Segmental uniparental disomy of chromosome 4 in a patient with methylmalonic acidemia

Methylmalonic acidemia (MMA) is an autosomal recessive genetic disorder involving the metabolism of organic acids.

Here, we report the case of a patient who developed acute metabolic crisis after vaccination and was diagnosed with cblA type MMA after hospitalization.

Further examination revealed a homozygous pathogenic variant in the MMAA gene that caused the disease in the patient but did not conform to Mendelian inheritance. Using chromosomal microarray analysis, maternal uniparental disomy (UPD) was found on chromosome 4q26-q35.2 of the patient. The MMAA gene of the patient was inherited only from the mother and carried the same pathogenic variant on both alleles of chromosome 4. MMAA gene expression levels in whole blood were detected by real-time PCR.

The nonsense pathogenic variant, NM_172250.2:c.742C>T (p.Gln248*), carried by the patient leads to a premature termination of transcription of the gene, thereby resulting in partial loss of protein function while retaining some others. Segmental UPD 4 is rare, and to our knowledge, has not been reported previously.