ADCY5-related dyskinesia: Broader spectrum and genotype-phenotype correlations

Abstract

Objective: To investigate the clinical spectrum and distinguishing features of adenylate cyclase 5 (ADCY5)-related dyskinesia and genotype-phenotype relationship.

Methods: We analyzed ADCY5 in patients with choreiform or dystonic movements by exome or targeted sequencing. Suspected mosaicism was confirmed by allele-specific amplification. We evaluated clinical features in our 50 new and previously reported cases.

Results: We identified 3 new families and 12 new sporadic cases with ADCY5 mutations. These mutations cause a mixed hyperkinetic disorder that includes dystonia, chorea, and myoclonus, often with facial involvement. The movements are sometimes painful and show episodic worsening on a fluctuating background. Many patients have axial hypotonia. In 2 unrelated families, a p.A726T mutation in the first cytoplasmic domain (C1) causes a relatively mild disorder of prominent facial and hand dystonia and chorea. Mutations p.R418W or p.R418Q in C1, de novo in 13 individuals and inherited in 1, produce a moderate to severe disorder with axial hypotonia, limb hypertonia, paroxysmal nocturnal or diurnal dyskinesia, chorea, myoclonus, and intermittent facial dyskinesia. Somatic mosaicism is usually associated with a less severe phenotype. In one family, a p.M1029K mutation in the C2 domain causes severe dystonia, hypotonia, and chorea. The progenitor, whose childhood-onset episodic movement disorder almost disappeared in adulthood, was mosaic for the mutation.

Conclusions: ADCY5-related dyskinesia is a childhood-onset disorder with a wide range of hyperkinetic abnormal movements. Genotype-specific correlations and mosaicism play important roles in the phenotypic variability. Recurrent mutations suggest particular functional importance of residues 418 and 726 in disease pathogenesis.

Figure 1. Organization of ADCY5 and locations of mutations

(A) Schematic of ADCY5 exons shows the number of families with each mutation (in parentheses) and the positions of some intragenic short tandem repeat markers (STRPs) and single nucleotide polymorphisms included in the haplotype analysis of the EHC and FDFM families. Markers in green rectangles define distinct haplotypes not shared by the 2 families. Genotypes of flanking STRPs D31271, D3S1278, D3S3606, D3S1292, and D3S1569 were also used (not shown). Mutations seen in multiple affected persons are in red and those identified only in a single individual are in green. In Chen et al., p.R418 was placed near the end of the sixth helix of the first transmembrane domain; the current consensus is that this residue is in the C1a domain. (B) ADCY5 protein contains 2 membrane-spanning and 2 major bipartite cytoplasmic domains. Binding of dopamine to the excitatory dopamine 1 receptor (D1R) activates the striatal stimulatory heterotrimeric G protein Gα_OLF that in turn activates ADCY5. On activation, the C1a and C2a regions of ADCY5 form a catalytic pocket in which conversion of adenosine-5ʹ-triphosphate (ATP) binding to 3′,5′-cyclic adenosine monophosphate (cAMP) occurs. EHC = essential hereditary chorea; FDFM = familial dyskinesia with facial myokymia. Modified from Chen et al. with permission (copyright © 2014 American Neurological Association).

Figure 2. Pedigrees of 2 families with mutations in ADCY5

Asterisks denote individuals who provided DNA samples and all of these who were affected were examined. The family-specific mutation segregated completely with affectation status; no nonmanifesting carriers were identified. Age at death (d) or current age (c) is shown. (A) Family EHC with autosomal dominant essential chorea and p.A726T ADCY5 mutation, updated from the diagram published in 1976. Medical records of individuals II-2 and III-3 had been reviewed and individual IV-3 had been examined previously. Individual VI-8 was examined but not sampled. Clinical descriptions of III-4, IV-5, and V-5 were detailed previously (denoted II-3, III-5, and IV-2). (B) Family ChDys, first described in 1967, with severe chorea and dystonia and p.M1029K ADCY5 mutation. In individual II-2, the mutation was detectable only by allele-specific amplification. EHC = essential hereditary chorea; ChDys = chorea-dystonia.

Figure 3. Allele-specific amplification documents mosaicism of ADCY5 mutations in representative cases

Wild-type (wt) alleles (top panels) were amplified using wt-primer and mutant alleles (lower panels) amplified using primers containing the mutant nucleotide in the 3′ position and one mismatched nucleotide in the preceding position. (A) Sequence chromatograms for 2 members of the ChDys family. The mutant nucleotide A is detected in patient III-6 but not in her affected mother II-2. Allele-specific PCR in II-2 amplified the mutant allele from blood, skin, and fibroblast cells. The analysis is not quantitative, but the very faint mutant band in fibroblasts suggests a selective advantage for the wt allele during culture. (B) On the sequence chromatograms, in contrast to C and T peaks of equal intensity in ID016, much smaller signals are present for the mutant T allele in ID020, ID021, and ID027. Presence of the mutant allele was confirmed for all by allele-specific amplification. (C) Mosaicism for the mutant A nucleotide is shown for ID024, in contrast to the peaks of equal height for the wt and mutant alleles in ID018. In all panels, for the mosaics, the faint gel signals are consistent with the small mutant allele peaks in the chromatograms. Absence of a mutant allele in a normal control (NC) demonstrates the specificity of the allele-specific amplification. ChDys = chorea-dystonia.