Clinical features of familial Parkinson's disease in Thai patients.

Background: Parkinson's disease (PD) is the second most common neurodegenerative disease. Most cases are sporadic, but family history is also observed in certain cases. This study aimed to describe the clinical features of familial PD in Thai patients.

Method: The study included five female and three male patients from a Malay family of consanguineous parents who were evaluated for clinical study. Every patient was examined initially at the outpatient unit of the family medicine department. The diagnosis was later confirmed by a team of neurologists at the division of neurology, department of medicine. The patients were first seen and evaluated in 1999, with subsequent evaluation in 2005 and 2008.

Results: Clinical features such as tremor, rigidity, bradykinesia and postural instability were similar to those of the classical idiopathic PD, but age of onset was earlier. The interval between the onset of parkinsonism and first presentation was 1-3 years, and PD was diagnosed within 1-4 years of the onset of parkinsonism. The median age at disease onset was 31 years (range 27 to 49 years). The severity of clinical symptoms and signs was different among affected family members, from stage I to IV of the Hoehn and Yahr stage scale. Motor dysfunction and other complications were observed. The family history suggested that the condition was being passed on only from the maternal side.

Conclusions: The clinical features of familial PD are generally indistinguishable from classical PD, although the diagnosis may be difficult in atypical presentations such as palpitation, anxiety and insomnia. The disease tends to develop earlier in younger siblings. Family members were at greater risk of autosomal recessive disorders that are homozygous for a particular recessive gene mutation due to consanguineous parents. On the other hand, specific ethnicity, very early onset of symptoms, rapid progression of the disease, and high family incidence suggested autosomal dominant inheritance. Since each family member displayed different symptoms and signs, this may have indicated variable penetrance of the PD gene, but the results are not conclusive due to lack of medical records from other relatives and genetic studies.