Juvenile Huntington’s disease in northern Brazil: a case series report

Introduction : Huntington’s disease (HD) is a neurodegenerative disorder caused by CAG expansion repeats in the HTT gene. Usually, the symptoms start to manifest in mid-adulthood. In about 5% of cases, however, the signs begin before the age of 20 years. These cases are known as juvenile HD (JHD). Objective : here we report a case series of JHD from Amazonas, a state where data are scarce due to the restricted access to specialized medical assistance for diagnosis and care. Case series : the patients were attended by neurologists specialized in movement disorders at Manaus. Two cases manifested the disease in childhood (6 and 7 years old) and two cases, in adolescence (12 and 16 years old). All cases showed dystonia and parkinsonism as predominant motor disorders. Moreover, signs of cognitive decline, depression, and psychosis were observed in all patients. Conversely, cerebellar signs, gait disturbances, seizures, and some psychiatric symptoms were variable among the cases. Expansion size varied from 66 to 84 to CAG repeats and the difference in age at onset between parent and child varied from 23 to 43 years. Conclusion : to our knowledge, these are the first clinical reports of JHD in northern Brazil. These cases illustrate the variability in clinical phenotypes and genetic features of JHD cases. Furthermore, they can contribute to the awareness of HD here, both by professionals and the public in general.


INTRODUCTION
Huntington's disease (HD) is a progressive neurodegenerative disorder, with an autosomal dominant inheritance. Clinically, HD is characterized by a triad of motor, cognitive and psychiatric symptoms 1 . Chorea is the hallmark motor sign of HD, which is characterized by involuntary, abrupt, and nonrhythmic movements because of random muscle contractions 2 . Age at onset is typically between 30 and 50 years. In about 5% of HD cases (with a range of 1-15%), however, disease onset is before 20 years old. These cases are known as Juvenile HD (JHD) 1,3 .
HD is caused by an expansion in the number of CAG repeats (≥ 36 repeats) within the first exon of the Huntingtin (HTT) gene 4 . The number of CAG repeats in the HTT gene has a strong negative correlation to the age when symptoms start to manifest. Also, these trinucleotide repeats are unstable when transmitted from parent to child, which leads mostly to expansion. Thus, there is a tendency to increase in CAG length in successive generations affected by HD, which, in turn, leads to age at onset progressively earlier within families. This phenomenon is known as anticipation. JHD is the case of extreme anticipation 1,4 .
Clinical manifestation of JHD is different than in adults. The common motor signs initially in juvenile forms are gait disturbances; oral-motor dysfunctions (such as speech/ swallowing disturbances); and parkinsonian features of bradykinesia, which is the slowness of movements, and rigidity, which refers to an increased muscle tone in both flexion and extension movements 2,5 . Cognitive impairments (such as declining in school performance and developmental delay) and behavioral changes are also common presenting symptoms in JHD. Also, in contrast to adult HD, the predominant motor symptoms in JHD are often parkinsonism and dystonia (i.e., an abnormal posture or twisting movements caused by sustained muscle contractions) 2,3 .
In around 80% of JHD cases, the expanded allele is inherited from the father. There is no specific CAG repeat range that defines a juvenile-onset. Individuals with CAG repeats > 60 usually show a disease onset before 20 years. However, there are JHD cases associated with repeat lengths below. The instability in CAG length that leads to larger expansions is greater in spermatogenesis than in oogenesis, which explains the predominance of paternal inheritance in JHD [3][4][5] . Moreover, JHD can be divided into two subgroups according to the age at onset: childhood-onset, with the presentation of first symptoms ≤10 years; and adolescent-onset, with initial manifestation between 11 and 20 years. Childhood HD is rarer, corresponding to about 20% of all JHD cases. Clinical and genetic features can be variable among these subgroups. The phenotypic variation and unspecific features cause difficulties in the diagnosis 3,5,6 .
Here we present a cases series of JHD in patients from northern Brazil. In this region, access to medical specialists (especially outside the capital cities) and genetic testing is very restricted. Thus, underdiagnosis and misdiagnosis of HD are serious public health problems. Here we described two cases with childhood-onset and two with adolescent-onset, comparing their clinical presentation, disease progression, and familial inheritance of expanded alleles.

