CaseWG2098: 3 yrs onset

CasePresentingHPOs: HP:0001251, HP:0004302, HP:0001260, HP:0002313, HP:0012120 (Ataxia, Functional motor deficit, Dysarthria, Spastic paraparesis, Methylmalonic aciduria)

HPOsFreeText: N/A

CaseNotHPOs: N/A

NotHPOsFreeText: N/A

CaseAddInfo: Proband has normal 14C-propionate incorporation, suggesting normal MCEE protein activity level; The high gnomAD frequency and homozygotes suggests this is likely a benign polymorphism

CasePreviousTesting: Normal MRI; Propionate Incorporation w/o hydroxycobalamin at 7.0 nmols/mg protein/18hr; Propionate Incorporation with hydroxycobalamin at 8.2 nmols/mg protein/18hr; Adenosylcobalamin synthesis percentage at 12.7%; Elevated methylmalonic values of 621 µmol/mmol creatinine (reference 0.8-5.2 µmol/mmol creatinine)

CaseGenotypingMethod: Genomic DNA was extracted from patient fibroblasts, sequenced, and the three MCEE/thirteen MUT exons were analyzed and amplified. Any reported mutations were resequenced from fresh PCR product.

Variant: NM_032601.4(MCEE):c.178A>C (p.Lys60Gln)

ClinVar: 203812, https://www.ncbi.nlm.nih.gov/clinvar/variation/203812/

gnomAD: 0.01463 (10 homozygotes), https://gnomad.broadinstitute.org/variant/2-71351536-T-G

CaseWG2098: 3 yrs onset

CasePresentingHPOs: HP:0001251, HP:0004302, HP:0001260, HP:0002313, HP:0012120 (Ataxia, Functional motor deficit, Dysarthria, Spastic paraparesis, Methylmalonic aciduria)

HPOsFreeText: N/A

CaseNotHPOs: N/A

NotHPOsFreeText: N/A

CaseAddInfo: Proband has normal 14C-propionate incorporation, suggesting normal MCEE protein activity level; The high gnomAD frequency and homozygotes suggests this is likely a benign polymorphism

CasePreviousTesting: Normal MRI; Propionate Incorporation w/o hydroxycobalamin at 7.0 nmols/mg protein/18hr; Propionate Incorporation with hydroxycobalamin at 8.2 nmols/mg protein/18hr; Adenosylcobalamin synthesis percentage at 12.7%; Elevated methylmalonic values of 621 µmol/mmol creatinine (reference 0.8-5.2 µmol/mmol creatinine)

CaseGenotypingMethod: Genomic DNA was extracted from patient fibroblasts, sequenced, and the three MCEE/thirteen MUT exons were analyzed and amplified. Any reported mutations were resequenced from fresh PCR product.

Variant: NM_032601.4(MCEE):c.178A>C (p.Lys60Gln)

ClinVar: 203812, https://www.ncbi.nlm.nih.gov/clinvar/variation/203812/

gnomAD: 0.01463 (10 homozygotes), https://gnomad.broadinstitute.org/variant/2-71351536-T-G

CaseDOIII-3: Female, 12 yrs report, White

CasePresentingHPOs: HP:0001531, HP:0002020, HP:0001942, HP:0001944, HP:0002789, HP:0002013, HP:0002014, HP:0002919, HP:0012120 (Failure to thrive in infancy, Gastroesophageal reflux, Metabolic acidosis, Dehydration, Tachypnea, Vomiting, Diarrhea, Ketonuria, Methylmalonic aciduria)

HPOsFreeText: Elevated methylcitric acid

CaseNotHPOs: N/A

NotHPOsFreeText: N/A

CaseAddInfo: Parents are first-cousin consanguineous, Son is healthy but second daughter shares phenotypes with the proband and shows clear methylmalonic aciduria, Proband and her sister are confirmed homozygous for this variant via parental testing

CasePreviousTesting: Serum methylmalonic acid was 1314 ng/ml (normal < 32); Vitamin B12 levels were normal (927 pg/ml, normal 200–1100); Vitamin B12 injections improved patient condition; At 12.5 yrs carnitine, plasma AAs, blood counts, and basic metabolic panels are normal but methylmalonic acid remains high at 180–1456 mmol/mol creatinine; Fibroblasts showed normal AdoCbl synthesis, contrary to expected from MMAA or MMAB variants; MUT and MMAB were sequenced with no variation found

CaseGenotypingMethod: Genomic DNA was isolated and PCR-amplified before directly sequencing all exons and flanking intronic sequences of the MCEE gene. Restriction enzyme digest confirmed the phase of the variant in the proband and the parents.

Variant: NM_032601.4(MCEE):c.139C>T (p.Arg47Ter)

ClinVar: 2343, https://www.ncbi.nlm.nih.gov/clinvar/variation/2343/

gnomAD: 0.0004884, https://gnomad.broadinstitute.org/variant/2-71351575-G-A

CaseDOIII-3: Female, 12 yrs report, White

CasePresentingHPOs: HP:0001531, HP:0002020, HP:0001942, HP:0001944, HP:0002789, HP:0002013, HP:0002014, HP:0002919, HP:0012120 (Failure to thrive in infancy, Gastroesophageal reflux, Metabolic acidosis, Dehydration, Tachypnea, Vomiting, Diarrhea, Ketonuria, Methylmalonic aciduria)

HPOsFreeText: Elevated methylcitric acid

CaseNotHPOs: N/A

NotHPOsFreeText: N/A

CaseAddInfo: Parents are first-cousin consanguineous, Son is healthy but second daughter shares phenotypes with the proband and shows clear methylmalonic aciduria, Proband and her sister are confirmed homozygous for this variant via parental testing

CasePreviousTesting: Serum methylmalonic acid was 1314 ng/ml (normal < 32); Vitamin B12 levels were normal (927 pg/ml, normal 200–1100); Vitamin B12 injections improved patient condition; At 12.5 yrs carnitine, plasma AAs, blood counts, and basic metabolic panels are normal but methylmalonic acid remains high at 180–1456 mmol/mol creatinine; Fibroblasts showed normal AdoCbl synthesis, contrary to expected from MMAA or MMAB variants; MUT and MMAB were sequenced with no variation found

CaseGenotypingMethod: Genomic DNA was isolated and PCR-amplified before directly sequencing all exons and flanking intronic sequences of the MCEE gene. Restriction enzyme digest confirmed the phase of the variant in the proband and the parents.

Variant: NM_032601.4(MCEE):c.139C>T (p.Arg47Ter)

ClinVar: 2343, https://www.ncbi.nlm.nih.gov/clinvar/variation/2343/

gnomAD: 0.0004884, https://gnomad.broadinstitute.org/variant/2-71351575-G-A