Carnitine palmitoyltransferase II deficiency: a clinical, biochemical, and molecular review

Congenital deficiency of carnitine palmitoyltransferase (CPT) II has been known for at least 30 years now, and its phenotypic variability remains fascinating. Three distinct clinical entities have been described, the adult, the infantile, and the perinatal, all with an autosomal recessive inheritance pattern. The adult CPT II clinical phenotype is somewhat benign and requires additional external triggers such as high-intensity exercise before the predominantly myopathic symptoms are elicited. The perinatal and infantile forms involve multiple organ systems. The perinatal disease is the most severe form and is invariably fatal. The introduction of mass spectrometry to analyze blood acylcarnitine profiles has revolutionized the diagnosis of fatty acid oxidation disorders including CPT II deficiency. Its use in expanded neonatal screening programs has made presymptomatic diagnosis a reality. An increasing number of mutations are being identified in the CPT II gene with a distinct genotype-phenotype correlation in most cases. However, clinical variability in some patients suggests additional genetic or environmental modifiers. Herein, we present a new case of lethal perinatal CPT II deficiency with a rare missense mutation, R296Q (907G>A) associated with a previously described 25-bp deletion on the second allele. We review the clinical features, the diagnostic protocol including expanded neonatal screening, the treatment, and the biochemical and molecular basis of CPT II deficiency.

Biological sample collection and processing for molecular epidemiological studies

Molecular epidemiology uses biomarkers and advanced technology to refine the investigation of the relationship between environmental exposures and diseases in humans. It requires careful handling and storage of precious biological samples with the goals of obtaining a large amount of information from limited samples, and minimizing future research costs by use of banked samples. Many factors, such as tissue type, time of collection, containers used, preservatives and other additives, transport means and length of transit time, affect the quality of the samples and the stability of biomarkers and must be considered at the initial collection stage. An efficient study design includes provisions for further processing of the original samples, such as cryopreservation of isolated cells, purification of DNA and RNA, and preparation of specimens for cytogenetic, immunological and biochemical analyses. Given the multiple uses of the samples in molecular epidemiology studies, appropriate informed consent must be obtained from the study subjects prior to sample collection. Use of barcoding and electronic databases allow more efficient management of large sample banks. Development of standard operating procedures and quality control plans is a safeguard of the samples' quality and of the validity of the analyses results. Finally, specific state, federal and international regulations are in place regarding research with human samples, governing areas including custody, safety of handling, and transport of human samples, as well as communication of study results.Here, we focus on the factors affecting the quality and the potential future use of biological samples and some of the provisions that must be made during collection, processing, and storage of samples, based on our experience in the Superfund Basic Research Program and Children's Environmental Health Center, at the University of California, Berkeley.

Lethal neonatal and severe late infantile forms of carnitine palmitoyltransferase II deficiency associated with compound heterozygosity for different protein truncation mutations

We describe a lethal neonatal form of carnitine palmitoyltransferase II (CPT II) deficiency with compound heterozygosity for 2 truncation mutations (Q413fs and 109AGC --> GCAGC). A new phenotype for a severe late infantile form of CPT II deficiency with hypoglycemia is associated with compound heterozygosity for the severe Q413fs mutation and a mild point mutation (P50H).

Phenotypic variability among first-degree relatives with carnitine palmitoyltransferase II deficiency

Carnitine palmitoyltransferase (CPT) II deficiency disorders are clinically very variable. To examine the cause(s) of variable symptoms in first-degree relatives with CPT II deficiency, four sisters with various combinations of mutations and polymorphisms in the CPT2 gene were studied, together with 20 sedentary and 24 trained healthy female subjects. One sister, whose symptoms began at age 7 years, was more severely affected than her older sister, whose symptoms began at age 16 years; both were compound heterozygotes for the common S113L mutation and Q413fs, and for the common CPT2 polymorphisms, V3681 and M647V. A third sister became hypoglycemic with fasting, was heterozygous for the S113L mutation, and homozygous for the polymorphism variants. The fourth sister was asymptomatic, heterozygous for the Q413fs mutation, and homozygous for the normal polymorphisms. Residual CPT II activity in skeletal muscle and cultured skin fibroblasts from the two myopathic sisters, and palmitate oxidation in fibrobasts, were abnormally low; cellular and total body fat oxidation were also diminished. Muscle function and fat oxidation were nomal at rest, but a switch to carbohydrate utilization occurred at lower exercise intensities than in sedentary and trained individuals, respectively. Reliance on carbohydrates during stress and hormonal alterations may explain, in part, the variance in ages of onset and serverity of symptoms in myopathic patients.

Screening for carnitine palmitoyltransferase II deficiency by tandem mass spectrometry

Mitochondrial carnitine palmitoyltransferase II (CPT II) deficiency is the most common inherited disorder of lipid metabolism in adults. Currently the routine diagnosis is based on the determination of CPT enzyme activity in muscle tissue. We have analysed the tandem mass spectra of serum acylcarnitines of nine CPT II-deficient patients. These spectra were compared to those of a cohort of 99 patients with other neuromuscular disorders and metabolic conditions supposed to cause alterations of the long-chain acylcarnitines. The spectra in CPT II deficiency showed characteristic elevations of C16:0 and C18:1 acylcarnitines while acetylcarnitine C2 was not elevated. In the present study, the ratio (C16:0+C18:1)/C2 has detected all CPT II deficiencies and discriminated them from unspecific alterations of serum acylcarnitines. The ratios of CPT II-deficient patients showed virtually no overlap with those observed in patients with other neuromuscular disorders. We suggest mass spectrometry of serum acylcarnitines as a rapid screening test that should be included early in the diagnostic work-up of patients with recurrent myoglobinuria, recurrent muscular weakness and myalgia.

A variable myopathy associated with heterozygosity for the R503C mutation in the carnitine palmitoyltransferase II gene

Adult-onset carnitine palmitoyltransferase II (CPT II) deficiency is an autosomal recessive disease characterized by muscle pain and stiffness with rhabdomyolysis and myoglobinuria in severe cases. Exercise, fasting, viral infection, anesthesia, or extremes in temperature may trigger symptoms. A 54-year-old woman exhibited a 35-year history of progressive weakness and myopathic symptoms. CPT II activity in the patient's lymphoblasts, cultured skin fibroblasts, and skeletal muscle was reduced to 47, 43, and 13% of normal, respectively. Respiratory chain enzymes were also reduced in muscle ranging from 22 to 49% of their respective normal reference means. beta-oxidation enzymes in fibroblasts ranged from 29 to 63% of normal. The patient, her father, and her 26-year-old son were all heterozygous for the R503C mutation. The patient's son has a lifelong history of myopathic symptoms while his grandfather only had mild weakness during childhood. Analysis of the V368I and M647V polymorphisms in the CPT2 gene showed that the mutant allele is linked to 368I and 647M in this family and that the normal allele is linked to 647V in the affected patient and her son, and to 647M in the patient's father. While the variability in CPT2 gene haplotypes may contribute to the phenotypic complexities in this family, it is also possible that an additional gene defect in the transport of mitochondrial proteins contributes to the complex phenotype in the patient. We present biochemical and molecular evidence for vertical transmission of a variable myopathy caused by heterozygosity for a single mutation, R503C, in the CPT2 gene.