1 Introduction

Migraine is the most common neurological disorder presented often (∼30 % cases) with aura which is associated with sensory and motor disturbances. Familial hemiplegic migraine (FHM) is a rare monogenic type of migraine with aura for which several genes have been identified [1]. Each type of FHM is associated with mutations in representative gene. For example, mutations in CACNA1A are found in FHM1 [2]. Out of all these mutation, T666M was found in 40–50 % FHM1 cases [2, 3]. Also, mutations R1347Q and I1811L were found in several families with FHM1 [4]. More than 60 mutations in the gene ATP1A2, coding for α2 subunit of the glial and neuronal Na+/K+-ATPase, were found in FHM2 and sporadic migraine [2, 5–9]. It has been shown that, mutations in SCN1A gene, coding for α1 subunit of voltage-dependent Na+ channels, may cause FHM3. Currently, few mutations in these genes are identified [10–14].

In this study, the presence of known mutations in CACNA1A, ATP1A2, and SCN1A genes was investigated in three generations of FHM Tatar cases. Analysis revealed lack of mutations associated with FHM, suggesting novel mutations in cases studied. Further genetic analysis of the complete genome of Tatar FHM cases may reveal previously unknown mutations related to the disease pathogenesis.

2 Material and Methods

Blood samples collected from the four patients of the FHM family were used for DNA extraction (Lytech, Russia). The Institutional Review Board of the Kazan Federal University approved this study, and informed consent was obtained from each study subject according to the guidelines approved under this protocol (article 20, Federal Law “Protection of Health Right of Citizens of Russian Federation” N323–FZ, 11.21.2011). Informed consent for this publication was obtained from the living patients. DNA samples were analyzed for the presence of mutations in genes known associated with FHM, i.e., CACNA1A, ATP1A2, and SCN1A, using polymerase chain reaction (PCR). One microliter of DNA (25 ng) was mixed with 2 μL 10× PCR buffer, 2 μL 25 mM MgCl2, 0.2 μL (100 pM) of each primer, 0.8 μL 25 mM dNTP, 13.3 μL LH2O, and 0.5 μL (2.5 U) Taq DNA polymerase (Sileks, Russia). Amplification was performed as follows: (1) DNA denaturation at 95 °C, 5 min; (2) 40 cycles at 95 °C, 30 s; 56 °C (for CACNA1A exons 4, 16, 17, 25, and 36 and ATP1A2 exons 9, 10, 15, 16, and 23) or 53 °C (for SCN1A exons 6, 17, and 23), 30 s; 72 °C, 25 s (for CACNA1A), 45 s (for ATP1A2), or 40 s (for SCN1A); (3) final extension at 72 °C, 5 min; (4) reaction termination at 4 °C. PCR products were sequenced using 3730 DNA Analyzer (Life technologies, Carlsbad, CA, USA). Analyzed mutations in CACNA1A, ATP1A2, and SCN1A genes are summarized in Table 1. Primers used for PCR amplification and sequencing analysis are summarized in Table 2.

Table 1 Genes and tested amino acid changes (mutations) in our FHM patients
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Table 2 Primers used for PCR amplification and sequencing analysis
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3 Results and Discussion

The Tatar family involved in this study included 13 individuals, where four members were diagnosed with FHM at the regional neurological hospital. These patients include father (patient F; proband) and his brother (patient B), as well as the daughter (patient D) and son (patient S) of patient F. Severe clinical presentation of FHM was characteristic to proband and his brother. Both patients had headache lasting for several hours, accompanied by nausea and intolerance to light and sound. Migraine attacks appeared 2–3 times per year during the last 30 years. Notably, clinical symptoms of FHM were mild in patient S, which were limited to a single pulsation headache attack without clear aura.

Presence of mutations in CACNA1A, ATP1A2, and SCN1A genes, previously shown associated with FHM, was analyzed to establish the genetic predisposition to the disease. A total of 12 exons in three genes were analyzed using PCR. Analysis included four exons 4, 16, 17, 25, and 36 in the CACNA1A gene, encoding for the α1A subunit of voltage-gated Cav2.1 calcium channels. Missense mutations R192Q, T666M, V714A, R1347Q, and I1811L had been previously found in FHM [4, 15–17]. Additionally, the exons 9, 15, 16, and 22 in the ATP1A2 gene were analyzed. The ATP1A2 gene codes for the α2 subunit of Na+/K+-ATPase, where several mutations (T378N, R689Q, N717K, M731T, and D999H) were found in FHM cases [5–9, 18]. Finally, Tatar FHM cases studied were examined for the presence of mutations in the exons 6, 17, and 23 of the SCN1A gene, coding for the α1 subunit of voltage-gated sodium channel Nav1.1. Amino acid-altering mutations in these exons (L263V, T1174S, and Q1489K) were previously found in FHM cases [11–14]. Interestingly, Tatar FHM cases lack previously described mutations in these exons. However, there was a single nucleotide substitution identified in CACNA1A gene in patients F, B, and D at the third position of the codon 698 (ACG to ACA), which did not cause amino acid change. Additionally, silent mutation was identified in ATP1A2 gene (codon 373; TCG→TCA) in patients F and S (Fig. 1)

Fig. 1
figure 1

a Electrophoregram of sequences of exon 16 of the gene CACNA1A. Left—with a mutation of G→A, right—control. b Electropherogram of sequences of exon 9 of the gene ATP1A2. Left—with a mutation of G→A, right—control

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. Mutations previously shown to be associated with FHM were absent in the Tatar cases. Similar to our results, absence of known mutations in FHM genes was reported by Christensen et al. and LaBianca et al. in FHM cases [19, 20].

4 Conclusions

We found lack of association between studied Tatar cases and known mutations in CACNA1A, ATP1A2, and SCN1A genes previously found in the FHM. We believe that FHM in studied Tatar cases is associated with a novel mutations, possibly, in genes not included in this study. We postulate that sequencing a complete genome of the Tatar FHM cases will help to identify new mutations, thus improving our understanding of the disease genetic predisposition. Molecular and genetic studies of FHM revealed fundamental role of the genetic mechanisms explaining many of clinical features of the migraine. Collected data will facilitate the identification of the novel genetics biomarkers of the FHM, which will improve diagnosis of the disease.