A Rare Presentation of Friedreich’s Ataxia in Pediatric Case: Diabetes Mellitus

Introduction: Friedreich’s ataxia (FA) is an autosomal recessive neurodegenerative disorder resulting from a mutation of a gene locus on chromosome 9. The most common molecular abnormality is a GAA trinucleotide repeat expansion in intron 1 of the frataxin (FXN) gene; normal individuals have 5 to 30 GAA repeat expansions. FA is characterized by progressive gait and limb ataxia with associated limb muscle weakness, absent lower limb reflexes, extensor plantar responses, dysarthria, and decreased proprioception. Patients are at risk of getting glucose intolerance and 20% progress to overt diabetes. The cause of diabetes in FA is poorly understood. Diabetes can result from a shortage in insulin secretion, from a poor response to insulin (insulin resistance), or from a combination of both.
Case: A 15.5-year-old girl was admitted to the hospital with weakness, vomiting, weight loss, polyuria, and polydipsia in the last 1 month. History revealed the presence of gait disturbance and pain in soles for 3 years. On physical examination, cachexia, dehydration, and ketonemic odor were noted. Thyroid gland was soft and bilaterally 4 cm on palpation. Neurological examination demonstrated ataxic gait pattern, pes cavus, intentional tremor, lower limb areflexia, and flexor plantar response. Blood glucose was 390 mg/dL with ketonuria but without acidosis. Insulin and c-peptide levels were 1.53 µIU/mL and 1.08 ng/mL, respectively, and HbA1c was 13.4%. She was treated with subcutaneous insulin. Glutamic acid decarboxylase, insulin, and antiislet cell antibodies were negative. No cardiomyopathy was detected by echocardiography. Hyperthyroidism was detected [thyroid-stimulating hormone (TSH) 0.03 µU/mL (0.34-5.6), free thyroxine 1.79 ng/dL (0.61-1.12), free triiodothyronine 4.57 pg/mL (2.5-3.9)] with negative thyroid autoantibodies. FXN gene analysis revealed more than 66 GAA trinucleotide repeats in intron 1 which is a homozygous state and consistent with FA.
Conclusion: FA must be considered in patients who presented with diabetes and ataxia. In our case, for the first time, non-autoimmune hyperthyroidism was detected in FA.