Cases 3 and 4
Two siblings, one with 18-years-old (case 3) and the other with 28 (case 4), showed initial motor signs of bradykinesia followed by dystonia at ages seven and 16 (Figure 1c).

DISCUSSION
The juvenile form of HD may be presented at first within a wide range of clinical features. In the first two cases, cerebellar signs were reported as initial symptoms. Patient 1 showed falls at disease presentation. Gait disturbances are one of the most common first symptoms when HD initiates in childhood 5,6 . Also, this case manifested dysarthria as an early sign. Patient 2, in turn, showed loss of hand dexterity as one of his first symptoms, which is common in adolescent-onset cases 6 . Overall, cerebellar signs usually occur early in JHD, while they are seen only in later stages of disease progression in adult HD 8

. In patients 3 and 4, conversely, the first symptoms noticed were dystonia and bradykinesia.
At disease progression, parkinsonism (bradykinesia and rigidity) and dystonia were the predominant clinical features in all patients here, which is usual for JHD, in contrast to adult HD, as previously mentioned. None of our patients manifested signs of chorea. Chorea, when present in JHD, is usually not an early sign but occurs during the disease course 3 . There is evidence that the HD pathological process is more extensive in the brain of juveniles than in adult-onset cases. The atrophy of the globus pallidus is more severe in JHD, which might help to explain the predominance of the parkinsonism phenotype in such cases 9 . Conversely, seizures, which are symptoms that occur frequently in JHD cases, were observed in only one patient in our study (patient 2). There is evidence that the risk of seizures is inversely proportional to the age at onset, i.e., they are more common when the disease onset is in childhood 5,6 . Interestingly, no seizures were observed in the two childhood cases reported here.
Furthermore, gait disturbances are a common, but variable, clinical feature in JHD. In our cases, they were manifested in three distinct ways. Patient 1 showed unsteady gait and recurrent falls. In HD, falls are associated with both motor and cognitive symptoms. In the first case, they could be the result of a combination of bradykinesia, decreasing gait speed and step height; dystonic posture, interrupting the movement flow; and cognitive decline, making it difficult to walk while performing other cognitive tasks simultaneously 10 . Moreover, patient 3 showed a wide-based ataxic gait. Ataxia used to be considered an unusual symptom of HD. However, recent evidence demonstrated that gait ataxia and other ataxic signs are common in HD, possibly as the result of cerebellar degeneration during the disease course 11 . Interestingly, while a reduced velocity gait is typical of HD 10 , patient 4 presented a narrow-based festinant gait. Festination is the tendency to walk with increasingly rapid, but shorter steps while leaning the center of gravity forward. This kind of gait disturbance is typical of advanced stages of Parkinson's disease and parkinsonian syndromes 12 .
Non-motor symptoms were prevalent in all patients. The first case showed a cognitive impairment trait (learning difficulties at school) at disease presentation, while psychiatric problems (irritability/aggressive behavior) were predominant since early in the second one. All cases showed a considerable cognitive decline. Depression Rev. Ciênc. Méd. Biol., Salvador, v. 21, n. 2, p. 302-307, maio/ago. 2022 (4/4), psychosis (3/4), apathy (2/4), and aggressiveness (2/4) were psychiatric symptoms commonly reported. The importance of cognitive and psychiatric symptoms in HD since early in the disease course is being more recognized in recent studies. Still, non-motor features are considered more severe in earlier stages of JHD than in adult HD 5 . There is evidence that cognitive aspects related to developmental delay or regression are more common in childhood-onset cases, while psychiatric/behavioral deficits, in adolescent ones 5,8 . Moreover, psychotic symptoms are rarely reported in the adult form 8 .
It has been proposed that many clinical differences of JHD to adult HD are related to fact that the disease onset happens before the brain development process is finished. Thus, JHD manifestation is not only related to HD pathology but also to abnormal neurodevelopment 8 . In this way, many clinical characteristics of JHD overlap with neurodevelopmental disorders manifested in childhood and adolescence, such as cerebellar signs, seizures, and specific cognitive and behavioral problems 5 .
