Molecular basis of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: identification of two new mutations

Acute Fatty Liver of Pregnancy

Acute fatty liver of pregnancy (AFLP) is a rare but life-threatening condition that develops in the third trimester of pregnancy. AFLP shares similar clinical features with other more common pregnancy-associated conditions. However, early correct diagnosis is important for maternal and fetal survival. Once the diagnosis has been established, immediate delivery and maternal intensive support should be undertaken. Both parents and the infant should be tested for deficiencies of the mitochondrial fatty acid oxidation, especially for long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency, as many cases of AFLP are related to disruption of this physiological enzymatic pathway.

Diagnosis, Treatment, and Clinical Outcome of Patients with Mitochondrial Trifunctional Protein/Long-Chain 3-Hydroxy Acyl-CoA Dehydrogenase Deficiency

Deficiency of the mitochondrial trifunctional protein (TFP) and long-chain 3-Hydroxy Acyl-CoA dehydrogenase (LCHAD) impairs long-chain fatty acid oxidation and presents with hypoglycemia, cardiac, liver, eye, and muscle involvement. Without treatment, both conditions can be life-threatening. These diseases are identified by newborn screening (NBS), but the impact of early treatment on long-term clinical outcome is unknown. Moreover, there is lack of consensus on treatment, particularly on the use of carnitine supplementation. Here, we report clinical and biochemical data in five patients with TFP/LCHAD deficiency, three of whom were diagnosed by newborn screening. All patients had signs and symptoms related to their metabolic disorder, including hypoglycemia, elevated creatine kinase (CK), and rhabdomyolysis, and experienced episodes of metabolic decompensation triggered by illness. Treatment was started shortly after diagnosis in all patients and consisted of a diet low in long-chain fats supplemented with medium chain triglycerides (MCT), essential fatty acids, and low-dose carnitine (25 mg/kg/day). Patients had growth restriction early in life that resolved after 2 years of age. All patients but the youngest (2 years old) developed pigmentary retinopathy. Long-chain hydroxylated acylcarnitines did not change significantly with age, but increased during acute illnesses. Free carnitine levels were maintained within the normal range and did not correlate with long-chain hydroxylated acylcarnitines. These results show that patients with LCHAD deficiency can have normal growth and development with appropriate treatment. Low-dose carnitine supplements prevented carnitine deficiency and did not result in increased long-chain hydroxylated acylcarnitines or any specific toxicity.

Comprehensive cDNA study and quantitative analysis of mutant HADHA and HADHB transcripts in a French cohort of 52 patients with mitochondrial trifunctional protein deficiency

BACKGROUND

Deficiency of mitochondrial trifunctional protein (MTP) is caused by mutations in the HADHA and HADHB genes, which have been mostly delineated at the genomic DNA level and have not been always elucidated.

AIM

To identify mutations in a French cohort of 52 MTP deficient patients and the susceptibility of mutations generating premature termination codons (PTCs) to the nonsense mRNA mediated decay (NMD).

METHODS

Mutation screening in fibroblasts was performed at the cDNA level and real-time RT-PCR was used to compare the levels of the different PTC-bearing mRNAs before and after a treatment of fibroblasts by emetine, a translation inhibitor.

RESULTS

A mutation detection rate of 100% was achieved. A total of 22 novel mutations were identified, including a large-sized genomic deletion in HADHB gene. A high proportion of all identified mutations were non-sense, frameshift and splicing mutations, generating (PTCs), distributed essentially on HADHA coding regions. We could demonstrate that the majority of mutations resulting in PTCs conform to the established rules governing the susceptibility to NMD.

CONCLUSION

Our results emphasize the value of cDNA analysis in the characterization of HADHA and HADHB mutations and further strengthen the model of haploinsufficiency as a major pathomechanism in MTP defects.

Study of deep intronic sequence exonization in a Japanese neonate with a mitochondrial trifunctional protein deficiency

Mitochondrial trifunctional protein (MTP) comprises heterooctamer alpha4beta4 and a deficiency in this protein causes a mitochondrial long-chain beta-oxidation defect. Here, we describe the molecular basis of an MTPbeta-subunit deficiency in a Japanese neonate. Mutation screening at the genomic level including all exons and exon-intron boundaries identified a novel c.1136A>G (H346R) mutation in exon 13 of the maternal allele, but none in the paternal allele. Analysis by RT-PCR identified paternal-specific 106- and 56-bp intronic insertions between exons 7 and 8, which introduced premature terminations. This intronic exonization was caused by a deep intronic mutation in intron 7 on the paternal allele that generates a cryptic splice donor site. This is the first report of a deep intronic mutation in MTP deficiency.

Acute fatty liver of pregnancy

Acute fatty liver of pregnancy (AFLP) is a rare, potentially fatal complication that occurs in the third trimester or early postpartum period. Although the exact pathogenesis is unknown, this disease has been linked to an abnormality in fetal fatty acid metabolism. Early diagnosis of AFLP sometimes can be difficult because it shares features with other common conditions such as pre-eclampsia, viral hepatitis and cholestasis of pregnancy. However, a careful history and physical examination, in conjunction with compatible laboratory and imaging results, are often sufficient to make the diagnosis, and liver biopsy is rarely indicated. Supportive care and expeditious delivery are essential to optimal maternal-fetal outcomes and remain as the mainstay treatment for AFLP.

Liver disease in pregnancy

Liver dysfunction during pregnancy can be caused by conditions that are specific to pregnancy or by liver diseases that are not related to pregnancy itself. This review attempts to summarize the epidemiology, pathophysiology, and management of the different pregnancy-related liver diseases, and to review different liver diseases not related to pregnancy and how they may affect or be effected by pregnancy. Some of the liver diseases specific to pregnancy can cause significant morbidity and mortality both to the mother and to the fetus, while most of the liver diseases not specific to pregnancy do not have a deleterious effect on the pregnancy itself.