Spinocerebellar Ataxia Type 2 With Onset at Toddlerhood
An 8-year-old girl, born of nonconsanguineous marriage, developed insidious-onset, progressive imbalance while walking from 2 years of age. Simultaneously, she also developed progressive incoordination of the hands causing difficulty in eating, writing, and daily activities. The symptoms heightened with activity and subsided with rest. There was no history of cognitive decline, behavioral problems or vision impairment. She had a positive family history of a similar illness. Multiple family members were affected (Fig. 1) and each subsequent generation was affected at an earlier age, suggesting an autosomal-dominant inheritance with anticipation.
She had a normal general physical examination. Her memory was intact, but she had a scanning speech. She had oculomotor apraxia, saccadic overshoot, normal fundi, generalized mild hypotonia, dysmetria, dysdiadochokinesia, and intention tremors. Gait examination revealed truncal and limb ataxia. Rest of the neurological and systemic examination was unremarkable. Examination of the parents was noncontributory. A clinical diagnosis of autosomal-dominant spinocerebellar ataxia (SCA) with variable penetrance and anticipation was considered. Magnetic resonance imaging of brain showed cerebellar atrophy with prominent folia (Fig. 2). Metabolic screen (including tandem mass spectroscopy/gas chromatography), lipid and immunoglobulin profile, serum α-feto-protein, nerve conduction study, and brainstem-evoked response audiometry were normal. Polymerase chain reaction–based fragment analysis revealed expanded (>35) CAG trinucleotide repeats in ATXN2 gene confirming the diagnosis of SCA type 2.
Autosomal-dominant inheritance pattern with anticipation is the hallmark of SCA as in the index case. However, the mean age of the onset of SCA type 2 is commonly third to fourth decade, and onset in childhood is rare and atypical. Less than 20 cases of SCA type 2 in children have been reported worldwide, with the youngest case at 3 months of age.1 Although SCA type 2 has been reported as the most common cause of inherited ataxia in adults,2 it has been sparingly described in Indian children because of the variable phenotype; poor index of clinical suspicion; triplet expansion of reduced penetrant allele inherited from asymptomatic parent as in our index child; and lack of genetic testing.3 A good history elucidating the involved family members is crucial for clinical suspicion and needs confirmation by genetic testing. Children with SCA type 2 need regular follow-up as the full phenotypic spectrum may not be evident at presentation as in the index case and further neurological signs may evolve with time.