Multiple carboxylase deficiency, late onset

Multiple Carboxylase Deficiency, Late Onset (MCDLO) is a rare metabolic disorder characterized by a deficiency in the activity of the enzymes involved in the biotin-dependent carboxylation reactions. These enzymes play a crucial role in various metabolic pathways, including the metabolism of fats, proteins, and carbohydrates. MCDLO is a form of Multiple Carboxylase Deficiency (MCD), which is divided into early and late-onset forms, with the late-onset form typically presenting in late childhood or adulthood.

Symptoms and Signs

The symptoms of MCDLO can vary widely among individuals but often include skin rash, hair loss (alopecia), seizures, ataxia (lack of muscle coordination), developmental delay, and immune system impairments. Metabolic acidosis, characterized by an excessive acid buildup in the body, is also a common feature.

Causes

MCDLO is caused by mutations in the HLCS gene, which encodes the enzyme holocarboxylase synthetase. This enzyme is responsible for attaching biotin to carboxylase enzymes, a process essential for their activation. Mutations in the HLCS gene lead to reduced activity of multiple carboxylase enzymes, disrupting normal metabolic processes.

Diagnosis

Diagnosis of MCDLO involves a combination of clinical evaluation, biochemical tests, and genetic testing. Biochemical tests may reveal elevated levels of specific organic acids in the urine and abnormal levels of certain amino acids in the blood. Genetic testing can confirm a diagnosis by identifying mutations in the HLCS gene.

Treatment

The primary treatment for MCDLO is lifelong supplementation with biotin, a vitamin that acts as a coenzyme for the carboxylase enzymes. High doses of biotin can restore the activity of these enzymes and alleviate symptoms in many patients. Regular monitoring and supportive care for complications such as seizures or immune system deficiencies may also be necessary.

Prognosis

With early diagnosis and treatment, individuals with MCDLO can often lead normal, healthy lives. However, the prognosis can vary depending on the severity of the enzyme deficiency, the age at diagnosis, and the response to biotin therapy.

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