Citrin Deficiency

Case of YKHPIY is an 8-year-old Japanese female who presented with a known diagnosis to our genetics clinic.

She was born at 39 weeks via C-section for failure to progress. Her mother was induced secondary to IUGR and oligohydramnios. She weighed 2416g (A and c.851-854del) account for the majority (~70%) of pathologic alleles in Japanese persons with citrin deficiency.

Only one mutation, p.Arg360X, has been found in both Japanese and Northern European populations

Manifestations of citrin deficiencyNeonatal intrahepatic cholestasis (NICCD)

Failure to thrive and dyslipidemia in older children (FTTDCD)

Recurrent hyperammonemia with neuropsychiatric symptoms in adults (CTLN2)These manifestations are the only phenotypes currently known to be associated with mutations in SLC25A1315

As you can see here, there used to exist an assumed healthy period between the two major phenotypes. We now know that a third phenotype exists that involves a failure to thrive and dyslipidemia.16

Neonatal intrahepatic cholestasiscaused by citrin defiency (NICCD)Children under the age of 1 year with NICCD have a transient intrahepatic cholestasis.Other findings include:Diffuse fatty liver with hepatomegaly and parenchymal cellular infiltration a/w hepatic fibrosisLow birth weightGrowth retardationHypoproteinemiaDecreased coagulation factorsHemolytic anemiaVariable (usually mild) liver dysfunctionHypoglycemia

Presents in the first few weeks of life with prolonged cholestasis/jaundice and metabolic abnormalities like aminoacidemia with elevated citrulline/tyrosine/threonine/arginine and/or methionine, galactosuria and increased alpha-fetoprotein.

Mechanism of fatty liver:Citrin deficiency causes a loss of the malate-aspartate shuttle and a compensatory up-regulation of the malate-citrate shuttle which results in an increased amount of citrate in the cytosol.This increase in citrate likely leads to an overproduction of fatty acids and enhanced uptake of fatty acids into the hepatocytes.17

Neonatal intrahepatic cholestasiscaused by citrin defiency (NICCD)Symptoms generally resolve by the time they are 1 year old with treatment, which includes fat-soluble vitamin supplementation and use of lactose-free formulas or formulas containing medium-chain triglycerides

Starting around the age of 1-2 years, children begin showing a strong preference for protein and lipid-rich foods and an aversion to sugar and carbohydrate-rich foods. NICCD blocks the flow of bile and prevents the body from processing certain nutrients properly. Ammonia does not build up in the blood so the signs and symptoms tend to resolve within one year.

Some of these children will later go on to develop severe CTLN2 (with neuropsychiatric symptoms) however this transition is typically very gradual.18

Failure to Thrive and Dyslipidemiacaused by Citrin Deficiency (FTTDCD)FTTDCD was recently proposed as a novel post-NICCD phenotype (before the onset of CTLN2) by Song et al in 2011.

Traditionally, it was assumed that there was an apparently healthy period after NICCD but before the onset of CTLN2.

DyslipidemiaAbnormal levels of triglyceride and cholesterol (including total, HDL, and LDL)

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Failure to Thrive and Dyslipidemiacaused by Citrin Deficiency (FTTDCD)In a citrin-deficient cohort of 51 children diagnosed in a Chinese pediatric center, they analyzed SLC25A13 mutations, identified dysmorphic erythrocytes, did hepatobiliary scintigraphic imaging and investigated the post-NICCD clinical presentations.

Twelve SLC25A13 mutations were detected, along with two novel mutations.

Among the 51 cases: 7 had echinocytosis which was a/w more severe biochemical abnormalities.9 demonstrated a failure to thrive and dyslipidemia, creating a phenotype that was different from either NICCD or CTLN2

20Failure to Thrive and Dyslipidemiacaused by Citrin Deficiency (FTTDCD)

In the 7 that were found to have it, the echinocytosis was transient and resolved in every case but one toddler with persistent echinocytosis that was eventually lethal due to cirrhosis. This might indicate that the presence of echinocytosis may be a marker of severe impairment in liver function and that a prolonged form may be a poor prognostic indicator in citrin deficiency.21

Citrullinemia Type II (CTLN2)Neuropsychiatric symptoms due to hyperammonemia that closely resemble those of other hepatic encephalopathy or urea cycle disorders:Nocturnal deliriumAberrant behaviors (aggression, irritability, and hyperactivity)DelusionsDisorientationRestlessnessDrowsinessLoss of memoryFlapping tremorConvulsive seizuresComa

Onset is usually between the ages of 20 and 50 years.

Also show a strong preference to protein and/or lipid-rich foods (like beans, peanuts, eggs, milk, cheese, fish and meat) and a strong aversion to carbohydrate-rich or sweet foods (like rice and juice).22

Citrullinemia Type II (CTLN2)Complications that occur in >10%:PancreatitisHyperlipidemiaFatty liverHepatoma

Biochemical findings for each type

Testing Strategy

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Order of testingPerform quantitative plasma amino acid analysis (children age 1-4 months).

