A JAPANESE ADULT FORM OF CPT II DEFICIENCY ASSOCIATED WITH A HOMOZYGOUS F383Y MUTATION

Carnitine palmitoyltransferase II deficiency with a focus on newborn screening

Carnitine palmitoyltransferase (CPT) II deficiency is one of the most common forms of mitochondrial fatty acid oxidation disorder. Its clinical phenotypes are classified into the muscle, severe infantile, and lethal neonatal forms. Among Caucasians, the muscle form predominates, and the c.338C > T (p.S113L) variant is detected in most cases, whereas among the Japanese, c.1148T > A (p.F383Y) is the variant allele occurring with the highest frequency and can apparently cause symptoms of the severe infantile form. Newborn screening (NBS) for this potentially fatal disease has not been established. We encountered an infantile case of CPT II deficiency not detected in NBS using C16 and C18:1 concentrations as indices, and therefore we adopted the (C16 + C18:1)/C2 ratio as an alternative primary index. As a result, the disease was diagnosed in nine of 31 NBS-positive subjects. The values for (C16 + C18:1)/C2 in the affected newborns partly overlapped with those in unaffected ones. Among several other indices proposed previously, C14/C3 has emerged as a more promising index. Based on these findings, nationwide NBS for CPT II deficiency using both (C16 + C18:1)/C2 and C14/C3 as indices was officially approved and started in April 2018. We diagnosed the disease in four young children presenting with symptoms of the muscle form, whose values for the new indices were not elevated. Although it is still difficult to detect all cases of the muscle form of CPT II deficiency in NBS, our system is expected to save many affected children in Japan with the severe infantile form predominating.

A newborn case with carnitine palmitoyltransferase II deficiency initially judged as unaffected by acylcarnitine analysis soon after birth

Carnitine palmitoyltransferase II (CPT-2) deficiency, an autosomal recessive disorder of fatty acid oxidation, can be detected by newborn screening using tandem mass spectrometry (TMS).

Our case was a boy born at 38 weeks and 6 days of gestation via normal vaginal delivery; his elder sister was affected with CPT-2 deficiency. Acylcarnitine (AC) was analyzed in both dried blood spots (DBS) and serum 2 h after birth to determine whether the boy was also affected. His C16 and C18:1 AC levels in DBS were in the normal range, while his serum long-chain AC levels were marginally increased but lower than those of his sister. After the samples were taken, he was treated with glucose infusion to prevent any catabolism for 2 days. On day 4, the long-chain AC levels in both DBS and serum obtained were higher than those on day 0 and were equivalent to those of his sister. Genetic testing confirmed the presence of the same mutation found in his sister, a homozygous F383Y mutation in the CPT2 gene, thus leading to the diagnosis of CPT-2 deficiency.

The sample for TMS should be taken between days 1 and 7. If the sample is not obtained at an appropriate time, correct diagnosis may not be made, as in our case. Although early diagnosis is required, samples taken within 24 h after birth should not be used for TMS.

Metabolic autopsy with next generation sequencing in sudden unexpected death in infancy: Postmortem diagnosis of fatty acid oxidation disorders

The recent introduction of metabolic autopsy in the field of forensic science has made it possible to detect hidden inherited metabolic diseases. Since the next generation sequencing (NGS) has recently become available for use in postmortem examinations, we used NGS to perform metabolic autopsy in 15 sudden unexpected death in infancy cases. Diagnostic results revealed a case of carnitine palmitoyltransferase II deficiency and some cases of fatty acid oxidation-related gene variants. Metabolic autopsy performed with NGS is a useful method, especially when postmortem biochemical testing is not available.

•

This is the first metabolic autopsy performed with next generation sequencing (NGS).

•

We detected one case of CPT II deficiency and three cases of FAOD-related rare variants.

•

Some of them had no specific abnormality except for genetic variants.

•

These cases would be undetected without NGS.

•

We advocate metabolic autopsy performed with NGS.

Association of CPT II gene with risk of acute encephalitis in Chinese children

BACKGROUND

Mutations of the CPT II gene cause CPT II deficiency, an inborn metabolic error affecting mitochondrial fatty acid β-oxidation. Associations and mechanisms of CPT II gene with acute encephalitis need to be elucidated. We aimed to investigate the associations of CPT II gene variants and CPT II activity with development of acute encephalitis.

METHODS

A total of 440 blood-unrelated Chinese children with acute encephalitis and 229 healthy controls were enrolled in this case control study. Sequencing of 5 exons of the CPT II gene was carried out to look for the variants associated with acute encephalitis. CPT II activity and blood adenosine triphosphate concentration were examined during high fever and convalescent phase to confirm the hypothesis.

RESULTS

Polymorphism of rs2229291 in CPT II gene was significantly associated with an increased risk of acute encephalitis (P = 0.031), where as rs1799821 displayed a decrease risk (P = 0.018). Positive association was found between rs2229291 and patients with fever at onset of seizure and degree of pathogenetic condition (P = 0.018 and P = 0.023), but not for rs1799821. CPT II activity of patients with rs2229291 reduced greatly during high fever compared with the convalescent phase.

