The constellation of ataxic gait, nystagmus, dysarthria, and pes cavus in a young adolescent is characteristic of Friedreich's ataxia. Friedreich's ataxia is an autosomal recessive disorder, with each child having a 25% chance of having clinical manifestations of the disease and a 75% chance of not having clinical disease. Thus, the patient's brother would most likely have a normal physical exam.
Friedreich's ataxia is an autosomal recessive trinucleotide repeat disorder (GAA) that leads to mutation of the frataxin gene. The frataxin gene is essential in mitochondrial iron regulation, and impairment of mitochondrial functioning results in cerebellar and spinal cord degeneration. Onset of Friedreich's ataxia is typically between 8-15 years of age, with gait ataxia being the usual presenting symptom. Physical exam may also reveal nystagmus, dysarthria, decreased vibratory and proprioceptive senses, and musculoskeletal findings such as kyphoscholiosis and pes cavus. Hypertrophic cardiomyopathy develops in more than 50% of patients, with cardiac arrhythmia and congestive heart failure as the cause of death in many patients with Friedreich ataxia.
Hamilton reviews an appropriate evaluation in children presenting with symptoms of coordination problems. Although "developmental coordination disorder” has been used to describe children with minor motor difficulties, it is important to differentiate this disorder from an organic cause of the child's incoordination. Specifically, symptoms such as weakness, ataxia, and pronounced hypotonia or hypertonia - particularly when asymmetric - should compel the physician to expand the diagnostic possibilities.
Anheim et al. provide a review of the autosomal recessive cerebellar ataxias. They highlight Friedreich's ataxia as the most frequent autosomal recessive cerebellar ataxia and characterize the disorder by both cerebellar and proprioceptive ataxia, areflexia, and extensor plantar reflexes. Because of its frequency, Friedreich's ataxia should be suspected in Caucasians and people from the Indian subcontinent with ataxia.
Figure A depicts pes cavus, or a high arch of the foot that does not flatten with weight bearing. Friedreich's ataxia may cause muscle imbalances that leads to elevated arches. Illustration A depicts kyphoscoliosis, an abnormal curvature of the spine in both a coronal and sagittal plane
Answer 1. A systolic ejection murmur is characteristic of hypertrophic cardiomyopathy, a common cause of death in patients with Friedreich ataxia.
Answer 2. Telangiectasia may be seen in ataxia-telangiectasia, an autosomal recessive disorder characterized by progressive neurologic impairment, cerebellar ataxia, and ocular and cutaneous telangiectasia.
Answer 3. Mental retardation is a finding in many congenital disorders. The most common cause of inherited mental retardation is Fragile X Syndrome, which results from a trinucleotide repeat expansion of CGG.
Answer 4. Pes cavus is a frequent physical finding in FA, which is characterized by a foot sole that is hollow when bearing weight, resembling a high arch.
Hamilton SS. Evaluation of clumsiness in children. Am Fam Physician. 2002 Oct 15;66(8):1435-40, 1379.
PMID:12408418 (Link to Abstract)
Anheim M, Tranchant C, Koenig M. The autosomal recessive cerebellar ataxias. N Engl J Med. 2012 Feb 16;366(7):636-46. doi: 10.1056/NEJMra1006610.
PMID:22335741 (Link to Abstract)
USMLE World Step 1 QBank Question #672. Copyright © USMLEWorld, LLC 2012