A 33-year-old man was referred to the diabetes clinic with an 8-month history of weight loss and polydipsia. Two months previously his general practitioner had found a high fasting plasma glucose concentration of 17.5 mmol/L (3.0–6.0) and a haemoglobin A1c of 116 mmol/mol (20–42). The patient was taking metformin 1 g twice daily. He reported in the diabetes clinic that his home capillary blood glucose concentrations persisted to be high, ranging between 15–24 mmol/L.
On examination, his body mass index was 23 kg/m2 (18–25).
His blood tests were repeated in the diabetes clinic and he was treated with a basal bolus insulin regimen. Urinalysis was negative for ketones.
Investigations (in diabetes clinic):
haemoglobin A1c 110 mmol/mol (20–42)
serum C-peptide 200 pmol/L (180–360)
anti-glutamic acid decarboxylase (GAD)
antibodies 69 IU/mL (<10)
anti-IA2 antibodies negative
What is the most likely diagnosis?
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haemochromatosis
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latent autoimmune diabetes in adults
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maturity-onset diabetes of the young
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mitochondrial diabetes mellitus
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type 1 diabetes mellitus
