The symptoms differed between the group of patients who were below ten years of age at onset and those who were ten or older. The most common presenting symptoms in the younger group were cognitive problems such as declining school performance, regression in language skills, or an inability to learn to read. The most common presenting symptom in the older group was oropharyngeal dysfunction. (The oropharynx consists of the back third of the tongue, the soft palate, the tonsils, and the side and back walls of the throat.
Two of the five older patients also had cognitive problems at onset and two in the younger group had oropharyngeal dysfunction. Two in each group had fine motor problems, one in each had behavioral problems, and two of the younger group and one in the older had gait problems.
Ten out of the twelve patients developed oropharyngeal problems sometime during the course of the disease. Ten out of twelve developed upper motoneuron symptoms (increased reflexes, spasticity, Babinski sign). Four out of seven of the younger group developed seizures but none of the older group did. Although other studies associate dystonia (rigidity) with the earlier JHD onset and chorea with later JHD onset, this was not the case in this study. Chorea was not a presenting symptom for any of the children but developed in five of the seven earlier onset cases and in two of the five later onset cases. Dystonia was not a presenting symptom but developed in two of the seven earlier onset cases and one of the five later onset cases. IQ tests were performed repeatedly for four patients and all four showed decline over time.
Ten of the patients had received EEGs. Eight were abnormal and two were normal. Some of the patients' brains appeared to be normal under imaging (PET or MRI) a year after onset but all showed abnormalities two years after onset.
The most frequent heralding symptom was cognitive decline in the group with earlier onset and oropharyngeal dysfunction in the later-onset group. Seizures occurred only in the younger age at onset group. Chorea was not a presenting sign but developed later in the course of the disease and, with dystonia, was more prevalent in the early age at onset group, whereas rigidity and bradykinesia were more prevalent in the older age at onset group. Patients in both groups developed gait, cognitive, and behavioral disorders at some point during the course of the disease. Furthermore, a slow and steady decline in IQ was observed on serial neuropsychologic testing in patients from both groups. Imaging studies were normal early and most commonly revealed neostriatal atrophy later in the course of the disease.
In this report, we describe the characteristics of 12 patients with childhood-onset Huntington disease and review those previously reported, expanding our knowledge about the features of childhood-onset Huntington disease, underlining the differences with patients with adult-onset Huntington disease, and suggesting a differential phenotype within patients with childhood-onset Huntington disease depending on the age at onset.