Functional and molecular studies in primary carnitine deficiency.

Area of Science:

• Genetics
• Biochemistry
• Metabolic Disorders

Background:

• Primary carnitine deficiency results from OCTN2 transporter defects (SLC22A5 gene).
• This condition can lead to severe health issues like hypoglycemia, cardiomyopathy, and sudden death.
• Reduced carnitine transport in patient fibroblasts is a key diagnostic indicator.

Purpose of the Study:

• To evaluate carnitine transport in fibroblasts from individuals suspected of having primary carnitine deficiency.
• To identify causative variants in the SLC22A5 gene and assess their functional impact.
• To determine the diagnostic utility of genetic sequencing versus functional studies for primary carnitine deficiency.

Main Methods:

• Assessed carnitine transport in fibroblasts from 358 subjects.
• Sequenced the SLC22A5 gene in 95 subjects with reduced carnitine transport.
• Expressed identified missense variants in CHO cells to evaluate functional impact.
• Utilized prediction algorithms (Polyphen-2, SIFT) to assess variant effects.

Main Results:

• Reduced carnitine transport (<20% of normal) was observed in 140 out of 358 subjects.
• Causative SLC22A5 variants were found in 84% of alleles analyzed.
• Functional studies confirmed impaired transport for 73 out of 92 expressed variants.
• Prediction algorithms accurately predicted variant effects in approximately 80% of cases.

Conclusions:

• Genetic mutations in the coding region of SLC22A5 are not identified in all cases of primary carnitine deficiency.
• Prediction algorithms have limitations in assessing the functional impact of variants in transmembrane proteins.
• Functional studies using patient fibroblasts remain essential for accurate diagnosis of primary carnitine deficiency.