CONCLUSIONS

rs2229291 and rs1799821 variants in CPT II gene might be 1 of the predisposing factors of acute encephalitis.

Three novel mutations in the carnitine-acylcarnitine translocase (CACT) gene in patients with CACT deficiency and in healthy individuals

Carnitine-acylcarnitine translocase (CACT) and carnitine palmitoyltransferase II (CPT2) are key enzymes for transporting long-chain fatty acids into mitochondria. Deficiencies of these enzymes, which are clinically characterized by life-threatening non-ketotic hypoglycemia and rhabdomyolysis, cannot be distinguished by acylcarnitine analysis performed using tandem mass spectrometry. We had previously reported the CPT2 genetic structure and its role in CPT2 deficiency. Here, we analyzed the CACT gene in 2 patients diagnosed clinically with CACT deficiency, 18 patients with non-traumatic rhabdomyolysis and 58 healthy individuals, all of whom were confirmed to have normal CPT2 genotypes. To facilitate CACT genotyping, we used heat-denaturing high-performance liquid chromatography (DHPLC), which helped identify five distinct patterns. The abnormal heteroduplex fragments were subjected to CACT-specific DNA sequencing. We found that one patient with CACT deficiency, Case 1, carried c.576G>A and c.199-10t>g mutations, whereas Case 2 was heterozygous for c.106-2a>t and c.576G>A. We also found that one patient with non-traumatic rhabdomyolysis and one healthy individual were heterozygous for c.804delG and the synonymous mutation c.516T>C, respectively. In summary, c.576G>A, c.106-2a>t and c.516T>C are novel CACT gene mutations. Among the five mutations identified, three were responsible for CACT deficiency. We have also demonstrated the successful screening of CACT mutations by DHPLC.

Retrospective review of Japanese sudden unexpected death in infancy: the importance of metabolic autopsy and expanded newborn screening

Sudden unexpected death in infancy is defined as sudden unexpected death occurring before 12 months of age. The common causes of sudden unexpected death in infancy are infection, cardiovascular anomaly, child abuse, and metabolic disorders. However, the many potential inherited metabolic disorders are difficult to diagnose at autopsy and may therefore be underdiagnosed as a cause of sudden unexpected death in infancy. In the present study we retrospectively reviewed 30 Japanese sudden unexpected death in infancy cases encountered between 2006 and 2009 at our institute. With postmortem blood acylcarnitine analysis and histological examination of the liver, we found two cases of long-chain fatty acid oxidation defects. Molecular analysis revealed that the one patient had a compound heterozygote for a novel mutation (p.L644S) and a disease-causing mutation (p.F383Y) in the carnitine palmitoyltransferase 2 gene. Furthermore, retrospective acylcarnitine analysis of the newborn screening card of this patient was consistent with carnitine palmitoyltransferase II deficiency. Metabolic autopsy and expanded newborn screening would be helpful for forensic scientists and pediatricians to diagnose fatty acid oxidation disorders and prevent sudden unexpected death in infancy.

Mutations of carnitine palmitoyltransferase II (CPT II) in Japanese patients with CPT II deficiency

Carnitine palmitoyltransferase II (CPT II) deficiency is an inherited disorder involving beta-oxidation of long-chain fatty acids. CPT II deficiency is a wide-spectrum disorder that includes a lethal neonatal form, an infantile form, and an adult-onset form. However, the ethnic characteristics and the relationship between genotype and clinical manifestation are not well understood. We investigated three non-consanguineous Japanese patients with CPT II deficiency and examined cell lines from 4 unrelated patients and 50 healthy donors. The CPT 2 gene was typed by direct DNA sequencing of polymerase chain reaction-amplified gene products. Case 1 (infantile form) was heterozygous for a phenylalanine to tyrosine substitution at position 383 (p.F383Y) and a novel valine to leucine substitution at 605 (p.V605L). Cases 2, 4, and 5 (infantile form) and case 3 (adult-onset form) were heterozygous for a single mutation at F383Y. Case 6 (adult-onset form) was compound heterozygous at the CPT 2 locus, with deletion of cytosine and thymine at residue 408, resulting in a stop signal at 420 (p.Y408fsX420), and an arginine to cysteine substitution at position 631 (p.R631C). Case 7 (adult-onset form) was homozygous for the p.F383Y mutation. In conclusion, we identified p.F383Y mutations in six of seven patients with CPT II deficiency and two novel variants of the coding gene: p.Y408fsX420 and p.V605L. These mutations differ from those in Caucasian patients, who commonly harbor p.S113L, p.P50H, and p.Q413fsX449 mutations; therefore, our data and those of other Japanese groups suggest that the p.F383Y mutation is significant in Japanese patients with CPT II deficiency.