Measure blood ammonia, plasma amino acids, PSTI, liver enzymes (when CTLN2 is suspected).

Perform dietary assessment, including food preferences

Perform molecular genetic testing:Sequence analysis of SLC25A13, followed by deletion/duplication analysis if neither or only one disease-causing mutation is identified.

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Mode of inheritance, Genotype-Phenotype Correlations and PenetranceAutosomal recessiveNo significant correlation exists between the SLC25A13 mutation types and a decreased level of hepatic enzyme ASS activity/protein or age of onset in individuals with CTLN2

For NICCD, the male-to-female ratio is roughly equal.For CTLN2, the male-to-female ratio is 2.4 to 1.The higher male-to-female ratio for CTLN2 suggests that for some unknown reason, homozygous females are more resistant to the CTLN2 phenotype than males.

For genetic counseling: Carrier testing for at-risk relatives and prenatal testing for pregnancies at increased risk are possible if the disease-causing mutations in the family are known.

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PrevalenceUntil recently, citrin deficiency was thought to be restricted to Japan; however, it is not recognized to be pan ethnic.

In Japan, the frequency of homozygotes or compound heterozygotes for SLC25A13 mutations is 1:17,000 based on a carrier or heterozygote rate of 1:65.

The observed prevalence of NICCD is 1:100,000 compared to that of CTLN2 which is 1:230,000.Because of this, it is believed that most homozygotes of Japanese heritage have NICCD.29

Treatment of ManifestationsNICCDsupplementation of fat-soluble vitamins and use of lactose-free formula (in those with galactosemia) or formulas containing medium-chain triglycerides31

Treatment of ManifestationsFTTDCDVery few treatment measures have been describedFed according to food preferences (high protein and lipid diet).Administration of sodium pyruvate may be effective in correcting growth retardation.

Although a low protein/high caloric diet helps prevent hyperammonemia in other forms of urea cycle enzyme deficiencies, it is harmful for individuals with all forms of citrin deficiency.because a high carb diet can increase NADH production which stimulates the citrate-malate shuttle leading to hyperammonemia, fatty liver and hypertriglyceridemia

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Treatment of ManifestationsCTLN2Most successful therapy has been liver transplantation.Administration of arginine has been reported to be effective in decreasing the blood ammonia concentration.

So whats Citrullinemia Type 1?Also has both an acute neonatal form and a milder late-onset form

However, the neonatal form is much more severe!

Hyperammonemia lethargic, poor feeding, vomiting ICP and deathAlso inherited in an autosomal recessive manner.34

So whats Citrullinemia Type 1?Deficiency of the enzyme arginosuccinate synthase (ASS) Plasma ammonia concentration can approach 3000 micromol/LPlasma quantitative amino acid analysis shows absence of arginosuccinic acid and concentration of citrulline >1000 micromol/L

So whats Citrullinemia Type 1?ASS1 is the only gene in which mutation is known to cause CTLN1

Treatment involves the Ucylyd protocol Sodium benzoate and phenylacetateMetabolically active compounds that serve as alternatives to urea for the excretion of waste nitrogen

Failure to control hyperammonia with the protocol after two doses requires hemodialysisAlong with this they must also have the appropriate diet36

Neonatal screeningCitrin deficiency is detectable by tandem mass spectrometry (MS/MS)

California and other states screen for citrin deficiency

Texas only screens for Type 1 Citrullinemia

Who does gene testing?3 labs can perform sequence analysis of the coding region however none are located in the US

Several labs (including Baylor) offer supplemental newborn screening and amino acid analysis

New research!New research has shown that the SLC gene has a very rich transcript diversity and that cDNA cloning may be a useful tool in the diagnosis of citrin deficiency.

ReferencesMichiharu Komatsu, et al. Citrin deficiency as a cause of chronic liver disorder mimicking non-alcoholic fatty liver disease, Journal of Hepatology, Volume 49, Issue 5, November 2008, Pages 810-820. (http://www.sciencedirect.com/science/article/pii/S0168827808003553) Kobayashi K, Saheki T, Song YZ. Citrin Deficiency. 2005 Sep 16 [Updated 2012 Jan 5]. In: Pagon RA, Bird TD, Dolan CR, et al., editors. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; 1993-. Available from: http://www.ncbi.nlm.nih.gov/books/NBK1181/Song YZ, et al. Genotypic and phenotypic features of citrin deficiency: Five-year experience in a Chinese pediatric center. Int J Mol Med. 2011;28:3340. Zhan-Hui Zhang, et al. Molecular analysis of SLC25A13 gene in human peripheral blood lymphocytes: Marked transcript diversity, and the feasibility of cDNA cloning as a diagnostic tool for citrin deficiency, Gene, Volume 511, Issue 2, 15 December 2012, Pages 227-234. (http://www.sciencedirect.com/science/article/pii/S0378111912011444)

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