I.V. was born to Italian non consanguineous parents on the 23rd October of 1990.She was first evaluated at theage of 30 days when she presented with recurrent vomiting with every meal (exclusive breast feed), diarrhea and weight loss (< 25% percentile). She was born from eutocic birth with a weight of 3,300 g (50th percentile), head circumference 34.5 cm (50th percentile), length 50 cm (50th percentile).
Family history revealed a sister who died at the age of 3 months with a similar clinical syndrome and with pancytopenia. This sibling was diagnosed an acute myeloid leukemia, but the diagnosis was not confirmed at post-mortem examination.
On admission to the hospital our patient showed pallor, recurrent vomiting at every meal, diarrhea but clinical examination, including neurological evaluation, was otherwise normal.
Complete blood count (CBC) revealed megaloblastic anemia with leukopenia as reported in Table 1.
Table 1
Red Blood Cell Count (RBC) | 2,040,000/µL |
Hemoglobin (Hb) | 7.5 g/dL |
Hematocrit (Ht) | 23.5% |
Mean Corpuscular Volume (MCV) | 115.2 fL |
Mean Corpuscular Hb (MCH) | 36.8 pg/cell |
MCH concentration (MCHC) | 31.9 g/dL |
White Blood Cell Count (WBC) | 5400/µL |
-neutrophils | 12% |
-lymphocytes | 83% |
-monocytes | 5% |
-platelet count | 165,000/µL |
Peripheral blood film showed hypochromic macrocytic Red Blood Cells (RBC) and hyper-segmented neutrophils, with no reticulocytosis. Folate and cobalamin blood concentrations were normal (19.2 mg/mL and 1940 pg/mL respectively). Urinary spot methylmalonic acid (qualitative) was not elevated, while homocystinuria was present.
The clinicalpicture,includingfamily history, and laboratory findings suggested the diagnostic suspect of a methylation deficiency of B12.
Treatment was started with several transfusions of washed and concentrated RBC and intramuscular (IM) injections of hydroxocobalamin (1 mg/day for 1 week and then 1 mg twice a week).The clinical picture progressively improved with disappearance of vomiting and diarrhea, normalizationof blood tests and body growth.
When she was 8 years old an attempt to suspend treatment for three months was unsuccessful causing the reappearance of megaloblastic anemia. IMhydroxocobalamin needed to be restartedsine die. Menarche started at the age of 10 years and half. In the last pediatric examination at the age of 16 years, normal growth and development were observed (weight 50 kg, height 150 cm, body mass index 21.65). Cardiovascular and neurological examinations, including ECG and EEG, were normal. Dual-energy X-ray absorptiometry was within normal limits. Blood tests showed a persistent normalization of the CBC and related indices: RBC 4,570,000/µL, Hb 14.8 g/dL, MCV 88 fL, WBC 6,600/µL, platelets 261,000/µL.
At present time in 2020 she is a 30-year old healthy lady taking 1 mg of IM hydroxocobalamin once a week (Table 2).
Table 2
Age | Symptoms | Blood Analysis | Diagnosis | Treatment | Outcome |
30 days | -Pallor -Recurrent vomiting at every meal -Diarrhea -Weight loss (< 25th percentile) | -Megaloblastic anemia -Normal Folate and cobalamin blood concentrations -Urinary spot methylmalonic acid normal homocystinuria present | At 45 day a suspected transcobalamin 2 deficiency was diagnosed | Several transfusions of washed and concentrated RBC and IM injections of hydroxocobalamin (1 mg/day for one weeks and thereafter 1 mg/ twice a week) | -Vomiting and diarrhea disappearance -Blood test normalization -Body growth normalization |
11 months | Any symptoms | -Normal hematological picture | | IM injections of 1 mg/week of hydroxocobalamin | -Excellent health -Body weight (between the 50th and 75th percentiles) |
8 years | Any symptoms | -Normal hematological picture | | Therapy suspension for three months | Megaloblastic anemia reappearance |
8 years | Any symptoms | -Megaloblastic anemia | | Therapy resumption IM injections of 1 mg/week of hydroxocobalamin | Hematological picture normalization |
10 years and half | Appearence of menarche | | | | |
29 years | Any symptoms | -Normal hematological picture | Genetic confirmation of TCN2 mutation | IM injections of 1 mg/week of hydroxocobalamin | Good health |
At present | Any symptoms | -Normal hematological picture | | IM injections of 1 mg/week of hydroxocobalamin | She is a 30 years old healthy lady |
At 29 years of age the patient underwent definitive genetic diagnosis and therefore weanalysed the sequence of the gene TCN2 (NM_000355.3). We found a c.1114_1115delAC deletion in homozygosity at the exon 8 level, which determines a frameshift or slippage of the reading module, with consequent incorrect translation of TC protein. The wild type (wt) TC protein is 427aa long, the mutated protein has the identical amonoacidic (aa) sequence until 372aa and then introduces 37aadifferent from wt protein, and a stop codon that truncated the protein at 409aa (Fig. 1).
We also found a single nucleotide variant in homozygosity A > G in the first exon region (rs2240433).
Diagnostic Assessment
Blood count, RBC indexes and biochemistry were performed by routine methods. Serum was frozen following centrifugation and thawed for further studies. TCN2 of the gene sequence analysis was performed by Genechron S.r.l.
Folate, methylmalonic acid blood concentrations and homocystinuria were evaluated using standard procedures.
B12 was measured by radio-immunoassay, and B12 absorption was evaluated by the Schilling test with 1 mg of B12.