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

Secondary acrodermatitis enteropathica-like skin findings in a case of methylmalonic acidemia

Methylmalonic acidemia (MMA) is an autosomal recessive genetic disorder caused by decreased activity of methylmalonyl-CoA mutase or metabolic disturbance of its coenzyme cobalamin, cutaneous manifestations are rare clinical signs in this disease. Herein, we describe a Chinese boy with MMA fed with a formula lacking branched-chain amino acids presenting with erythroderma and acrodermatitis enteropathica-like rash, a homozygous nonsense mutation c.742C>T (p.Gln248*) was identified in the MMAA gene. The pedigree exhibited a non-Mendelian inheritance pattern which was attributed to maternal uniparental disomy on chromosome 4q26-q34.1 of the proband, confirmed by chromosomal microarray analysis. Our case highlights the association between skin changes and nutritional deficiency due to therapeutic amino acid restrictions in MMA.

A Novel Genetic Variant in the WFS1 Gene in a Patient with Partial Uniparental Mero-Isodisomy of Chromosome 4

Wolfram syndrome is a rare autosomal recessive disorder characterized by optic atrophy and diabetes mellitus. Wolfram syndrome type 1 (WFS1) is caused by bi-allelic pathogenic variations in the wolframin gene. We described the first case of WFS1 due to a maternal inherited mutation with uniparental mero-isodisomy of chromosome 4. Diabetes mellitus was diagnosed at 11 years of age, with negative anti-beta cells antibodies. Blood glucose control was optimal with low insulin requirement. No pathogenic variations in the most frequent gene causative of maturity-onset diabetes of the young subtypes were detected. At 17.8 years old, a rapid reduction in visual acuity occurred. Genetic testing revealed the novel homozygous variant c.1369A>G; p.Arg457Gly in the exon 8 of wolframin gene. It was detected in a heterozygous state only in the mother while the father showed a wild type sequence. In silico disease causing predictions performed by Polyphen2 classified it as “likely damaging”, while Mutation Tester and Sift suggested it was “polymorphism” and “tolerated”, respectively. High resolution SNP-array analysis was suggestive of segmental uniparental disomy on chromosome 4. In conclusion, to the best of our knowledge, we describe the first patient with partial uniparental mero-isodisomy of chromosome 4 carrying a novel mutation in the wolframin gene. The clinical phenotype observed in the patient and the analysis performed suggest that the genetic variant detected is pathogenetic.

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

BACKGROUND

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

METHODS

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

RESULTS

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.

CONCLUSION

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.