Clinical and Basic Investigations of Methylmalonic Acidemia (MMA) and Related Disorders
Methylmalonic acidemia (MMA), one of the most common inborn errors of organic acid metabolism, is heterogeneous in etiology and clinical manifestations. Affected patients with cblA, cblB and mut classes of MMA are medically fragile and can suffer from complications such as metabolic stroke or infarction of the basal ganglia, pancreatitis, end stage renal failure, growth impairment, osteoporosis, and developmental delay. The frequency of these complications and their precipitants remain undefined. Furthermore, current treatment protocol outcomes have continued to demonstrate substantial morbidity and mortality in the patient population. Increasingly, solid organ transplantation (liver, and/or kidney) has been used to treat patients. Disordered transport and intracellular metabolism of vitamin B12 produces a distinct group of disorders that feature methylmalonic acidemia as well as (hyper)homocysteinemia. These conditions are named after the corresponding cellular complementation class - (cblC, cblD, cblF, cblJ and cblX) - and are also heterogenous, clinically and biochemically. The genetic disorders underlying cblE and cblG feature an isolated impairment of the activity of methionine synthase, a critical enzyme involved in the conversion of homocysteine to methionine and these disorders feature (hyper) homocysteinemia. Lastly, a group of patients can have increased methylmalonic acid and/or homocysteine in the blood or urine caused by variant(s) in recently identified (ACSF3) and unknown genes. In this protocol, we will clinically evaluate patients with methylmalonic acidemia and cobalamin metabolic defects. Routine inpatient admissions will last up to 4-5 days and involve urine collection, blood drawing, ophthalmological examination, radiological procedures, MRI/MRS, skin biopsies in some, and developmental testing. In a subset of patients who have or will receive renal, hepato- or hepato-renal transplants or have an unusual variant or clinical course and have MMA, a lumbar puncture to examine CSF metabolites will be performed. In this small group of patients, CSF metabolite monitoring may be used to adjust therapy. The study objectives will be to further delineate the spectrum of phenotypes and characterize the natural history of these enzymopathies, query for genotype/enzymatic/phenotype correlations, search for new genetic causes of methylmalonic acidemia and/or homocysteinemia, identify new disease biomarkers and define clinical outcome parameters for future clinical trials. The population will consist of participants previously evaluated at NIH, physician referrals, and families directed to the study from clinicaltrials.gov as well as the Organic Acidemia Association, Homocystinuria Network America and other national and international support groups. Most participants will be evaluated only at the NIH Clinical Center. However, if the NIH team decides that a patient under the age of 2 years is a candidate subject for this research protocol, that patient may enroll at the Children's National Medical Center (CNMC) site, pending approval by Dr Chapman, the Principal Investigator of the CNMC location Individuals may also enroll in the tissue collection only part of the study at the UPMC Children's Hospital of Pittsburgh or share medical history and clinical data via telemedicine visits remotely. Outcome measures will largely be descriptive and encompass correlations between clinical, biochemical and molecular parameters.
• Patients of any sex, ethnicity, and over 1 month of age with biochemical or genetic diagnosis of methylmalonic acidemia or cobalamin disorders are eligible to enroll in this protocol. The primary reason for expanding enrollment to young children is because individuals with cobalamin C deficiency (cblC) develop a maculopathy often in utero or early infancy yet the natural history of the disease progression in these early years has not been well defined. Our colleagues at the National Eye Institute have documented the retinal findings in the largest cohort of individuals with cblC and have developed an expertise in this disorder. A recent report suggests that early treatment may significantly improve the retinal disease and will be the focus of a future clinical trial at the NIH Clinical Center requiring a need for more natural history data from birth to early childhood. Children ages 1 month to 2 years or under 12 kg will be reviewed by the Pediatric Consult Service prior to scheduling and if approved will be evaluated in the outpatient clinic for limited evaluations blood draw, eye exam, consults. Affected infants that are not approved by the Pediatric Consult Service or are not stable enough to travel may enroll remotely by telemedicine to include in natural history data collection, such as medical history and laboratory result sharing and interpretation, molecular genetic testing, genetic counseling, nutrition consult with dietary food log analysis, neurocognitive assessments. Affected individuals of any of the other disorders under study, younger than 2 years may be evaluated at Children s National Medical Center (CNMC) as part of an evolving agreement in the Translational Program in Pediatrics, if they are deemed eligible for participation by the NIH team and the CNMC team. Patients will be diagnosed based on a determination of MMA and homocysteine levels in plasma and urine. Most will have their complementation class known or pending. Molecular genetic analyses to determine mutations will be expected to have been performed prior to acceptance into the study. Some patients who have not yet had these laboratory tests will be admitted to the protocol based upon metabolic parameters and clinical history. This latter category of patients might include individuals with a suspected genetic but unknown type of MMA.