Cholestasis, jaundice); Cationic amino acids
1. Introduction A marked increase of citrulline level in blood and urine is characteristic of both classical type I/III (CTLN1; OMIM 215700) and type II citrullinemia (CTLN2; OMIM 603471) [1]. Patients with CTLN1 suffer from recurrent episodes of life-threatening hyperammonemic encephalopathy starting in early infancy and residual neurological damage is common among the survivors. Despite levels of citrulline in plasma exceeding 1000 lmol/L they show no selective over excretion of dibasic amino acids. The enzymatic activity of the urea cycle enzyme argininosuccinate synthetase (ASS) is decreased in all tissues and mutations are found in the ASS gene [1,2]. In contrast, CTLN2 typically presents after the first decade. Patients suffer from a sudden disturbance of consciousness associated with flapping tremor, disorientation, restlessness, drowsiness, and coma, and *
Corresponding author. Fax: +972-2-6523114. E-mail address:
[email protected] (O. Elpeleg).
the majority die within a few years of onset, mainly because of cerebral edema [1]. So far, the disease has only been described in Asian patients [3–6] and a prevalence of 1:100,000 has been estimated in Japan [3]. ASS protein in the liver, but not in other tissues, is markedly decreased though its mRNA is present in normal abundance and there are no mutations in the ASS gene [3,7]. By linkage analysis, Kobayashi et al. [8] identified the responsible gene, SLC25A13, which encodes for citrin, an aspartate/glutamate transporter (AGC) [9]; a carrier rate of 1:70 has been described for the common SLC25A13 mutations in Japan [8,10–12]. Recently, the infantile presentation of citrin deficiency was reported in nine patients [13–16]. These patients were either detected by the neonatal screening for increased galactose or methionine levels in blood or presented with neonatal cholestasis and fatty liver at 1–4 months of age. Accordingly, this presentation was designated NICCD for neonatal intrahepatic cholestasis caused by citrin deficiency (OMIM 605814) [11,15].
1096-7192/02/$ - see front matter Ó 2002 Elsevier Science (USA). All rights reserved. PII: S 1 0 9 6 - 7 1 9 2 ( 0 2 ) 0 0 1 6 7 - 1
E. Ben-Shalom et al. / Molecular Genetics and Metabolism 77 (2002) 202–208
We report the first two non-Asian NICCD patients with an infantile presentation of citrin deficiency due to a novel mutation in the SLC25A13 gene and discuss the accompanying amino acid abnormality.
2. Case report The index case, a 10-week-old male, was admitted for investigation of persistent jaundice. He was the fourth child to consanguineous, first cousin parents of Moslem origin. Pregnancy and birth were unremarkable and birth weight was 3.160 kg. Bilirubin level on the third day of life was 9.1 mg/dL (156 lmol/L); as he was still jaundiced at 8 weeks of age, bilirubin was repeatedly determined and found to be 8.6 mg/dL (148 lmol/L), direct bilirubin 3.2 mg/dL (55 lmol/L). He was exclusively breast-fed and his weight gain and psychomotor development were reportedly normal. On admission he was alert and playful; weight was 5.53 kg and head circumference 39 cm (both at the 25th percentile). The liver was palpable 3 cm below the costal margin. Neurological and ophthalmologic examinations were negative. Abdominal ultrasound revealed an enlarged, homogenous liver and enlarged kidneys (Rt—6 cm, Lt—6.8 cm) with no hydronephrosis. Biochemical investigation disclosed cholestatic disease with alkaline phosphatase 951 U/L, GGT 249 U/L, LDH 844 U/L, total bilirubin 5.9 mg/dL (101 lmol/L), direct bilirubin 0.9 mg/dL (15 lmol/L), AST 77 U/L, ALT 36 U/L, a-fetoprotein 330,000 lg/L, total protein 49 g/L, albumin 24 g/L, fibrinogen 140 mg/dL, PT (INR) 1.39, PTT (ratio) 1.59, ammonia 63 lmol/L, and lactate 2.4 mmol/L. Plasma and urine amino acid analyses revealed increased levels of citrulline, arginine, ornithine, and lysine and a mildly
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decreased fractional tubular reabsorption mainly for lysine (Table 1). Viral hepatitis, tyrosinemia, a1-antitrypsin deficiency, and galactosemia were excluded. In the family, three older brothers were healthy at the time of admission of the index case. The third one (S1 in Fig. 3), a 5-year-old boy had been admitted as infant, at 70 days of age. At that time he had hepatomegaly and cholestatic disease with an increased bilirubin level to 8.4 mg/dL (144 lmol/L), direct 4.3 mg/dL (17 lmol/L), alkaline phosphatase 848 U/L, LDH 817 U/L, GGT 220 U/L, AST 144 U/L, ALT 61 U/L, and a-fetoprotein >35,000 lg=L (the maximal detectable value at the time). As in the index patient there was hypoalbuminemia (24 g/L), low fibrinogen 216 mg/dL, and a mild hyperammonemia 57 lmol/L. Because of high CMV IgM titer, viral hepatitis had been diagnosed. Notably, his urine had been found positive for reducing substances which disappeared after his diet was changed from breast-milk to a cow-milk based formula and remained negative even after breast feeding was reintroduced. Reevaluation at 5 years of age revealed a healthy welldeveloped boy who enjoyed a diversified, qualitatively and quantitatively normal food intake. His laboratory studies at 5 years of age were all normal (total bilirubin 0.4 mg/dL (7 lmol/L), total protein 73 g/L, albumin 42 g/ L, alkaline phosphatase 227 U/L, AST 31 U/L, ALT 19 U/L, GGT 19 U/L, LDH 610 U/L, ammonia 12 lmol/ L, PT INR 0.93, PTT ratio 0.83). Plasma for amino acid analysis was not available but urinary amino acid profile was entirely normal. Because of the gradual aggravation of the amino acid abnormalities in the index case (see Table 1), the increasing blood ammonia level to 82 lM and in view of the favorable effect of switching breast-milk to formula feeding in the brother, the index patientÕs diet was
Table 1 Age (days)
Lysine
Ornithine
Arginine
Citrulline
Plasma amino acids (lM) 71 82 87 90 Breast-fed 4-month-old controls (n ¼ 19)
232 411 235 118 77–218
169 100 174 113 39–136
238 335 170 84 60–134
358 404 44 19 10–29
Urinary amino acids (mmol/mol creatinine) 71 82 87 90 Controls
1004 1179 1089 52
