Examination of Huntington's disease with atypical clinical features in a Bangladeshi family tree.

Atypical manifestation of Huntington's disease (HD) could inform ongoing research into HD genetic modifiers not present in the primarily European populations studied to date. This work demonstrates that expanding HD genetic testing into under-resourced healthcare settings can benefit both local communities and ongoing research into HD etiology and new therapies.

Prior to enrollment, written informed consent was obtained from all study participants. The study was approved by the Ethical Review Committee (ERC) of Bangladesh Medical Research Council (BMRC).

Here, we describe an extended family in northern Bangladesh with eight members affected with Huntington's disease (HD) exhibiting atypical clinical features. All eight have the CAG repeat expansion in exon 1 of HTT gene and do not carry mutations associated with other HD‐like disorders, Wilson's disease, or other neurodegenerative diseases. The affected family, in northern Bangladesh, has eight living members with Huntington's disease (HD), all with atypical clinical features. The disorder appeared almost 130 years ago in one of the two siblings. All affected individuals are progeny of the affected sibling, and no progeny of the healthy sibling are affected. No consanguineous marriages are reported for the study participants. The age of onset decreased from 65 to 20 years over five generations, and this information is consistent with Huntington's disease. Clinical information was obtained for all eight patients. All of the patients (100%) exhibited mild jerky movement of fingers and slow movement of eyes as the first detectable clinical symptoms. Four of the patients (50%) exhibited moderate‐to‐severe chorea, whereas the remaining four cases (50%) did not exhibit any choreatic movement disorder except mild jerky movement of fingers and slow movement of eyes. All eight patients (100%) seemed normal in terms of cognitive function because there was no significant dementia as manifested by mini‐mental state examination. In addition, none of the patients did show any psychiatric disturbances. Although three cases (37.5%) showed characteristic features of anxiety, there was no tendency of committing suicide. It is mentionable here that one patient had severe chorea characterized by balanced trouble, clumsiness, tremor, significant weight loss, fidgeting, facial grimaces, increased appetite, less control over handwriting, rigidity, speech difficulties, grunting and abnormal speech patterns, inability to control speed and force of movement, general weakness, and impairment of superficial sensation. However, the clinical symptoms, as manifested by brain imaging and mini‐mental state examination, were not fully consistent with typical Huntington's disease (HD) or any other choreatic movement‐associated neurodegenerative diseases including HD‐like disorders or Wilson's disease. Analysis of blood parameters like total bilirubin, ALT (alanine aminotransferase), and ceruloplasmin as well as Kayser–Fleischer (K‐F) ring test did not show any abnormal results (data not shown), excluding the possibility Wilson's disease. MRI examination of the patient's brain did not reveal pathology typical of Huntington's disease (Fig. 1) 1, 2. Putamen and Caudate are the primary sites to be affected for the structural changes in Huntington's disease. No changes were evident in the caudate nucleus and striatum regions like putamen and globus pallidus, although mild cerebellar atrophy was observed (Fig. 1).

Figure 1

A representative brain MRI examination of patient with severe choreatic movement disorder. Bioimages of brain were obtained using the 1.5 T MRI systems (GE Healthcare, UK), with transverse T1‐ and T2‐weighted scans at the level of basal ganglia. (A) indicates T1‐weighted scan, whereas (B) indicates T2‐weighted scan.

Because of the atypical clinical symptoms, genetic testing using DNA specimens was used to diagnose the disorder. We first used PCR‐based method to check the length of the HTT allele 3. All four unaffected subjects tested had typical HD allele length of 80–85 bp, while all affected individuals were heterozygous, with one normal HD allele and one expanded allele (Fig. 2A). We used Sanger DNA sequencing to show that the normal allele had 20 CAG repeats, within the previously reported range of 6–35 4, 5. The expanded allele had either 53 CAG repeats (seven patients) or 70 CAG repeats (one patient), confirming the diagnosis of Huntington's disease (Fig. 2A and B) 6, 7, 8, 9. The patient with the longer CAG repeat was just 20 years of age and thus was diagnosed as juvenile HD 10, 11, 12. We found no mutations in three genes (PRNP, JPH3, and TBP) associated with HD‐like diseases HDL 1, HDL 2, and HDL 4, respectively (data not shown). Major clinical characteristic of typical Huntington's disease (HD) is manifested by progressive dementia. However, HD chorea without dementia 13, 14, 15 and absence of observable atrophy of either cortx or basal ganglia 16 have been reported. Although CAG repeat length can be correlated with some of the phenotypic variability like age of onset and disease severity 17, 18, 19, other genetic modifiers like loci 4p16 (LOD 1.93), 6p21–23 (LOD 2.29), and 6q24–26 (LOD 2.28) may influence the expression of HD 20.

Figure 2

DNA‐based analysis of patients’ specimens. (A) Agarose gel (2.0%) electrophoresis of human HTT gene polymerase chain reaction products of eight different patients and four healthy controls. Following electrophoresis, the PCR‐amplified products were stained with GelRed™ (Biotium Inc., Hayward, CA, USA) and photographed under UV light. Lanes 1 and 10 denote 1 kb+ Ladder (Thermo Fisher Scientific (Fermentas)); *(lanes 2–9) indicates affected individuals, ♦(lanes 11–14) indicates unaffected individuals, and lane 15 denotes template of negative control. (B) A representative partial sequencing chromatogram for a HD‐suspected patient. Gel‐extracted PCR product was used for Sanger DNA sequencing.

This extended family pedigree from northern Bangladesh exhibited an atypical, undiagnosed neurodegenerative disease. Using genetic sequencing, we diagnosed Huntington's disease. Although there are no HD‐specific treatments available yet, the affected people can now receive symptoms‐specific intervention to reduce the severity of the disease. In addition, genetic counseling can now help members of this family make informed reproductive decisions. This is the first study on diagnosis of a neurodegenerative disease using a sequencing‐based approach in Bangladesh, paving the way for expansion of facilities for diagnosis of other genetic disorders. Furthermore, the atypical manifestation of HD in this Bangladeshi family could inform ongoing research into HD genetic modifiers not present in the primarily European populations studied to date. This work demonstrates that expanding HD genetic testing into under‐resourced healthcare settings can benefit both local communities and ongoing research into HD disease etiology and new therapies.

Conflict of Interest

All authors declare no conflicts of interest to report this manuscript.

Authorship

Sequencing of purified PCR products was carried out by Dr. Regina LaRocque. Data compilation and initial manuscript writing were carried out by Md Mahfuz Al‐Mamun. MKM and EKK edited the manuscript. MMM and SKS together performed laboratory experiments and assembled the figures, while KM helped in troubleshooting. MMM and SKS contributed equally in terms of performing laboratory experiments and other works. SKQ, TS, MA, NS, and FQ contributed to design the experiments and upgrade the manuscript. KDM helped MRI image interpretation.