Furthermore, in our cases, CAG length in expanded alleles varied from 66 to 84 repeats and age at onset, from six to 16 years. CAG number is considered the most critical determinant of HD age at onset, especially in JHD cases. In a retrospective study with a large set of patients, Fusilli et al. 6 proposed that JHD could be divided into two subgroups according to their CAG length, each one with a typical set of clinical features: highly expanded (≥ 80 repeats), which exhibit a childhood-onset; and low expansion (< 80 repeats), which is associated to an adolescent-onset. Here, one childhood-onset case was compatible with the highly expanded subgroup (patient 3), while the other one presented a repeat number lower than expected (patient 1). Conversely, both adolescent-onset cases fitted in all aspects of the low expansion group. Interestingly, in our study, the lowest age at onset (6 years, patient 1) did not correspond to the highest CAG length (84 repeats, patient 3).
The expanded allele was paternally inherited in all our JHD patients, as expected. The increase in CAG repeats from father to child varied from +21 to +39. In previous studies about intergenerational instability of HD expanded alleles, the estimated increase of CAG number in usual juvenile-onset cases varied from -4 to +47 repeats 13 . The largest expansion registered so far from father to child was +211 CAG repeats, resulting in an expanded allele of 265 repeats, which is also the highest one reported for the HTT gene 14 . Recent experimental evidence has demonstrated that the male expansion bias in CAG length instability is driven by chromatin remodeling in post meiotic events that are specific to spermatogenesis. It has been proposed that DNA double-stand breaks formation and repair mechanisms during the chromatin remodeling process in haploid spermatids are processes that contribute to the male-specific genetic instability 15 .
In our study, anticipation varied from -23 to -43 years from father to child. Previous studies describing anticipation in JHD cases have reported a range of onset changes in parent to child transmissions of -7 to -35 years 13,16 . Even in the case of very large CAG expansions (>100) from parent to child transmissions, changes in the onset years are around -30 years 17 . Thus, the anticipation of 43 years observed here is very unusual. Interestingly, the intergenerational increase in CAG length was higher in patients 1 and 3 (+32 and +39, respectively), while anticipation was greater in patients 3 and 4 (43 and 34 years, respectively), which are from the same family. Although the anticipation phenomenon in HD is seen as the result of progressive CAG repeat expansion over successive generations, a large part of the change in age at onset from parent to child cannot be explained only by the intergenerational increase in CAG repeats. Given the trend towards the occurrence of multiple JHD cases within families, it has been suggested that there might be a familial component that increases the likelihood of juvenile cases in certain families, which could be the effect of either genetic factors or shared environments 18 .
In Brazil, the prevalence of JHD is unknown. However, the occurrence of these cases has been investigated in previous screening studies in Southern and Southeastern regions [19][20][21][22] . The proportion of juvenile-onset to total genetically confirmed HD cases ranged from 4% (3/75 cases) 19 to 12,5% (4/32 cases) 20 . Childhood-onset cases were observed in two studies 21,22 . The younger age at onset reported was 2 years old 22 , and the largest CAG length was 88 repeats 21 . To our knowledge, the JHD cases described here are the first ones reported in northern Brazil. Two of them were part of our previous report about HD occurrence in the referral center for movement disorders of Manaus/AM 23 . These patients represent 10,8% (4/37 cases) of total confirmed HD cases so far (personal communication). In Amazonas, there are only a few medical doctors that are specialists in movement disorders. Also, most families cannot afford genetic testing. This situation is aggravated by the lack of public awareness of this disease, even among clinicians. According to family reports, members of two or three generations (and possibly more) suffered from HD but were not diagnosed. Also, three of our patients lived outside Manaus, which was especially critical since they did not receive specialized help for many years after the disease started to manifest.

CONCLUSION
In summary, we presented the clinical and genetic aspects of four JHD cases from northern Brazil, a large region in which the access to diagnosis of rare conditions is very restricted, and data are scarce. Interestingly, these cases illustrate the variability in clinical phenotypes of JHD and the inheritance of expanded CAG repeats within families. Reports of HD and JHD cases in this region can contribute to disease awareness, both by professionals and the public, which can, in turn, potentially improve access to correct diagnosis, proper care, and genetic counseling for the affected families in the future.