*Corresponding author:Chloe Mak, Room 1124, 11/F, Block G, Kowloon West Cluster Laboratory Genetic Service, Department of Pathology, Princess Margaret Hospital, Hong Kong SAR, China
Received: May 13, 2018; Published: May 22, 2018
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Purpose: Huntington disease (HD) is a progressive and fatal autosomal dominant neurodegenerative disorder caused by trinucleotide CAG repeats in exon 1 of HTT.Incidence is lower among Chinese with limited data. We characterize the clinical and genetic data of six HD Hong Kong Chinese patients.
Materials and Methods: A total of 13 suspected cases were performed from 2008 to 2013. Repeat sizing was performed by PCR, agarose gel electrophoresis, fragment analysis by capillary electrophoresis and confirmed with Sanger sequencing. Triplet repeat primed PCR was performed for cases with one normal band detected. Reflex genetic testing of dentatorubral-pallidoluysian atrophy (DRPLA) was performed for all negative cases.
Results: Six were diagnosed of HD with CAG repeat > 40. Three positive cases had no HD family history. Two pre-symptomatic testing was performed with one positive. All symptomatic patients were adult onset with 43.4 ± 11.6 years (mean ± SD; range 29–59 years). The duration from onset to genetic testing was 7 ± 4.8 years (mean ± SD; range 0 – 12 years). The major clinical presentations were generalized chorea, behavioral disorders and dementia. The number of pathological expanded CAG repeats was 46 ± 6.8 (range 42 – 58).None of those with negative HD mutation were positive for DRPLA.
Conclusion: We have characterized the clinical and genetic data of six Huntington disease Hong Kong Chinese patients. All were adult onset and had CAG repeat > 40 and half had no HD family history. The duration from onset to genetic testing was significantly long. We have simplified the PCR protocols of triplet repeat primed PCR and Sanger sequencing without gel excision for expanded allele. We recommend reflex testing for other HD phenocopy conditions could be considered in patients with negative HD mutation.
Keywords: Hong Kong Chinese; Huntington Disease; HTT